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, n = 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. Muscle Nerve 39: 586–590, 2009