Atypical presentation of anti-small ubiquitin-like modifier 1 and melanoma differentiation-associated gene 5 antibody positive dermatomyositis presenting with significant inflammatory myopathy on biopsy and normal creatine kinase levels: A case report

Abstract

Idiopathic inflammatory myopathies are characterized by chronic inflammation of skeletal muscle. The main subtypes of idiopathic inflammatory myopathies include dermatomyositis, polymyositis, and necrotizing autoimmune myopathies. Dermatomyositis is characterized by symmetrical proximal muscle weakness, distinctive skin lesions, and systemic manifestations. Dermatomyositis commonly presents with elevated creatinine kinase levels. However, we report a case of a 19-year-old female presenting with dermatomyositis positive for anti-small ubiquitin-like modifier 1 and melanoma differentiation-associated gene 5 antibodies presenting with classic signs and symptoms like progressive proximal muscle weakness, dysphagia, hyperpigmented rash, and Gottron’s papules but had severe inflammatory myopathy on muscle biopsy and normal creatinine kinase levels. This case emphasizes an atypical presentation of dermatomyositis where she did not have amyopathic dermatomyositis despite having a positive anti-melanoma differentiation-associated gene 5 antibody and normal creatinine kinase. This underscores the importance of history and physical examination despite contradictory laboratory results.