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

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.

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.

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.

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.