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Anti-PM-Scl Overlap — SCE Rheumatology MCQ

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ModerateConnective Tissue DiseaseAnti-PM-Scl OverlapSCE Rheumatology

A 50-year-old woman has Raynaud's phenomenon, sclerodactyly and symmetrical proximal muscle weakness. Her creatine kinase is 2400 IU/L, antinuclear antibody staining is nucleolar, and anti-PM/Scl antibodies are confirmed. Which clinical phenotype is most strongly associated with this antibody?

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Correct answer: C — Systemic sclerosis–myositis overlap with calcinosis and interstitial lung disease that often has a relatively favourable functional course

Anti-PM/Scl is a myositis-associated antibody that characteristically identifies systemic sclerosis–myositis overlap, often termed scleromyositis. Associated features include inflammatory proximal myopathy, calcinosis, inflammatory arthritis, dermatomyositis-type skin changes and interstitial lung disease. ILD is common rather than rare, but EUSTAR data indicate a comparatively favourable functional pulmonary outcome; it should not be described as invariably mild or benign. Antisynthetase syndrome is defined by antibodies to aminoacyl-tRNA synthetases such as Jo-1. Inclusion body myositis causes a characteristic asymmetric finger-flexor and quadriceps pattern and responds poorly to immunosuppression. Immune-mediated necrotising myopathy is more strongly associated with anti-SRP or anti-HMGCR. Isolated systemic sclerosis does not account for the elevated CK and proximal weakness.

Reference: Lazzaroni MG et al. The clinical phenotype of systemic sclerosis patients with anti-PM/Scl antibodies: results from the EUSTAR cohort. Rheumatology. 2021;60:5028–5041. https://pubmed.ncbi.nlm.nih.gov/33580257/