Advertisement
American Journal of Kidney Diseases

Clinical and Pathological Characterization of Mesoamerican Nephropathy: A New Kidney Disease in Central America

      Background

      An endemic of chronic kidney disease (CKD) of unknown cause among rural inhabitants in Central America has been identified. Young and otherwise healthy men working in plantations are frequently affected. The name Mesoamerican nephropathy (MeN) has been suggested. Clinically, MeN presents with low-grade proteinuria and progressive kidney failure. The renal pathology of this disease has not yet been described.

      Study Design

      Case series.

      Setting & Participants

      8 male patients with CKD of unknown cause and clinically suspected MeN were recruited from a nephrology unit in El Salvador. All recruited patients had been working on plantations. Kidney biopsies, blood, and urine samples were collected.

      Outcomes & Measurements

      Renal morphology examined with light microscopy, immunofluorescence, and electron microscopy; clinical and biochemical characteristics.

      Results

      A similar pattern was seen in all 8 biopsy specimens, with extensive glomerulosclerosis (29%-78%) and signs of chronic glomerular ischemia in combination with tubular atrophy and interstitial fibrosis, but only mild vascular lesions. Electron microscopy indicates podocytic injury. Biochemical workup showed reduced estimated glomerular filtration rate (27-79 mL/min/1.73 m2 with the CKD Epidemiology Collaboration [CKD-EPI] creatinine equation), low-grade albuminuria, and increased levels of tubular injury biomarkers. Hypokalemia was found in 6 of 8 patients.

      Limitations

      Small number of patients from one country.

      Conclusions

      This study is the first report of the biochemical and morphologic findings in patients with MeN. Our findings indicate that MeN constitutes a previously unrecognized kidney disease with damage to both glomerular and tubulointerstitial compartments.

      Index Words

      Rural inhabitants in Central America have an endemic form of chronic kidney disease (CKD) of unknown cause and with as yet insufficiently described clinical and morphologic characteristics.
      • Brooks D.R.
      • Ramirez-Rubio O.
      • Amador J.J.
      CKD in Central America: a hot issue.
      • Ramirez-Rubio O.
      • McClean M.D.
      • Amador J.J.
      • Brooks D.R.
      An epidemic of chronic kidney disease in Central America: an overview.
      The nephropathy was reported to affect primarily young male workers engaged in sugarcane cultivation, but later the disease also was reported in other types of farming. According to local physicians, the affected individuals present with various degrees of CKD but usually are normotensive and have no hematuria, and proteinuria is absent or of non–nephrotic range. At a workshop in Costa Rica in 2012, the disease was named Mesoamerican nephropathy (MeN). Among local health professionals and inhabitants, awareness of the problems involving CKD and subsequent morbidity and mortality in certain regions of Nicaragua, Costa Rica, and El Salvador has been emerging for several years.
      • Cuadra S.N.
      • Jakobsson K.
      • Hogstedt C.
      • Wesseling C.
      Chronic Kidney Disease: Assessment of Current Knowledge and Feasibility for Regional Research Collaboration in Central America.
      Health statistics from the World Health Organization show that El Salvador has the highest mortality rate from kidney disease in the world, especially among male inhabitants.
      World Health Organization (WHO)
      Global burden of disease. Death estimates for 2008 by cause for WHO Member States.
      Four extensive cross-sectional examinations of populations in Central America have used measurements of serum creatinine to confirm the existence of an increased prevalence of CKD in certain rural populations.
      • Torres C.
      • Aragon A.
      • Gonzalez M.
      • et al.
      Decreased kidney function of unknown cause in Nicaragua: a community-based survey.
      • O'Donnell J.K.
      • Tobey M.
      • Weiner D.E.
      • et al.
      Prevalence of and risk factors for chronic kidney disease in rural Nicaragua.
      • Peraza S.
      • Wesseling C.
      • Aragon A.
      • et al.
      Decreased kidney function among agricultural workers in El Salvador.
      • Sanoff S.L.
      • Callejas L.
      • Alonso C.D.
      • et al.
      Positive association of renal insufficiency with agriculture employment and unregulated alcohol consumption in Nicaragua.
      Three of these studies were conducted in Nicaragua, and one, in El Salvador. These studies show a pattern of more males than females being affected,
      • Torres C.
      • Aragon A.
      • Gonzalez M.
      • et al.
      Decreased kidney function of unknown cause in Nicaragua: a community-based survey.
      • O'Donnell J.K.
      • Tobey M.
      • Weiner D.E.
      • et al.
      Prevalence of and risk factors for chronic kidney disease in rural Nicaragua.
      • Peraza S.
      • Wesseling C.
      • Aragon A.
      • et al.
      Decreased kidney function among agricultural workers in El Salvador.
      • Sanoff S.L.
      • Callejas L.
      • Alonso C.D.
      • et al.
      Positive association of renal insufficiency with agriculture employment and unregulated alcohol consumption in Nicaragua.
      villages in which agricultural work (particularly plantation work at low altitude) is the predominant source of employment having a higher prevalence of CKD than service-oriented villages,
      • Torres C.
      • Aragon A.
      • Gonzalez M.
      • et al.
      Decreased kidney function of unknown cause in Nicaragua: a community-based survey.
      • Peraza S.
      • Wesseling C.
      • Aragon A.
      • et al.
      Decreased kidney function among agricultural workers in El Salvador.
      • Sanoff S.L.
      • Callejas L.
      • Alonso C.D.
      • et al.
      Positive association of renal insufficiency with agriculture employment and unregulated alcohol consumption in Nicaragua.
      and proteinuria among affected individuals usually being low.
      • Torres C.
      • Aragon A.
      • Gonzalez M.
      • et al.
      Decreased kidney function of unknown cause in Nicaragua: a community-based survey.
      • O'Donnell J.K.
      • Tobey M.
      • Weiner D.E.
      • et al.
      Prevalence of and risk factors for chronic kidney disease in rural Nicaragua.
      • Peraza S.
      • Wesseling C.
      • Aragon A.
      • et al.
      Decreased kidney function among agricultural workers in El Salvador.
      In the most recent study performed in El Salvador by Peraza et al,
      • Peraza S.
      • Wesseling C.
      • Aragon A.
      • et al.
      Decreased kidney function among agricultural workers in El Salvador.
      664 inhabitants aged 20-60 years in 5 communities were studied; 2 were coastal communities with sugarcane production and 3 communities were located at higher altitude, with sugarcane, coffee, and service-oriented economies. The prevalence of decreased estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2 in men was 18% in the coastal communities with sugarcane production compared to 1% in the communities at higher altitude. Nicaragua has similar areas with low prevalence of CKD.
      • Laux T.S.
      • Bert P.J.
      • Barreto Ruiz G.M.
      • et al.
      Nicaragua revisited: evidence of lower prevalence of chronic kidney disease in a high-altitude, coffee-growing village.
      Many of the affected slowly develop terminal kidney failure. There is a lack of renal replacement therapy facilities with dialysis or kidney transplantation in Nicaragua and El Salvador, and thus many of those affected eventually will die of uremia. According to a recent overview, the death toll from CKD is likely to have reached at least 20,000 in this region.
      • Ramirez-Rubio O.
      • McClean M.D.
      • Amador J.J.
      • Brooks D.R.
      An epidemic of chronic kidney disease in Central America: an overview.
      Considerable efforts have been made to elucidate the cause, or causes, of this endemically occurring CKD. At an early stage, suspicion was raised that the CKD was brought about by occupational exposure to pesticides that frequently are used during sugarcane and cotton production. A research group from Boston (the Boston University investigation of CKD in Western Nicaragua) has carried out a series of studies in Nicaragua in collaboration with a local team of researchers. To date, little evidence has come forth supporting the contention that exposure to agrochemicals, pesticides, heavy metals, or locally occurring infections are causative.
      • McClean M.
      • Amador J.
      • Laws R.
      • et al.
      Biological sampling report: investigating biomarkers of kidney injury and chronic kidney disease among workers in Western Nicaragua.
      Instead, it has been hypothesized that repeated heat stress with excessive sweating and volume depletion during heavy manual work may be a causative factor, perhaps in combination with the use of nonsteroidal anti-inflammatory drugs (NSAIDs), which are easily available over the counter and frequently used.
      • Brooks D.
      • McClean M.
      Summary report: Boston University investigation of chronic kidney disease in Western Nicaragua, 2009-2012.
      The significance of heat stress during long days of hard manual work and possible repeated episodes of fluid depletion is supported by male predominance, a high prevalence in farming villages at a low altitude close to the Pacific coast (where the climate is hottest and most humid), and the occurrence of MeN irrespective of the type of crop produced. In further support of an association between long-term and repeated heat stress, a strong statistical association has been found between the relative risk for elevated creatinine level and years of work on coastal sugarcane or cotton plantations.
      • Peraza S.
      • Wesseling C.
      • Aragon A.
      • et al.
      Decreased kidney function among agricultural workers in El Salvador.
      With the low degree of proteinuria involved, MeN being caused by a tubulointerstitial type of nephritis rather than a glomerular disease has been suggested.
      • Torres C.
      • Aragon A.
      • Gonzalez M.
      • et al.
      Decreased kidney function of unknown cause in Nicaragua: a community-based survey.
      • O'Donnell J.K.
      • Tobey M.
      • Weiner D.E.
      • et al.
      Prevalence of and risk factors for chronic kidney disease in rural Nicaragua.
      • Peraza S.
      • Wesseling C.
      • Aragon A.
      • et al.
      Decreased kidney function among agricultural workers in El Salvador.
      However, only relatively few kidney biopsies have been done in patients from the area, and to our knowledge, no report of the morphology of MeN has been published to date. Thus, the real nature of MeN is unknown.
      In this report, we present clinical and renal morphology features from 8 men who have undergone kidney biopsy and, on a clinical basis, are considered as having MeN. To our knowledge, this report constitutes the first detailed clinical and morphologic description of this kidney disease.

