MEASUREMENT OF PLATELET-DERIVED MICROPARTICLE LEVELS USING AN ENZYME-LINKED IMMUNOSORBENT ASSAY IN POLYMYOSITIS AND DERMATOMYOSITIS PATIENTS

Platelet-derived microparticle (PDMP) levels were measured using an enzyme-linked immunosorbent assay (ELISA) to elucidate the role of platelet activation in patients with polymyositis or dermatomyositis (PM/DM). PDMP levels in active PM/DM patients (median 13.3 U/ml, interquartile range 9.9-20.7 U/ml = 16) and those in patients undergoing treatment (12.1 U/ml, 7.4-16.7 U/ml, n = 12) were significantly higher than in controls (6.5 U/ml 5.0-8.4 =U/ml, n = 26, vs. active, P = 0.0001; vs. treatment, P = 0.004). In a paired sampling study, PDMP decreased significantly after glucocorticoid treatment (P = 0.04). PDMP in the active PM/DM patients correlated significantly with serum C-reactive protein levels (r(s) = 0.67, P 0.01). These results suggest that platelets may play an important role in the inflammatory process, and that PDMP level could be a useful marker of inflammatory activity in PM/DM patients.