Concurrent anti-PM-Scl antibody-associated systemic sclerosis and inclusion body myositis - report of two cases and review of the literature

Objectives: To describe two cases of anti-PM-Scl antibody-associated systemic sclerosis with evidence of inclusion body myositis on muscle biopsy. Methods: Two female patients with anti-PM-Scl antibody-associated systemic sclerosis developed progressive proximal myopathy. Both patients had profound muscle weakness that was refractory to treatment with glucocorticoids with or without other oral immunosuppressive agents. Quadriceps muscle biopsy in both cases indicated inclusion body myositis (IBM). Monthly intravenous immunoglobulin (IVIG) infusions were added to the treatment regimen. Results: One patient's myopathy appears to have temporarily stabilized with IVIG infusions (2 g/Kg) every four weeks, though severe residual muscle weakness has persisted. The other patient's myopathy continues to progress slowly, despite being on 4-weekly IVIG infusions, along with weekly oral methotrexate and 6-monthly rituximab infusions. In this report, we compare these two patients with two similar cases that were previously reported and hypothesize a possible pathomechanism of this association. Conclusion: This extremely rare association of IBM and anti-PM-Scl antibody-associated scleromyositis sheds new light on the possible pathogenesis of IBM. It strengthens the hypothesis that autoimmune muscle disease can potentially trigger myodegeneration. Whether early intervention with aggressive immunosuppressive (C) 2020 Elsevier Inc. All rights reserved.