Spontaneous Intramuscular Hemorrhage in Anti-melanoma Differentiation-associated Gene 5 Antibody-positive Dermatomyositis.

Anti-melanoma differentiation-associated gene 5 (MDA5) antibody-positive dermatomyositis (DM) is characterized by mild or absent muscle involvement and unique skin lesions such as cutaneous ulceration and palmar papules, commonly associated with rapidly progressive interstitial lung disease (RP-ILD), causing fatal outcomes. Spontaneous intramuscular hemorrhage (SIH) is an extremely rare but severe complication that remains under-recognized in DM. Here, we report a case of multiple SIH in a 72-year-old Japanese woman with anti-MDA5 antibody-positive DM and RP-ILD. The patient initially presented with fever, fatigue, and abnormal liver function, leading to a provisional diagnosis of autoimmune hepatitis. Following a 3-week moderate-dose prednisolone treatment, bilateral thigh hematomas suddenly developed without trauma or anticoagulant therapy. Laboratory findings revealed elevated creatine kinase and ferritin levels, reduced factor XIII (F13) activity, and anemia. Computed tomography (CT) imaging showed hematomas in multiple muscles and ILD. Although high-dose prednisolone administration gradually ameliorated the intramuscular hemorrhage, skin manifestations indicative of DM and dyspnea on exertion emerged after tapering prednisolone. Exacerbation of ILD was observed on CT imaging. Comprehensive analysis detected anti-MDA5 and anti-Ro52 antibodies without anti-F13 autoantibody, eventually leading to the diagnosis of anti-MDA5 antibody-positive DM with SIH and RP-ILD. Despite aggressive immunosuppressants, she died of RP-ILD-related respiratory failure. This case highlights the importance of considering DM as a differential diagnosis and investigating cutaneous manifestations indicative of DM in cases where the SIH etiology is unclear. Evaluation of myositis-specific and myositis-associated autoantibodies is crucial to ensure adequate diagnosis when SIH associated with DM is highly suspected.