Background/Purpose

Patients with systemic sclerosis (SSc) and muscle involvement (myopathy/myositis) have more severe disease and worse outcomes. We sought to determine the prevalence of muscle disease in our cohort of SSc patients and to compare these patients to those without muscle disease.

Methods

We conducted a retrospective medical record review of patients with SSc according to 2013 ACR classification criteria, evaluated at Stanford from 2006-2013. We collected demographics, clinical features if ever present, Manual Muscle Test 8 (MMT-8), laboratory data (available autoantibody results and muscle enzymes: CPK, aldolase, LDH, AST and ALT). Muscle involvement was defined by the presence of any of the following criteria: elevation in muscle enzyme(s), physician reported history of myopathy/myositis, and if performed, electromyelogram, MRI, and/or muscle biopsy results consistent with myopathy/myositis. Comparisons between SSc patients with and without muscle disease were made with Student’s t-test for continuous variables and chi-square or Fisher’s exact test for categorical variables.

Results

The study included 273 patients (mean age 57.3 years, 88.7% female, 54.6% Caucasian, 37.4% diffuse, and 62.6% limited). Muscle disease was present in 80 patients (29.3%). The most common findings of muscle disease at presentation were elevated muscle enzymes (42.5%) and proximal muscle weakness (42.5%). The first manifestation of muscle disease occurred at a mean time of 7.1±11.1 years after the first non-Raynaud symptom of SSc.  As expected, patients with muscle disease were more likely to have diffuse disease, arthralgias, myalgias, muscle weakness, dysphonia, mechanic hands, greater maximum modified Rodnan skin score, lower MMT-8 scores, and positive PM-1 antibody (p<0.03).  They had less vascular manifestations such as Raynaud's phenomenon (73.8% vs 87.1%; p=0.008) and telangiectasias (7.5% vs 21.8%; p=0.005) and were less likely to be centromere positive (21.3% vs 36.3%, p=0.02). Cardiac disease was more common in patients with muscle disease (13.8% vs 5.7%, p=0.03).  

Conclusion

30% of our SSc cohort had muscle disease, which was associated with a higher likelihood of cardiac disease. Obtaining baseline and routine monitoring of muscle enzymes and performing strength exams at every visit may help to identify patients with SSc with muscle involvement who are also at risk for cardiac disease. The current development of a multi-center SSc cohort of patients with muscle disease led by SCTC and EUSTAR will help elucidate the pathophysiology and better define the subtypes of muscle disease in SSc.

Table 1. Baseline characteristics of 80 patients with muscle disease

*Information available in 46 patients

**Any combination of MRI, EMG, muscle biopsy and muscle enzymes