      Methods

      Ethical Statement

      Approval was obtained from the Ethical Committee in Stockholm, Sweden, and Hospital Nacional Rosales, San Salvador, El Salvador. All participating patients gave their informed consent before the study.

      Patients

      Eight male plantation workers with CKD of unknown cause and clinical suspicion of MeN were recruited at the Department of Renal Medicine, Hospital Nacional Rosales, San Salvador, El Salvador. Kidney biopsies, blood and urine samples were collected. The inclusion criteria were CKD of unknown cause, age 20-60 years, and plasma creatinine levels of 1.36-2.49 mg/dL (120-220 μmol/L) or eGFR of 30-60 mL/min/1.73 m2 by the CKD-EPI (CKD Epidemiology Collaboration) creatinine equation. Exclusion criteria were diabetes mellitus (fasting blood glucose >126 mg/dL [>7.0 mmol/L]), uncontrolled hypertension (blood pressure >140/90 mm Hg or treatment with >1 hypertension medicine), or nephrotic-range proteinuria (24-hour protein excretion >3.5 g).

      Procedure

      Overview

      Participants presented fasting on the day of the biopsy. Blood and urine samples were collected before the biopsy procedure was conducted, and blood pressure was tested. No intravenous fluid was given before the collection of blood samples. All patients answered a questionnaire about how long they had been working at plantations; their current use of hypertension medicines, painkillers (NSAIDs and paracetamol), and herbal medicines; daily fluid intake; and smoking habits. The patients stayed at the hospital for observation for 24 hours after the biopsy.

      Kidney Biopsies

      The kidney biopsy procedure was performed at Hospital Nacional Rosales with an ultrasound-guided percutaneous technique using a spring-loaded biopsy needle (DANA/Biocore II MG, 14 gauge; Histo). Preparation of the kidney biopsy specimens was done according to standard procedure and the biopsy specimens were examined with light microscopy, immunofluorescence, and electron microscopy (EM). See Item S1, available as online supplementary material, for more detailed description of the preparation of the biopsies.
      Histologic evaluation of masked samples was performed by 2 experienced renal pathologists (A.W. and M.S.). Tubular atrophy, interstitial fibrosis, and interstitial inflammation were semiquantified as follows: mild, affecting 6%-25% of the cortical area; moderate, 26%-50% of the cortical area; and severe, >50%.
      Thickness of the glomerular basement membrane (GBM) was calculated by measuring the thickness in 5 areas in 5 randomly selected capillaries. The degree of foot-process effacement was semiquantified in the same capillaries by calculating the numbers of slits per length of the GBM.

      Blood Samples

      Two weeks prior to the kidney biopsy, blood samples were collected from the patients for measurements of red and white blood cells and screening for hepatitis B and C virus and HIV (human immunodeficiency virus). These measurements were performed at the Hospital Nacional Rosales laboratory.
      Blood samples obtained on the morning of the kidney biopsy were analyzed for the following constituents at Karolinska University Hospital laboratory according to standard protocols: creatinine (assay standardized to isotope-dilution mass spectrometry), serum urea nitrogen, sodium, potassium, calcium, albumin, uric acid, alanine aminotransferase, phosphate, antineutrophil cytoplasmic antibody and antinuclear antibody screening, complement levels, and anti-GBM antibodies. Specific biochemical markers for renal damage, such as cystatin C (assay standardized to IFCC [Internation Federation of Clinical Chemistry and Laboratory Medicine] standard) and serum β2-microglobulin, also were measured. eGFR was calculated using the CKD-EPI creatinine equation
      • Levey A.S.
      • Stevens L.A.
      • Schmid C.H.
      • et al.
      A new equation to estimate glomerular filtration rate.
      and the CKD-EPI cystatin C equation.
      • Inker L.A.
      • Schmid C.H.
      • Tighiouart H.
      • et al.
      Estimating glomerular filtration rate from serum creatinine and cystatin C.

