Polyarteritis presenting with thrombocytosis and palliated by plasma exchange.

A 66-year-old patient with polyarteritis nodosa presented with thrombocytosis and was found to have circulating immune complexes. Treatment by plasma exchange produced symptomatic improvement and lowered both the platelet count and the level of immune complexes. While plasma exchange is a useful technique in investigating the pathogenesis of the disease, predisolone is a more convenient way of treating it.