[Two cases of classical polyarteritis nodosa associated with a low titre of MPO-ANCA]

We studied two autopsy cases, each with a low titre of myeloperoxidase anti-neutrophil cytoplasmic antibody (MPO-ANCA) associated with systemic vasculitis. It was difficult to distinguish these cases from classic polyarteritis nodosa. The patients had suffered from continuous fever, malaise, and weight loss: however, their renal insufficiency was clinically mild over the course of their disease. The patients were diagnosed initially as having MPO-ANCA-associated vasculitis and were treated with prednisolone. Their clinical status improved, but unfortunately, they died of an infectious disease. Autopsies revealed systemic vasculitis in small arteries with no signs of necrotizing and crescentic glomerulonephritis. Our pathologist subsequently diagnosed both cases as classic polyarteritis nodosa. Systemic vasculitis associated with MPO-ANCA is usually considered to be a microscopic polyarteritis. However, classic polyarteritis nodosa should always be considered as a possibility for those patients with mild renal insufficiency and a low titre of MPO-ANCA.