      Urine Samples

      Urine samples were shipped to Karolinska University Hospital laboratory to be analyzed. Urinary albumin, creatinine, and uric acid, as well as biomarkers for proximal tubular injury, urinary N-acetyl-β-d-glucosaminidase (NAG), and urinary α1-microglobulin (also known as protein HC),
      • Waring W.S.
      • Moonie A.
      Earlier recognition of nephrotoxicity using novel biomarkers of acute kidney injury.
      • D'Amico G.
      • Bazzi C.
      Urinary protein and enzyme excretion as markers of tubular damage.
      were measured (see Item S1 for more detailed description). Additional urine samples were collected 2-3 months after the biopsy for dipstick (Combur-Test; Roche) and manual microscopic examination of sediment at Hospital Nacional Rosales.

      Results

      Study Participants

      Eight male patients aged 22-57 years with CKD of unknown cause were included in the study. All participants had been or were currently working at plantations in rural areas of El Salvador. All patients had normal blood pressure, 100-130/60-80 (mean, 112/71) mm Hg, at the time of the biopsy.

      Questionnaire

      Data from the questionnaire are listed in Table 1, Table 2. All patients had been doing agricultural plantation work, mainly sugarcane or corn, bean, and sorghum production. The number of years working at plantations varied from 8-44 (mean, 32) years. All participants reported that they have a physically strenuous occupation. None of the patients had a history of urinary stones, and only one patient (patient 2) had treatment for hypertension. The patients' own estimated daily liquid intake was 2.5-5 (mean, 3.9) L, of which 50%-90% (mean, 80%) was water.
      Table 1Patient Characteristics
      Patient No.Age (y)BMI (kg/m2)Chronic DiseaseElevation of Residence Area (masl)Fluid intake (L/d)Duration of Plantation Work (y)Smoking (y)
      14726
      Results outside of normal range.
      No422.5300
      24729
      Results outside of normal range.
      Hypertension3605396
      32829
      Results outside of normal range.
      No3785206
      4
      Father of patient 5.
      4420No5225350
      52220No5222.580
      65727
      Results outside of normal range.
      Hyperuricemia4144425
      75335
      Results outside of normal range.
      No4763400
      85621No16444140
      Note: Data from medical records and questionnaire.
      Abbreviations: BMI, body mass index; masl, meters above sea level.
      a Results outside of normal range.
      b Father of patient 5.
      Table 2Regular Use of Hypertension Medications, Herbal Medicines, and NSAIDs at the Time of Biopsy
      Patient No.Hypertension MedicineHerbal MedicinesNSAID Use
      Every DayEvery Week
      100NoNo
      2Nifedipine 30 mg 1×/dTea from “Jiote” bark
      Bursera simbaruba.
      NoYes
      3Enalapril 5 mg 2×/d0YesYes
      40Magnus
      Water-soluble powder with fructose, vitamins and minerals (manufacturer: Omnilife).
      NoYes
      50Magnus
      Water-soluble powder with fructose, vitamins and minerals (manufacturer: Omnilife).
      NoNo
      6Enalapril 5 mg 2×/dWater from Coquillo root
      Astrocaryum alatum.
      NoNo
      700YesYes
      80Cat's claw
      Uncaria tomentosa.
      NoYes
      Abbreviation: NSAID, nonsteroidal anti-inflammatory drug.
      a Bursera simbaruba.
      b Water-soluble powder with fructose, vitamins and minerals (manufacturer: Omnilife).
      c Astrocaryum alatum.
      d Uncaria tomentosa.
      Two of the patients were maintained on aspirin, 100 mg daily. One of the patients was treated with allopurinol due to hyperuricemia. Two of the patients (patients 1 and 7) had been treated with ciprofloxacin for urinary tract infection (UTI) for 2 weeks during the past 6 months. Participants' use of hypertension medicines, herbal medicines, and NSAIDs are presented in Table 2.

      Biochemical Workup

      Blood

      Results of relevant plasma and serum measurements are listed in Table 3. Additional analysis demonstrated that all patients had normal glucose, calcium, albumin, antinuclear antibody, antineutrophil cytoplasmic antibody, anti-GBM, and complement levels. Serum β2-microglobulin levels were elevated at 2.5-6.8 (reference value, < 2.0) mg/L, as was expected due to reduced GFR. Alanine aminotransferase levels were normal in all cases, with the exception of patient 7, who had slightly increased levels: 82.6 U/L (1.38 μkat/L).
      Table 3Results of Blood Analyses
      Patient No.Sodium
      Plasma.
      (mEq/L)
      Potassium (mEq/L)Cr
      Plasma.
      (mg/dL)
      SUN (mg/dL)Uric Acid
      Plasma.
      (mg/dL)
      Hb
      Serum.
      (g/dL)
      eGFRcr (mL/min/1.73 m2)eGFRcys (mL/min/1.73 m2)
      11383.4
      Results outside of normal range.
      1.64
      Results outside of normal range.
      27
      Results outside of normal range.
      9.6
      Results outside of normal range.
      12.8
      Results outside of normal range.
      4961
      2129
      Results outside of normal range.
      3.3
      Results outside of normal range.
      2.73
      Results outside of normal range.
      56
      Results outside of normal range.
      7.811.1
      Results outside of normal range.
      2723
      31384.12.22
      Results outside of normal range.
      197.111.2
      Results outside of normal range.
      3934
      41412.8
      Results outside of normal range.
      1.97
      Results outside of normal range.
      137.512.4
      Results outside of normal range.
      4034
      51402.4
      Results outside of normal range.
      1.28
      Results outside of normal range.
      8
      Results outside of normal range.
      7.114.47960
      61404.72.53
      Results outside of normal range.
      30
      Results outside of normal range.
      6.312.1
      Results outside of normal range.
      2725
      71402.9
      Results outside of normal range.
      1.13
      Results outside of normal range.
      119.3
      Results outside of normal range.
      15.07450
      8122
      Results outside of normal range.
      3.0
      Results outside of normal range.
      2.02
      Results outside of normal range.
      24
      Results outside of normal range.
      6.712.2
      Results outside of normal range.
      3634
      Note: Reference values (Laboratory at Karolinska University Hospital): sodium, 1.55-1.64 mg/dL; potassium, 3.6-4.6 mEq/L; Cr, <1.13 mg/dL; SUN, 9-23 mg/dL; uric acid, 3.9-8.1 mg/dL; Hb, 13.4-17.0 g/dL. Conversion factors for units: Cr in mg/dL to μmol/L, ×88.4; SUN in mg/dL to mmol/L, ×0.357; uric acid in mg/dL to μmol/L, ×59.48.
      Abbreviations: Cr, creatinine; eGFRcr, glomerular filtration rate estimated from creatinine; eGFRcys, glomerular filtration rate estimated from cystatin C; Hb, hemoglobin; SUN, serum urea nitrogen.
      a Plasma.
      b Serum.
      c Results outside of normal range.

