Hairy-cell leukaemia with polyarteritis nodosa.

In four patients a systemic vasculitis similar to polyarteritis nodosa developed within 2 years of the onset of hairy-cell leukaemia. Arteriographic studies in two patients revealed microaneurysms, and biopsy specimens in three patients revealed a vasculitis affecting medium-sized vessels. Blood neutrophilia and neutrophilic vascular infiltrate were absent. One patient had circulating immune complexes. Two patients responded to corticosteroids alone, one required cyclophosphamide as well as steroids, and one improved without chemotherapy. The association of vasculitis with hairy-cell leukaemia may provide insight into the pathogenesis of arteritis.