Fibrosing myopathy in systemic sclerosis: Treatment response and clinical outcomes in a distinct subset

To characterize the clinical features, treatment response, and mortality of patients with systemic sclerosis (SSc) associated fibrosing myopathy.

In this retrospective study, we identified patients enrolled in the Johns Hopkins Scleroderma Center Research Registry with histopathological evidence of fibrosing myopathy. Data were collected regarding SSc features, treatment exposures, and outcomes. Muscle involvement was characterized using muscle enzyme levels, muscle magnetic resonance imaging (MRI) findings, electromyography (EMG) data, and histopathologic features.

16 patients were included in the analysis. 14/16 patients (87.5%) received treatment specifically for muscle disease. Response based on muscle strength testing was evaluated at 6-12 months after treatment initiation. 9/16 patients (56.3%) had significant improvement, 4/16 (25%) showed no significant improvement, and 3/16 (18.8%) had inadequate follow-up. The most commonly used treatments were intravenous immunoglobulin, mycophenolate, and rituximab. After a mean follow-up time of 5.5 ± 4.7 years, 8/16 patients (50%) were deceased, with a cardiopulmonary cause of death in 4/8 (50%) of these patients. The baseline median CK value was 97 U/L (interquartile range 46-300 U/L). Myopathic changes were identified in 14/15 patients (93.3%) who had an EMG performed, while muscle edema was identified in 11/12 patients (91.7%) who underwent an MRI. A notable histopathological finding was myofiber atrophy in the perifascicular region in 9/16 patients (56.3%).

SSc-associated fibrosing myopathy is a distinct entity associated with a high mortality rate in our cohort of patients. Early recognition and initiation of treatment is important due to the potential for improvement in muscle strength.