      Urine

      Results from urine measurements are listed in Table 4. Urinary NAG-creatinine ratio and urinary α1-microglobulin–creatinine ratio were elevated in the majority of patients, indicating tubular injury. Urine dipstick and sediment were analyzed 2-3 months after the biopsy and showed trace protein in patient 8, 1+ protein in patient 7, and 2+ protein in patient 2. None of the urine samples showed microscopic hematuria, glucosuria, or casts.
      Table 4Results of Urine Analyses
      Patient No.ACR (mg/g)NAG:Cr Ratio (nkat/g)A1M:Cr Ratio (mg/g)
      1<2334
      2788
      Results outside of normal range.
      169
      Results outside of normal range.
      92
      Results outside of normal range.
      36110
      Results outside of normal range.
      119
      Results outside of normal range.
      48149
      Results outside of normal range.
      73
      Results outside of normal range.
      5<782
      Results outside of normal range.
      51
      Results outside of normal range.
      6125316
      Results outside of normal range.
      717163
      Results outside of normal range.
      50
      Results outside of normal range.
      8192
      Results outside of normal range.
      140
      Results outside of normal range.
      39
      Results outside of normal range.
      Note: Reference values (Laboratory at Karolinska University Hospital): ACR, <30 mg/g; NAG:Cr ratio, <71 nkat/g; A1M:Cr ratio, <6 mg/g. Conversion factors for units: ACR in mg/g to mg/mmol, ×0.113; NAG:Cr ratio in nkat/g to nkat/mmol, ×0.113; A1M:Cr ratio in mg/g to mg/mmol, ×0.113.
      Abbreviations: A1M, α1-microglobulin; ACR, urine albumin-creatinine ratio; Cr, creatinine; NAG, N-acetyl-β-d-glucosaminidase.
      a Results outside of normal range.

      Kidney Biopsies

      Overview

      All biopsy specimens were evaluated by light microscopy, immunofluorescence, and EM. The light microscopic picture is described in Table 5. Biopsy specimens included 10-27 glomeruli.
      Table 5Light Microscopy Findings
      Pt 1Pt 2Pt 3Pt 4Pt 5Pt 6Pt 7Pt 8
      Total no. of glomeruli1820161018271730
      Globally sclerosed glomeruli50%65%38%40%44%78%29%70%
      Segmentally sclerosed glomeruli0%5%0%0%0%7%0%0%
      Interstitial fibrosis
      Scale, 0-3 D/F.
      1-2 F2-3 F1 F2 F1 F2 F1 F2 F
      Tubular atrophy
      Scale, 0-3.
      12120-120-12
      Tubulitis
      Scale, 0-3.
      01000000
      Interstitial inflammation
      Scale, 0-3.
      12121102
      Glomerular size
      Scale, 0-3.
      23121312
      Mesangial matrix expansion
      Scale, 0-3.
      01000-100-10
      Wrinkled GBM/thickened Bowman capsule
      Scale, 0-1.
      11111110-1
      Intimal thickening
      Scale, 0-3.
      01000001
      Smooth muscle hyperplasia
      Scale, 0-3.
      01-211-21111
      Arteriolar hyalinosis
      Scale, 0-3.
      01000101
      Abbreviations: D, diffuse; F, focal; GBM, glomerular basement membrane; pt, patient.
      a Scale, 0-3 D/F.
      b Scale, 0-3.
      c Scale, 0-1.

      Glomerular Changes

      All biopsy specimens showed varying degrees of global glomerulosclerosis, affecting 29%-78% of included glomeruli (Fig 1A-C). Wrinkling of glomerular capillary basement membranes and/or thickening of Bowman capsules were seen in all but one biopsy specimen (Fig 1D and Fig S1A). In patient 8, these changes were mild. All biopsy specimens showed glomerular enlargement (Fig 2A), and in 2 patients, segmental glomerular sclerotic lesions were observed. In patient 2, segmental sclerosis was of the cellular type (Fig 2B). In patient 6, sclerotic lesions were perihilar (Fig S1B). There was no endocapillary cell proliferation. Discrete mesangial matrix increase was seen in a few patients, but there was no increase in number of mesangial cells. No crystals were seen in polarized light. In all patients, immunoglobulins, complement, fibrinogen, and light chains were undetectable by immunofluorescence.
      Figure thumbnail gr1
      Figure 1Light microscopic changes in kidney biopsy specimens from patients with Mesoamerican nephropathy. All biopsy specimens showed varying extent and distribution of global glomerulosclerosis, both in (A) small scars (arrow; periodic acid–Schiff) and (B, C) more dispersed (B: arrowhead; C: arrowhead; periodic acid–Schiff–methenamine silver and hematoxylin and eosin, respectively). (D) Most biopsy specimens showed signs of chronic ischemia with wrinkling of capillary basement membranes and/or thickening of Bowman capsules (periodic acid–Schiff–methenamine silver). (A) Varying degrees of tubular atrophy were seen in all biopsy specimens (arrow). (C) Chronic mononuclear inflammation was seen in atrophic areas. (B) Arterial smooth muscle hyperplasia was found in some patients (arrow). (C) Arteriolae were mostly normal (arrow), but some showed mild hyalinosis. Bars = 50 μm (D), 200 μm (B, C), 500 μm (A).
      Figure thumbnail gr2
      Figure 2Light microscopy changes in kidney biopsy specimens from patients with Mesoamerican nephropathy. (A) Glomerular enlargement was seen in all biopsy specimens (hematoxylin and eosin). In 2 patients, focal segmental lesions were found in glomeruli; (B) in patient 2, the lesion was of cellular type (periodic acid–Schiff). (C) Mild to moderate tubular atrophy and chronic interstitial inflammation was seen in most patients (Ladewig). (D) Most arteries showed no intimal fibrosis (hematoxylin and eosin). (A) Three of 8 patients displayed mild arteriolar hyalinosis.
      The findings of the electron microscopic evaluation are presented in Table 6. The specimens included one glomerulus, except the specimen from patient 7, in which the material contained 5 glomeruli. In general, the material for EM showed fixation artifacts, most prominently in tubuli. Segmental foot-process effacement was observed in 3 patients. In 6 of 8 patients, the podocyte cytoplasm contained a variable number of vacuoles, most prominently in patient 1 (Fig 3A and Fig S2C). The membranes of most vacuoles were smooth and only a few had ribosomes (Fig 3A). In 3 of 8 patients, fat droplets were found (Fig 3B and Fig S2C). Mesangial areas did not show significant pathology, except in patient 7, in which small amounts of electron-dense deposits were found, indicating immune complexes (Fig S2D). Immunofluorescence also was performed on pronase-treated paraffin-embedded material in this patient, and small amounts of mesangial immunoglobulin G (IgG) deposits could thereby be identified. However, IgA and IgM results were negative. Based on results from these findings, we conclude that the immune complexes probably represent a remnant of a previous episode of glomerulonephritis, such as postinfectious glomerulonephritis, which in itself was not enough to explain the overall morphologic picture.
      Table 6Electron Microscopy Findings
      Patient No.GBM Thickness (nm)Podocyte Foot Processes (slits/μm GBM)Endothelial CellsMesangiumPodocyte Cytoplasm
      1430
      Normal.
      1.7 (1.4-2.0)NormalNormalGreat no. of vacuoles; lipid droplets
      2625
      Thickened.
      0.9 (0.3-1.4)
      Segmental effacement.
      NormalNormalGreat no. of vacuoles
      3470
      Mildly thickened.
      1.6 (1.3-1.9)NormalNormalSlightly increased no. of vacuoles; lipid droplets
      4380
      Normal.
      1.0 (0.4-1.7)
      Segmental effacement.
      NormalNormalModerate increased no. of vacuoles
      5360
      Normal.
      1.3 (1.0-1.9)NormalNormalModerate increased no. of vacuoles
      6390
      Normal.
      1.3 (1.0-1.9)NormalNormalNormal
      7360
      Normal.
      1.3 (1.0-1.6)NormalElectron-dense depositsModerate increased no. of vacuoles; lipid droplets
      8340
      Normal.
      1.2 (0.6-1.4)
      Segmental effacement.
      NormalNormalNormal
      Note: Values for podocyte foot processes are given as mean number of slits per micrometer GBM (range of the 5 different areas of measurements).
      Abbreviation: GBM, glomerular basement membrane.
      a Normal.
      b Thickened.
      c Segmental effacement.
      d Mildly thickened.
      Figure thumbnail gr3
      Figure 3Transmission electron image from biopsy specimen from patient 1 shows (A) numerous empty vacuoles (v) with smooth membranes in the podocyte cytoplasm. In some areas, similar vacuoles covered with ribosomes are found (arrows). (B) In podocytes from patient 7, the cytoplasm contains some vacuoles (arrowheads) and lipid droplets in clusters (arrows). Bars = (A) 500 nm, (B) 5 μm.

