High prevalence of myositis in a southeastern United States pediatric systemic lupus erythematosus cohort.

Inflammatory myositis is reported in 4-16% of adult systemic lupus erythematosus (SLE) patients. The aim of this study was to determine the prevalence of myositis in a cohort of pediatric SLE patients in the southeastern United States. A retrospective chart review was performed of 55 SLE patients evaluated by Pediatric Rheumatologists in Alabama since January 1, 2008. Patients were defined as having myositis if they satisfied one of the following categories: 1) Proximal muscle weakness on exam with lower extremity muscle edema on MRI; 2) Proximal muscle weakness with elevation in CK, AST, aldolase, or LDH muscle enzymes; or 3) Patient reported weakness or muscle pain and an elevated CK. Inflammatory myositis was present as a feature of SLE in 31% (n = 17) with a 95% confidence interval of 19-45%, statistically different from the reported rates of 4-16% (p < 0.0001). Myositis was positively associated with the presence of anti-ribonucleoprotein antibodies (p = 0.009). Negative associations with myositis were the presence of anti-double stranded DNA antibodies (p = 0.02) and hematologic disorders (p = 0.02). Thus, in the state of Alabama, pediatric SLE myositis is present at a statistically higher rate than previously published values of adult SLE myositis, possibly reflecting geographic (genetic or environmental) and/or age-of-onset related influence(s).