Mesoamerican Nephropathy: Pathological Characteristics
Mesoamerican Nephropathy: Pathological Characteristics
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.
Data from the questionnaire are listed in Table 1 and 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.
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 .
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).
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.
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.
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.
(Enlarge Image)
Figure 1.
Light 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).
(Enlarge Image)
Figure 2.
Light 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.
(Enlarge Image)
Figure 3.
Transmission 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 andC 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).
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 and 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.
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).
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.
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.
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.
(Enlarge Image)
Figure 1.
Light 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).
(Enlarge Image)
Figure 2.
Light 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.
(Enlarge Image)
Figure 3.
Transmission 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 andC 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).