Anticardiolipin antibodies in polymyalgia rheumatica-giant cell arteritis: association with severe vascular complications. PURPOSE: We studied a group of patients with polymyalgia rheumatica (PMR) with or without biopsy-proven giant cell arteritis (GCA) in order to determine the prevalence of anticardiolipin antibodies (aCL) in these disorders and their association with vascular complications. PATIENTS AND METHODS: The study consisted of 50 patients, 30 with PMR alone and 20 with associated GCA. Determinations of IgG and IgM aCL by enzyme-linked immunosorbent assay were done in the patients and in 50 age- and sex-matched healthy control subjects. We also measured von Willebrand factor (vWF) antigen, C-reactive protein, and erythrocyte sedimentation rate. RESULTS: Twenty-four (48%) of the 50 patients had aCL. Eleven were positive for IgG and five for IgM, whereas eight were positive for both. In the group of patients with PMR alone, only eight (26.6%) had aCL, while 16 of 20 patients (80%) with GCA had these antibodies (p less than 0.01). In the control group, 10 of 50 patients (20%) had positive aCL, a finding that was statistically significantly different only when compared with the finding in patients with GCA (p less than 0.01). Both isotypes of aCL were seen mainly in patients with GCA, and five of these patients had severe vascular complications. Levels of vWF antigen were significantly higher in patients with GCA as compared with patients with PMR alone; however, the highest titers did not correlate with vascular complications. Erythrocyte sedimentation rate and C-reactive protein were increased but comparable in both groups. CONCLUSION: This study demonstrates that aCL are prevalent in patients with GCA. These antibodies might imply severe vascular damage and could play an important role in the pathogenesis of the vasculopathy observed in this disease. 