Evaluation of a screening algorithm to detect systemic sclerosis-related myopathy

Abstract Objectives Prevalence of muscle involvement in systemic sclerosis (SSc) ranges from 6% to 96%. If inflammatory myopathy (IM) is present, early diagnosis enables timely treatment; however, there is no standardized approach to detection. We evaluated a screening algorithm for SSc-related muscle involvement. Methods Consecutive SSc patients in the Australian Scleroderma Cohort Study (ASCS) were assessed annually for clinical features of myopathy proximal weakness and elevated creatine kinase (CK) during routine care, with further investigations performed according to physician judgement. In a subset of patients from South Australia (SA), if weakness and/or elevated CK was present, further assessment with myositis immunoblot and/or muscle MRI (proposed screening algorithm) was applied; positive findings prompted muscle biopsy. Results Among 1443 patients, 260/1407 (18.5%) had weakness and 203/1282 (15.8%) an elevated CK at least once during routine care (median follow-up 5.19 years). 26/1253 (2.1%) had biopsy-proven myopathy (1.4% IM). In SA patients, 117/425 (27.5%) had weakness, 80/421 (19%) elevated CK and 42/423 (9.9%) underwent muscle biopsy based on a positive screen weakness and/or elevated CK (n = 48), myositis-specific/myositis-associated autoantibodies (n = 10) or MRI abnormalities (n = 8). All 42 biopsies were abnormal: IM in 28/42 (66.7%) and non-specific myopathic changes in 14/42 (33.3%), indicating 28/423 (6.6%) SA patients had biopsy-proven IM compared with 18/1253 (1.4%) of the ASCS cohort. IM prompted use of immunomodulatory therapy, with improved muscle power in all cases. Conclusion Biopsy-proven muscle involvement was identified in 9.9% of screened SSc patients, and detection of IM increased by ∼4.5-fold compared with routine care, enabling timely treatment and avoiding unnecessary, potentially harmful immunosuppression in non-inflammatory myopathy.