Dermatomyositis With Necrotizing Vasculitis, Pulmonary Arterial Hypertension, and Extensive Calcinosis Following Delayed Diagnosis.

Dermatomyositis is a rare autoimmune inflammatory disease with a highly heterogeneous clinical presentation and potential for multisystem involvement. Early diagnosis may be challenging, particularly in patients presenting with amyopathic disease and limited initial laboratory abnormalities. We report the case of a 45-year-old woman initially diagnosed with amyopathic dermatomyositis based on characteristic cutaneous manifestations in the absence of objective muscle involvement on laboratory testing and electromyography. After being lost to follow-up for four years, she presented with progressive proximal muscle weakness, extensive ulcerative calcinosis, Raynaud phenomenon, and exertional dyspnea. Extended myositis serology revealed anti-Mi-2 and anti-signal recognition particle (SRP) antibodies. Muscle biopsy demonstrated perifascicular atrophy, necrotizing vasculitis, and foreign-body granulomatous inflammation associated with dystrophic calcinosis. Right heart catheterization confirmed pre-capillary pulmonary arterial hypertension in the absence of interstitial lung disease. The patient was treated with intravenous cyclophosphamide, pulmonary vasodilator therapy, colchicine, and tapering corticosteroids, resulting in clinical and functional improvement. This case highlights the potential progression of initially amyopathic dermatomyositis to severe systemic disease, the limitations of isolated serological assessment, and the importance of long-term follow-up. It also illustrates several uncommon manifestations of adult dermatomyositis, including extensive calcinosis, pulmonary arterial hypertension, and histologically proven necrotizing vasculitis, supporting the concept of dermatomyositis as a systemic vasculopathic disorder.