Clinical features of lupus myositis versus idiopathic myositis: a review of 30 cases.

Myositis is a rare but well-recognized complication of systemic lupus erythematosus (SLE). It is reputed to be milder than primary myositis in terms of morbidity and treatment response. This study compares clinical and laboratory features of idiopathic inflammatory myositis in patients with and without evidence of SLE overlap. We performed a case note review of 30 patients with probable or definite polymyositis/dermatomyositis of whom 11 also had definite or probable SLE. Lupus patients were slightly younger at diagnosis than those with primary disease, and more likely to be female. At presentation, quadriceps strength (expressed as a percentage of expected) was significantly reduced in both the lupus (48.9%; 95% CI 29.0-70.4%) and primary (52.0%; 95% CI 43.6-59.4%) myositis groups, and serum creatine phosphokinase (expressed as a multiple of the upper limit of normal) was significantly elevated (11.2; 95% CI 5.3-29.1 vs 10.7; 95% CI 6.1-17.6). During a mean (S.D.) follow-up period of 7.4 (4.1) yr, both groups tended to follow either a relapsing and remitting, or a chronic persistent course, and when last seen quadriceps muscle strength remained significantly depressed. One of the lupus patients and two of the primary myositis patients died due to direct complications of the disease, and one further death was attributable to a complication of therapy. Our results suggest that lupus myositis is often as severe as primary disease and should be treated with equal vigour.