Factor VIII-von Willebrand factor in giant cell arteritis and polymyalgia rheumatica.

Levels of three factor VIII-von Willebrand factor components (von Willebrand antigen, ristocetin cofactor, and factor VIII coagulant) were higher in specimens of plasma from 27 patients with giant cell arteritis and 18 patients with polymyalgia rheumatica than in specimens from 21 normal control subjects. Values in patients with active giant cell arteritis were higher than those in patients with either inactive giant cell arteritis or active polymyalgia rheumatica. Levels of factor VIII-von Willebrand factor components tended to decline gradually after disease activity had been suppressed by corticosteroid therapy and therefore may be indicators of vascular damage. These levels, however, did not revert to normal rapidly in response to corticosteroid therapy as did the patients' symptoms and the usual laboratory measurements indicative of inflammation; thus, measurements of these components are unlikely to be useful in day-to-day management of these diseases. Electrophoretic analysis suggested that the elevated values are due to increased amounts of normal factor VIII-von Willebrand factor rather than to the presence of an abnormal molecule.