Microscopic polyangiitis. A systemic vasculitis with a positive P-ANCA.

A young girl presented with a purpuric rash on lower limbs, fever, eosinophilia, peripheral neuropathy and progressive renal insufficiency. She developed vesicles, purpuric macules and papules on the head, several nodules on the palmar sides of hands and fingers, splinter haemorrhages, and a disfiguring, facial oedema. A renal biopsy specimen disclosed a focal and segmental necrotizing glomerulonephritis with crescents. Peripheral ANCA with antimyeloperoxidase specificity [P-ANCA (MPO)] was positive and cytoplasmic ANCA with PR3 specificity was negative. Treatment with prednisone and cyclophosphamide was started with a good clinical response, stabilization of renal insufficiency and disappearance of P-ANCA (MPO). Our case fulfils the diagnostic criteria for microscopic polyangiitis (microscopic polyarteritis, MPA), namely a segmental necrotizing and crescentic glomerulonephritis associated with extrarenal vasculitis involving small-sized vessels, without granulomas or asthma. This is a rare disease, which has a poor prognosis in the absence of aggressive therapy, and is infrequently reported in dermatological journals.