Diagnostic measures for patients with systemic sclerosis-associated myopathy

Objective. To evaluate the clinico-serological profile and to assess diagnostic parameters of myopathy in patients with systemic sclerosis (SSc)-associated myopathy. Methods. We explored the profiles of SSc-myopathy patients and matched non-myopathy SSc patients as well as different diagnostic measures for muscle affection. Additionally, the muscle performance of SSc-myopathy patients, assessed by the Manual Muscle Test for 8 muscle groups (MMT-8) and the Functional Index-2 (FI-2), was compared with that of patients with primary myositis. Results. In SSc-myopathy patients, the following features occurred significantly more often even after Bonferroni correction for multiple comparisons: immunosuppressive treatment (56.0% vs. 24.1%; p=0.0003), elevated levels of creatine kinase (CK) (48.3% vs. 5.3%, p<0.0001), anti-PM-Set antibodies (30.4% vs. 4%, p=0.00048), and absence of RNA Polymerase III antibodies (7.3% vs. 28.3%, p<0.0001). The MMT-8 showed a mild muscle weak-ness in SSc-myopathy as well as in primary myositis patients with similar age and sex. Muscle endurance tested by the FI-2 was generally compromised in both cohorts, yet the distribution pattern of affected muscle groups differed between the two cohorts. Conclusion. We confirmed previously described clinic-serological characteristics of SSc-myopathy patients. Our study suggests that autoantibody profile and CK levels may be helpful in establishing the diagnosis of SSc-myopathy. Whole-body MRI might be more accurate to capture the disease extent than MRI of selected muscle groups. Functional muscle tests validated for primary myositis did not perform well for the assessment of muscle function in patients with SSc-myopathy. Both, potential confounders such as skin, joint, and cardiovascular involvement as well as lack of sensitivity might have negatively affected the test performance in this population.