Introduction:

Antineutrophil cytoplasmic autoantibodies (ANCAs) are crucial in the pathogenesis of ANCA-associated glomerulonephritis. Although highly specific for this disease, these antibodies can appear in healthy individuals or occur in other settings such as malignance, other inflammatory disease, or drugs. Renal biopsy remains essential for diagnosis and as a prognostic tool. Failing to perform a biopsy risks an incomplete evaluation or misdiagnosis.

Clinical case:

A 60-year-old male known to have had previous normal kidney function was admitted with generalized pitting edema, nonpruritic erythematous rash, and decreased urine output. He had been recently started on clozapine for depression. Laboratory tests revealed nephrotic syndrome with massive proteinuria (11g/day), hematuria and elevated serum creatinine that reached a maximum of 4.9 mg/dl. The only positive finding was a high titer of myeloperoxidase (MPO) ANCA antibody (111 UI/ml). Clozapine was discontinued, and he was started on conservative management of the nephrotic syndrome. The rash disappeared within one week. Kidney biopsy showed cellular variant focal segmental glomerulosclerosis (FSGS) with mild acute tubular injury. The patient was treated with oral prednisolone with complete remission. Repeat MPO-ANCA was negative after one month.

Discussion:

We present a challenging case that highlights the importance of kidney biopsy for accurate diagnosis with major impact on treatment and prognosis. This case also underlines the presentation and evolution of FSGS cellular variant, a rare and poorly understood disease. The relationship between skin rash with high MPO titer and the administration of clozapine with clinical remission after its discontinuation favors the hypothesis of drug associated ANCA-vasculitis.

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