Objective: To determine the clinical impact of muscle involvement in a large systemic sclerosis (SSc) cohort.
Method: Using the Canadian Scleroderma Research Group (CSRG) database, SSc patients with either elevated creatine kinase (CK) or a prior history of myositis/myopathy were identified. Regression and Kaplan-Meier analyses were performed to determine characteristics associated with muscle involvement in SSc and survival outcome.
Results: In 1145 patients with SSc, 5.6% had an elevated CK. This subset was more likely to be male (24.5% in elevated CK vs. 12.6% in normal CK, p < 0.013), younger (52 vs. 56 years, p < 0.045), have diffuse cutaneous SSc (dcSSc; 40.4% vs. 37.9%, p < 0.002), tendon friction rubs (30.0% vs. 13.4%, p < 0.001), and forced vital capacity (FVC) < 70% (23.9% vs. 13.1%, p < 0.039), be ribonucleoprotein (RNP) antibody positive (12.0% vs. 5.0%, p < 0.032), topoisomerase1 (topo1)-antibody positive (26.0% vs. 14.4%, p < 0.026), have a higher modified Rodnan skin score (MRSS; 16.14 vs. 9.81, p < 0.001), and a higher Health Assessment Questionnaire (HAQ) score (0.98 vs. 0.79, p < 0.011). Survival was reduced for patients with elevated CK (p < 0.025). Nearly 10% of patients in the CSRG cohort had a prior history of myositis/myopathy. This subset also had findings similar to those with elevated CK and increased mortality (p < 0.003).
Conclusions: Muscle involvement in SSc has a poor prognosis impacting survival, especially in men with early dcSSc with topo1 and RNP autoantibodies and interstitial lung disease (ILD).