      Tubulointerstitial Changes

      In general, tubuli showed extensive fixation artifacts. Long-term changes were seen in all patients, with varying degrees of tubular atrophy and interstitial fibrosis (Figs 1A and 2C and Figs S1C, S1D and S2A). In 4 of 8 patients, the changes were mild, and in the other 4, they were moderate. Varying degrees of chronic inflammation were seen (Fig 2C and Fig S2B). None of the patients showed severe changes. Patient 2 showed mild tubulitis. There were no granulocytes found in the tubular lumina and thus no signs of acute pyelonephritis. No eosinophils were found in 7 patients, but in patient 8, a few eosinophils were found in peritubular capillaries.
      EM showed no lead inclusions in tubular nuclei, but further examination of tubular cells could not be done due to fixation artifacts.

      Vascular Changes

      Arterial changes were mild (Fig 2D). In only 2 biopsy specimens was mild intimal fibrosis observed. In most patients, mild hyperplasia of smooth muscle cells was identified (Fig 1B and Fig S1A). Only 3 biopsy specimens showed mild arteriolar hyalinosis (Fig 2A), whereas no arteriolar changes were found in 5 biopsy specimens (Fig 1C).

      Discussion

      To our knowledge, the present study is the first report correlating clinical data with biochemical and morphologic findings in patients with MeN.
      The 8 patients in this study all have risk factors associated with MeN, such as plantation work and male sex. They display a homogenous clinical appearance with normal blood pressure, no diabetes, and low-grade or absent albuminuria. Most of them showed increased urinary excretion of NAG and/or α1-microglobulin (Table 4). The morphologic evaluations of the kidney biopsy specimens show a similar pattern that does not resemble any other common specific kidney disease. This indicates that MeN, clinically and morphologically, constitutes a new and unique diagnostic entity.
      The morphologic picture was similar in biopsy specimens of all included patients. Chronic tubulointerstitial damage with tubular atrophy and interstitial fibrosis was found in combination with chronic glomerular changes. The most striking and surprising finding was the presence of relatively extensive globular sclerosis, involving 29%-78% of glomeruli analyzed. This morphologic pattern contrasts with the chronic interstitial nephritis described in 2 other types of endemic nephropathies, Chinese herb nephropathy and Balkan nephropathy, characterized by chronic tubulointerstitial changes and preserved glomeruli.
      • Vanherweghem J.L.
      • Depierreux M.
      • Tielemans C.
      • et al.
      Rapidly progressive interstitial renal fibrosis in young women: association with slimming regimen including Chinese herbs.
      • Soderland P.
      • Lovekar S.
      • Weiner D.E.
      • Brooks D.R.
      • Kaufman J.S.
      Chronic kidney disease associated with environmental toxins and exposures.
      • Cosyns J.P.
      • Jadoul M.
      • Squifflet J.P.
      • De Plaen J.F.
      • Ferluga D.
      • van Ypersele de Strihou C.
      Chinese herbs nephropathy: a clue to Balkan endemic nephropathy?.
      The pathogenesis of the glomerular sclerosis in our patient cohort is unclear. In all but one biopsy specimen, glomeruli showed changes typical of chronic ischemia, with wrinkling of glomerular capillaries and/or thickening of Bowman capsule. Chronic glomerular ischemia is a common finding in diseases or conditions with vascular damage, such as hypertensive kidney disease
      • Colvin R.B.
      Diagnostic Pathology.
      or aging.
      • Glassock R.J.
      • Rule A.D.
      The implications of anatomical and functional changes of the aging kidney: with an emphasis on the glomeruli.
      However, all our patients were normotensive and showed only mild changes in the arteries and arterioli, which makes the finding of widespread global sclerosis even more noteworthy. The absence of proteinuria and negative immunofluorescence findings in all but one patient do not support that chronic glomerulonephritis is an underlying cause.
      The glomerular enlargement found in all biopsy specimens could be secondary to the widespread glomerulosclerosis with nephron loss, but other factors such as ischemia or other hemodynamic derangements in the kidney might contribute. Glomerular hypertrophy often is seen in adaptive focal segmental glomerulosclerosis, and the increase in glomerular volume may be one of mechanisms in the development of glomerulosclerosis.
      • D'Agati V.D.
      • Kaskel F.J.
      • Falk R.J.
      Focal segmental glomerulosclerosis.
      • Brenner B.M.
      • Meyer T.W.
      • Hostetter T.H.
      Dietary protein intake and the progressive nature of kidney disease: the role of hemodynamically mediated glomerular injury in the pathogenesis of progressive glomerular sclerosis in aging, renal ablation, and intrinsic renal disease.
      Focal segmental sclerotic lesions were observed in 2 patients, albeit without significant proteinuria, which usually is the typical clinical manifestation of focal segmental glomerulosclerosis. Both the biochemical data and morphologic picture indicate a component of chronic tubulointerstitial damage that was both focal and diffuse. Chronic inflammation also was present, although not more than could be expected in atrophic areas. We did not see acute inflammation, but chronic pyelonephritis is more difficult to exclude because the morphologic picture in chronic pyelonephritis is unspecific, with tubular atrophy and interstitial fibrosis. Two patients in our study had been treated for UTIs within the previous 6 months, but had no history of repeated UTIs. There have been reports of a high incidence of UTI symptoms among sugarcane workers in Nicaragua, but a recent investigation with urine cultures from 50 of these patients showed no bacteriuria.
      • McClean M.
      • Amador J.
      • Laws R.
      • et al.
      Biological sampling report: investigating biomarkers of kidney injury and chronic kidney disease among workers in Western Nicaragua.
      The clinical presentation of our 8 patients show CKD stages 2-4 (eGFR, 27-79 mL/min/1.73 m2) with urinary findings of no or non−nephrotic-range albuminuria, no hematuria, and increased levels of biochemical urinary markers for tubular damage (NAG and α1-microglobulin). These results mainly indicate a tubulointerstitial disease, and the morphologic finding of extensive glomerular sclerosis therefore was surprising. However, this observation provides important information for future studies regarding the pathogenic mechanisms of this disease.
      Interestingly, a morphologic picture similar to that found in our patients has been described in endemic CKD of unknown cause in farmers in Sri Lanka.
      • Chandrajith R.
      • Nanayakkara S.
      • Itai K.
      • et al.
      Chronic kidney diseases of uncertain etiology (CKDue) in Sri Lanka: geographic distribution and environmental implications.
      • Nanayakkara S.
      • Komiya T.
      • Ratnatunga N.
      • et al.
      Tubulointerstitial damage as the major pathological lesion in endemic chronic kidney disease among farmers in North Central Province of Sri Lanka.
      • Athuraliya N.T.
      • Abeysekera T.D.
      • Amerasinghe P.H.
      • et al.
      Uncertain etiologies of proteinuric-chronic kidney disease in rural Sri Lanka.
      In the most recent study by Nanayakkara et al,
      • Nanayakkara S.
      • Komiya T.
      • Ratnatunga N.
      • et al.
      Tubulointerstitial damage as the major pathological lesion in endemic chronic kidney disease among farmers in North Central Province of Sri Lanka.
      64 patients with CKD of unknown cause underwent kidney biopsy and it was concluded that tubulointerstitial damage was the main pathologic lesion. However, they also reported global glomerular sclerosis and ischemic glomerular changes, and the authors concluded that neither of these glomerular changes correlated with clinical parameters such as hypertension. Most likely, hypertension contributed to the glomerulosclerosis found in that study because most of the patients had hypertension (55%) and chronic vascular lesions.
