Hypereosinophilic Syndrome with Skin Lesions and Secondary Membranous Nephropathy

Introduction: Hypereosinophilic syndrome (HES) is a rare disorder characterized by persistently high absolute eosinophil count (AEC) (>1500 cells/μL), which leads to organ damage due to cell infiltration. Clinical presentations encompass diverse organ systems, including skin, heart, lungs, and gastrointestinal tract. While uncommon, HES can have renal involvement. Approximately 25-30% of cases of membranous nephropathy (MN) are secondary in nature, with HES being a possible but infrequent cause. Case Description: A 63-year-old undomiciled male, with a history of alcohol use disorder and evolving hypereosinophilia for over a year, presented for generalized pruritus and a widespread scaly erythematous rash with excoriations. Extensive infectious workup was unremarkable. A bone marrow biopsy ruled out neoplasm, and a skin biopsy showed no evidence of scabies. Despite empiric treatment for scabies and strongyloides, the patient's AEC continued to rise, reaching 13,000 cells/microL. Laboratory evaluation revealed rising serum creatinine to 5.0 mg/dL and a urine protein-to-creatinine ratio of 3.3. These findings prompted a kidney biopsy, which demonstrated severe interstitial fibrosis, tubular damage, patchy lymphoplasmacytic interstitial infiltrates, and rare eosinophils. Electron microscopy showed mesangial, subepithelial, and intramembranous immune-type deposits. Immunofluorescence studies revealed IgG and C3 deposits along the glomerular basement membrane, with additional mesangial IgG, IgM, and C3 deposits. Findings were consistent with a diagnosis of secondary MN. The patient initially showed improvement in kidney function with methylprednisolone followed by a tapering regimen of prednisone. However, during the steroid tapering phase, the patient's renal impairment progressed, ultimately necessitating hemodialysis initiation. Discussion: HES is a heterogeneous disorder with diverse clinical presentations. Renal involvement, as exemplified by this case, is uncommon but poses significant morbidity with delayed identification and treatment. While the patient initially responded to steroid therapy, kidney disease progression underscores the complexities of managing HES-related renal complications. A review of the literature identified limited case reports of MN associated with HES, highlighting the rarity of this presentation.