[PS4-1D-3] Genetic Muscle Disease Differentiating From Inflammatory Myositis
Differentiating genetic muscle disease from inflammatory myositis can be challenging because of similar presentation. Making the correct diagnosis can prevent patients with genetic disease from being exposed to the risks of immunosuppressive medications, which benefit those with inflammatory myositis. Examples are presented to highlight important clinical features that assist in the differentiation between the two. Clinical features including age at onset, history, pattern of weakness, serum creatine kinase activity, electromyography findings, and muscle biopsies are reported in five patients initially thought to have an inflammatory myositis in whom the final diagnosis was a genetic muscle disease, including LMNA-related muscular dystrophy in five cases and Thymidine kinase 2-related mtDNA depletion syndrome in one case. We emphasize aspects of the medical history, physical exam, laboratory evaluation, muscle biopsy, and next generation sequencing that can help clinicians distinguish myositis mimics from true autoimmune myositis. The key distinguishing clinical were minimal to no response to immunosuppression. Patients diagnosed with inflammatory myositis should be reevaluated for the possibility of a genetic muscle disease if they fail to respond to immunosuppression treatment, and genetic tests should be performed.