      Environmental toxins have been discussed as a potential cause of the endemic nephropathy in Sri Lanka,
      • Chandrajith R.
      • Nanayakkara S.
      • Itai K.
      • et al.
      Chronic kidney diseases of uncertain etiology (CKDue) in Sri Lanka: geographic distribution and environmental implications.
      • Nanayakkara S.
      • Komiya T.
      • Ratnatunga N.
      • et al.
      Tubulointerstitial damage as the major pathological lesion in endemic chronic kidney disease among farmers in North Central Province of Sri Lanka.
      as well as in MeN. However, there is no evidence of, for example, cadmium or lead toxicity in the patients with MeN.
      • O'Donnell J.K.
      • Tobey M.
      • Weiner D.E.
      • et al.
      Prevalence of and risk factors for chronic kidney disease in rural Nicaragua.
      • McClean M.
      • Amador J.
      • Laws R.
      • et al.
      Biological sampling report: investigating biomarkers of kidney injury and chronic kidney disease among workers in Western Nicaragua.
      Moreover, the morphologic picture of lead toxicity differs from those seen in our patients. In 1974, Cramer et al
      • Cramer K.
      • Goyer R.A.
      • Jagenburg R.
      • Wilson M.H.
      Renal ultrastructure, renal function, and parameters of lead toxicity in workers with different periods of lead exposure.
      studied kidney biopsy specimens from lead-exposed workers. They found ultrastructural tubular changes and interstitial fibrosis, while the glomeruli and blood vessels were spared. In another study of chronic lead nephropathy, chronic tubulointerstitial changes were described in combination with some sclerotic glomeruli, but also marked chronic vascular lesions.
      • Inglis J.A.
      • Henderson D.A.
      • Emmerson B.T.
      The pathology and pathogenesis of chronic lead nephropathy occurring in Queensland.
      Glomerular sclerosis has not been described in cadmium toxicity.
      • Bonnell J.A.
      • Ross J.H.
      • King E.
      Renal lesions in experimental cadmium poisoning.
      • Van Vleet T.R.
      • Schnellmann R.G.
      Toxic nephropathy: environmental chemicals.
      Repeated dehydration due to heavy physical labor in a hot climate has been suggested as one of the causes of MeN.
      • Brooks D.R.
      • Ramirez-Rubio O.
      • Amador J.J.
      CKD in Central America: a hot issue.
      • Ramirez-Rubio O.
      • McClean M.D.
      • Amador J.J.
      • Brooks D.R.
      An epidemic of chronic kidney disease in Central America: an overview.
      • Cuadra S.N.
      • Jakobsson K.
      • Hogstedt C.
      • Wesseling C.
      Chronic Kidney Disease: Assessment of Current Knowledge and Feasibility for Regional Research Collaboration in Central America.
      • O'Donnell J.K.
      • Tobey M.
      • Weiner D.E.
      • et al.
      Prevalence of and risk factors for chronic kidney disease in rural Nicaragua.
      • Peraza S.
      • Wesseling C.
      • Aragon A.
      • et al.
      Decreased kidney function among agricultural workers in El Salvador.
      Severe dehydration is a well-known cause of acute kidney injury, and during the past decade, a number of studies have shown that patients who have had transient acute kidney injury have an increased risk of developing CKD/end-stage renal disease.
      • Coca S.G.
      • Singanamala S.
      • Parikh C.R.
      Chronic kidney disease after acute kidney injury: a systematic review and meta-analysis.
      • Chawla L.S.
      • Kimmel P.L.
      Acute kidney injury and chronic kidney disease: an integrated clinical syndrome.
      • Bedford M.
      • Farmer C.
      • Levin A.
      • Ali T.
      • Stevens P.
      Acute kidney injury and CKD: chicken or egg?.
      • Ishani A.
      • Xue J.L.
      • Himmelfarb J.
      • et al.
      Acute kidney injury increases risk of ESRD among elderly.
      The renal morphology in patients developing CKD after acute kidney injury has not been described, thus making a comparison with the morphology found in this study impossible. However, a recent experimental study by Grgic et al
      • Grgic I.
      • Campanholle G.
      • Bijol V.
      • et al.
      Targeted proximal tubule injury triggers interstitial fibrosis and glomerulosclerosis.
      demonstrated that repeated injury to proximal tubules could result in global glomerular sclerosis. One therefore can speculate whether the glomerular sclerosis seen in our patients is only a phenomenon secondary to tubular damage. Although we cannot exclude that the tubular injury may contribute to the glomerular damage, the relation between the chronic tubulointerstitial and glomerular changes suggests a primary injury to the glomeruli.
      A finding that indicates glomerular injury is the observation of vacuoles and lipid droplets in the podocyte cytoplasm. This finding was not expected considering the low range of proteinuria found in our cohort. The podocytic ultrastructural changes in our material do not resemble those previously observed in lead toxicity.
      • Cramer K.
      • Goyer R.A.
      • Jagenburg R.
      • Wilson M.H.
      Renal ultrastructure, renal function, and parameters of lead toxicity in workers with different periods of lead exposure.
      A majority of our patients had a frequent intake of analgesic drugs, including NSAIDs. Intake of NSAIDs may cause kidney failure due to allergic tubulointerstitial nephritis, characterized by tubulitis and interstitial inflammatory infiltrate containing eosinophils and sometimes granuloma. These changes were not found in the biopsy specimens from our patients. There is no epidemiologic evidence that nonphenacetin analgesics or NSAIDs cause CKD.
      • Kurth T.
      • Glynn R.J.
      • Walker A.M.
      • et al.
      Analgesic use and change in kidney function in apparently healthy men.
      • Curhan G.C.
      • Knight E.L.
      • Rosner B.
      • Hankinson S.E.
      • Stampfer M.J.
      Lifetime nonnarcotic analgesic use and decline in renal function in women.
      • Agodoa L.Y.
      • Francis M.E.
      • Eggers P.W.
      Association of analgesic use with prevalence of albuminuria and reduced GFR in US adults.
      However, NSAIDs inhibit the vasodilative effect of prostaglandins and thereby change renal hemodynamics. Constriction of the afferent arteriole decreases kidney perfusion pressure, which hypothetically may contribute to the chronic glomerular ischemia found in our patients. One can speculate whether these changes might be aggravated further by dehydration and subsequent activation of the renin-angiotensin-aldosterone system because the plantation workers operate in extremely hot areas. The hypokalemia found in 6 of our patients is noteworthy as a possible result of renin-angiotensin-aldosterone system activation and calls for further investigation.
      Taken as a whole, our data indicate both tubulointerstitial and glomerular damage in the kidney. However, this study presents only a small number of patients with clinical MeN from El Salvador and may not be representative for other cases of clinically suspected MeN in Central America. Additional studies of biopsies from other endemic areas are warranted.
      The pathogenic mechanisms causing the changes described in this study are unclear, and further studies are needed. However, our data indicate that steroids probably will not be beneficial for these patients because the inflammatory component is limited. A brief overview of the findings in this study was presented at the First International Research Workshop on MeN held in 2012 in Costa Rica,
      • Wernerson Östman A.
      • Wijkström J.
      • Elinder C.G.
      • Leiva R.
      Morphological examination of renal biopsies to assess and evaluate nephrotoxicity, and in particular Mesoamerican Nephropathy.
      and we believe that our findings have and will generate new and important hypotheses for future studies about the cause of this major health problem in Central America.

