Background/Purpose: Muscle involvement in systemic sclerosis (SSc) has been shown to be heterogeneous. Histopathological pattern seems to be associated with prognosis, but studies evaluating the correlations between muscle involvement subtypes, clinical presentation and outcomes are scarce. The aim of this study was to evaluate the prognostic value of histopathological muscular type in SSc.

Methods: We conducted a retrospective multicenter study involving scleroderma patients who underwent muscle biopsy. Patients’ clinical data were collected and a centralized histopathological assessment was carried out according to the European Neuromuscular Centre (ENMC) recommendations. Patients with no further evaluation after muscular biopsy were excluded. Muscular involvement was classified as fibrosing myopathy (FM, according to Paik, Arthritis Care Research 2017), overlap myositis (OM, according to the Troyanov classification), or immune-mediated necrotizing myopathy (IMNM, according to the ENMC).

Results: Fifty-five scleroderma patients (41 women, 34 diffuse SSc) were included. Mean age at muscle biopsy was 48.6 years (± 14.6). ANA were positive in 53 patients (96.4%) (anti-topoisomerase 1 : 20, anti-PmScl : 6). Forty-six patients (83.6%) had muscular symptoms, 59.6% had elevated CK (742±1031 UI/L). Other SSc manifestations included interstitial lung disease (ILD) (74.5%), pulmonary arterial hypertension (PAH) (13%), cardiac involvement (40%), and renal crisis (12.7%). During follow-up (76.5±59 months), an immunosuppressive or immunomodulating treatment was introduced in 48 patients. Improvement in muscular symptoms or CK was observed in 69.2% of patients. Sixteen patients died, 75.6% of patients were alive 5 years after muscular biopsy.

FM was fond in 28 patients (51%), OM in 13 patients (23.6%), and IMNM in 14 patients (25.4%). Compared to the OM group, patients in the FM group were more often positive for anti-topoisomerase 1 antibodies (53.6% vs 7.7%, p< 0.05) but less frequently positive for anti-PmScl antibodies (3.6% vs 30.8%, p< 0.05). CK level was higher in the IMNM group (1378±1250 UI/L) than in the FM group (448±510, p< 0.05) and in the OM group (713±1385, p< 0.05). Prevalence of ILD, PAH, renal crisis and cardiac involvement was not significantly different between the three groups. Patients in the FM group more often had a history of immunosuppressive treatment before the muscle biopsy, but were less frequently treated thereafter. Muscular outcomes and 5-year survival did not significantly differ between the three groups.

Conclusion: This study found three different patterns of muscle involvement among 55 scleroderma patients. FM was associated with anti-topoisomerase 1 antibodies, OM with anti-PmScl antibodies, whereas IMNM was associated with a higher level of CK. We did not find any significant difference in 5-year mortality or muscular outcome according to histological pattern, while patients with OM or IMNM pattern were more aggressively treated.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/histopathological-patterns-of-muscle-involvement-and-clinical-correlations-in-a-retrospective-cohort-of-scleroderma-patients/