Postpartum-onset anti-PM/Scl-positive dermatomyositis-systemic sclerosis overlap syndrome with reversible...

Polymyositis-scleroderma autoantibody (Anti-PM/Scl) associated connective tissue disease is a recognized overlap syndrome classically characterized by features of polymyositis- systemic sclerosis overlap. However, presentation with a dermatomyositis (DM) phenotype accompanied with interstitial lung disease (ILD) is less commonly reported. Pregnancy and the postpartum period are recognized immunological triggers for overlap syndromes, potentially leading to autoimmune disease. Postpartum-onset inflammatory myopathy with overlap features and significant pulmonary involvement poses substantial diagnostic challenges due to its heterogeneous clinical presentation and evolving serologic profiles.

We present a case of a 25-year-old Palestinian woman presenting with progressive proximal muscle weakness, characteristic dermatomyositis cutaneous manifestations, notable unintentional weight loss, and systemic symptoms 4 months postpartum. Laboratory tests showed markedly elevated creatine kinase and positive antinuclear antibodies, positive anti-PM/Scl antibodies and positive anti-dsDNA antibodies, while anti-U1-RNP antibodies were negative. Imaging demonstrated hepatomegaly and splenomegaly, and pulmonary function testing showed interstitial lung disease (ILD). Muscle biopsy confirmed inflammatory myopathy without typical perifascicular atrophy. The patient showed incomplete clinical response to treatment with corticosteroids and mycophenolate mofetil; however, transitioning to rituximab resulted in substantial clinical, pulmonary, and functional improvement.

This case illustrates a diagnostically challenging presentation of postpartum-onset Anti-PM/Scl-Positive dermatomyositis-systemic sclerosis overlap syndrome complicated by ILD and multisystem involvement. It underscores the diagnostic challenges associated with overlap syndrome and connective tissue disease phenotypes, and supports the potential effectiveness of rituximab in refractory overlap myositis and reversing inflammatory ILD.