      Acknowledgements

      A summary of the findings in this study has been presented at the First International Research Workshop on Mesoamerican Nephropathy in San José, Costa Rica, November 28-30, 2012.
      The authors thank the dedicated staff at the nephrology unit at Hospital Nacional Rosales and Drs Ana Lidia Benitez and Eliseo Guzman for support; Associate Professor Peter Barany for fruitful discussions of the results; the Njur-KBC research department at Karolinska University Hospital for assistance with urine and blood tests; and Anneli Hansson, Ingrid Lindell, Anna-Karin Ramqvist, and Eva Blomén for skillful technical assistance.
      Support: Financial support was provided through the regional agreement on medical training and clinical research (ALF) between Stockholm County Council and Karolinska Institutet and by Rinds Stiftelse. The study sponsors have had no role in study design, collection of data, analysis of data, writing the manuscript, or the decision to submit the manuscript for publication.
      Financial Disclosure: The authors declare that they have no other relevant financial interests.

      Supplementary Material

      • Supplementary Figure S1 (PDF)

        Light microscopy images. Biopsy from patient 2 (A, PASM) show thickening of Bowman's capsule (arrow head) and an artery with smooth muscle hyperplasia (arrow). These findings were frequently seen in this case series. Focal segmental lesions were found in two patients, in patient 6 the lesion was of perihilar type (B arrow head, PAS). Mild to moderate chronic tubulointerstitial changes with tubular atrophy (C arrow, HE) and interstitial fibrosis (D arrow, Ladewig) were observed in all patients.

