Focal segmental glomerulosclerosis in a patient with hypereosinophilic syndrome

Background: Renal complication in hypereosinophilic syndrome (HES) is rare, with literature scarcely reporting association of this syndrome with glomerular involvement. While the direct effect of eosinophilic infiltration in tissues has been linked to histological damage of the HES, other mechanisms may account for renal involvement too. Case Presentation: We present a case of a 17-year-old male patient, with progressive edema, contact reactive erythematous skin lesions, acute kidney injury, nephrotic syndrome and progressive eosinophilia. His bone marrow biopsy revealed moderate hyperplasia with severe eosinophilia and atypical lymphocytes. His renal biopsy revealed glomeruli, enlarged in volume with mesangial expansion and hypercellularity and segmental thickening of capillary loops. Likewise, some glomeruli showed peripheral hyalinosis with synechiae to Bowman’s capsule. Tubules showed cloudy swelling, mild tubular atrophy and hyaline cylinders. Interstitial area showed infiltrated lymphomononuclear cells, focal with no evidence of eosinophils. Blood vessels were unaltered. Immunofluorescence identified glomeruli with granular mesangial IgM deposition. After corticosteroid treatment, eosinophilia and creatinine values regress to normal range. Conclusions: While our case may suggest the coexistence of two unrelated diseases, further studies are required to assess the pathophysiology of glomerular involvement in HES. Given the possibility that mechanisms other than the direct effect of eosinophils are involved in certain patients