      References

        • Brooks D.R.
        • Ramirez-Rubio O.
        • Amador J.J.
        CKD in Central America: a hot issue.
        Am J Kidney Dis. 2012; 59: 481-484
        • Ramirez-Rubio O.
        • McClean M.D.
        • Amador J.J.
        • Brooks D.R.
        An epidemic of chronic kidney disease in Central America: an overview.
        J Epidemiol Community Health. 2013; 67: 1-3
        • Cuadra S.N.
        • Jakobsson K.
        • Hogstedt C.
        • Wesseling C.
        Chronic Kidney Disease: Assessment of Current Knowledge and Feasibility for Regional Research Collaboration in Central America.
        in: SALTRA, Heredia, Costa Rica2006 (Work & Health Series No 2)
        • World Health Organization (WHO)
        Global burden of disease. Death estimates for 2008 by cause for WHO Member States.
        (Accessed December 9, 2012)
        • Torres C.
        • Aragon A.
        • Gonzalez M.
        • et al.
        Decreased kidney function of unknown cause in Nicaragua: a community-based survey.
        Am J Kidney Dis. 2010; 55: 485-496
        • O'Donnell J.K.
        • Tobey M.
        • Weiner D.E.
        • et al.
        Prevalence of and risk factors for chronic kidney disease in rural Nicaragua.
        Nephrol Dial Transplant. 2011; 26: 2798-2805
        • Peraza S.
        • Wesseling C.
        • Aragon A.
        • et al.
        Decreased kidney function among agricultural workers in El Salvador.
        Am J Kidney Dis. 2012; 59: 531-540
        • Sanoff S.L.
        • Callejas L.
        • Alonso C.D.
        • et al.
        Positive association of renal insufficiency with agriculture employment and unregulated alcohol consumption in Nicaragua.
        Ren Fail. 2010; 32: 766-777
        • Laux T.S.
        • Bert P.J.
        • Barreto Ruiz G.M.
        • et al.
        Nicaragua revisited: evidence of lower prevalence of chronic kidney disease in a high-altitude, coffee-growing village.
        J Nephrol. 2012; 25: 533-540
        • McClean M.
        • Amador J.
        • Laws R.
        • et al.
        Biological sampling report: investigating biomarkers of kidney injury and chronic kidney disease among workers in Western Nicaragua.
        (April 26, 2012) (Accessed December 9, 2012)
        • Brooks D.
        • McClean M.
        Summary report: Boston University investigation of chronic kidney disease in Western Nicaragua, 2009-2012.
        (August 2012) (Accessed December 9, 2012)
        • Levey A.S.
        • Stevens L.A.
        • Schmid C.H.
        • et al.
        A new equation to estimate glomerular filtration rate.
        Ann Intern Med. 2009; 150: 604-612
        • Inker L.A.
        • Schmid C.H.
        • Tighiouart H.
        • et al.
        Estimating glomerular filtration rate from serum creatinine and cystatin C.
        N Engl J Med. 2012; 367: 20-29
        • Waring W.S.
        • Moonie A.
        Earlier recognition of nephrotoxicity using novel biomarkers of acute kidney injury.
        Clin Toxicol. 2011; 49: 720-728
        • D'Amico G.
        • Bazzi C.
        Urinary protein and enzyme excretion as markers of tubular damage.
        Curr Opin Nephrol Hypertens. 2003; 12: 639-643
        • Vanherweghem J.L.
        • Depierreux M.
        • Tielemans C.
        • et al.
        Rapidly progressive interstitial renal fibrosis in young women: association with slimming regimen including Chinese herbs.
        Lancet. 1993; 341: 387-391
        • Soderland P.
        • Lovekar S.
        • Weiner D.E.
        • Brooks D.R.
        • Kaufman J.S.
        Chronic kidney disease associated with environmental toxins and exposures.
        Adv Chronic Kidney Dis. 2010; 17: 254-264
        • Cosyns J.P.
        • Jadoul M.
        • Squifflet J.P.
        • De Plaen J.F.
        • Ferluga D.
        • van Ypersele de Strihou C.
        Chinese herbs nephropathy: a clue to Balkan endemic nephropathy?.
        Kidney Int. 1994; 45: 1680-1688
        • Colvin R.B.
        Diagnostic Pathology.
        in: Kidney Diseases. 1st ed. Amirsys, Salt Lake City, UT2011
        • Glassock R.J.
        • Rule A.D.
        The implications of anatomical and functional changes of the aging kidney: with an emphasis on the glomeruli.
        Kidney Int. 2012; 82: 270-277
        • D'Agati V.D.
        • Kaskel F.J.
        • Falk R.J.
        Focal segmental glomerulosclerosis.
        N Engl J Med. 2011; 365: 2398-2411
        • Brenner B.M.
        • Meyer T.W.
        • Hostetter T.H.
        Dietary protein intake and the progressive nature of kidney disease: the role of hemodynamically mediated glomerular injury in the pathogenesis of progressive glomerular sclerosis in aging, renal ablation, and intrinsic renal disease.
        N Engl J Med. 1982; 307: 652-659
        • Chandrajith R.
        • Nanayakkara S.
        • Itai K.
        • et al.
        Chronic kidney diseases of uncertain etiology (CKDue) in Sri Lanka: geographic distribution and environmental implications.
        Environ Geochem Health. 2011; 33: 267-278
        • Nanayakkara S.
        • Komiya T.
        • Ratnatunga N.
        • et al.
        Tubulointerstitial damage as the major pathological lesion in endemic chronic kidney disease among farmers in North Central Province of Sri Lanka.
        Environ Health Prev Med. 2012; 17: 213-221
        • Athuraliya N.T.
        • Abeysekera T.D.
        • Amerasinghe P.H.
        • et al.
        Uncertain etiologies of proteinuric-chronic kidney disease in rural Sri Lanka.
        Kidney Int. 2011; 80: 1212-1221
        • Cramer K.
        • Goyer R.A.
        • Jagenburg R.
        • Wilson M.H.
        Renal ultrastructure, renal function, and parameters of lead toxicity in workers with different periods of lead exposure.
        Br J Ind Med. 1974; 31: 113-127
        • Inglis J.A.
        • Henderson D.A.
        • Emmerson B.T.
        The pathology and pathogenesis of chronic lead nephropathy occurring in Queensland.
        J Pathol. 1978; 124: 65-76
        • Bonnell J.A.
        • Ross J.H.
        • King E.
        Renal lesions in experimental cadmium poisoning.
        Br J Ind Med. 1960; 17: 69-80
        • Van Vleet T.R.
        • Schnellmann R.G.
        Toxic nephropathy: environmental chemicals.
        Semin Nephrol. 2003; 23: 500-508
        • Coca S.G.
        • Singanamala S.
        • Parikh C.R.
        Chronic kidney disease after acute kidney injury: a systematic review and meta-analysis.
        Kidney Int. 2012; 81: 442-448
        • Chawla L.S.
        • Kimmel P.L.
        Acute kidney injury and chronic kidney disease: an integrated clinical syndrome.
        Kidney Int. 2012; 82: 516-524
        • Bedford M.
        • Farmer C.
        • Levin A.
        • Ali T.
        • Stevens P.
        Acute kidney injury and CKD: chicken or egg?.
        Am J Kidney Dis. 2012; 59: 485-491
        • Ishani A.
        • Xue J.L.
        • Himmelfarb J.
        • et al.
        Acute kidney injury increases risk of ESRD among elderly.
        J Am Soc Nephrol. 2009; 20: 223-228
        • Grgic I.
        • Campanholle G.
        • Bijol V.
        • et al.
        Targeted proximal tubule injury triggers interstitial fibrosis and glomerulosclerosis.
        Kidney Int. 2012; 82: 172-183
        • Kurth T.
        • Glynn R.J.
        • Walker A.M.
        • et al.
        Analgesic use and change in kidney function in apparently healthy men.
        Am J Kidney Dis. 2003; 42: 234-244
        • Curhan G.C.
        • Knight E.L.
        • Rosner B.
        • Hankinson S.E.
        • Stampfer M.J.
        Lifetime nonnarcotic analgesic use and decline in renal function in women.
        Arch Intern Med. 2004; 164: 1519-1524
        • Agodoa L.Y.
        • Francis M.E.
        • Eggers P.W.
        Association of analgesic use with prevalence of albuminuria and reduced GFR in US adults.
        Am J Kidney Dis. 2008; 51: 573-583
        • Wernerson Östman A.
        • Wijkström J.
        • Elinder C.G.
        • Leiva R.
        Morphological examination of renal biopsies to assess and evaluate nephrotoxicity, and in particular Mesoamerican Nephropathy.
        in: Wesseling C. Crowe J. Hogstedt C. Jakobsson K. Lucas R. Wegman D. Mesoamerican Nephropathy: Report from the First International Research Workshop on MeN. SALTRA/IRET-UNA, Heredia, C.R.2013: 59 (Accessed June 22, 2013)