A Patient With Late-onset Limb-girdle Muscular Dystrophy Type 2B Mimicking Dermatomyositis: A Case Report and Review

Limb-Girdle Muscular Dystrophy 2B (LGMD2B) presents with proximal and/or distal muscle weakness and markedly high creatine kinase level. It is caused by the loss of dysferlin due to mutations in the DYSF gene. Due to its similar clinical features as inflammatory myopathy, it is often difficult to distinguish between the two. We present a case of a 48-year-old male who developed progressive proximal muscle weakness, papulosquamous lesions on the knuckles, elevated levels of muscle enzymes, and electromyogram abnormalities. Based on the clinical presentation, the initial impression was dermatomyositis, yet it was refractory to immunosuppressive therapy. Subsequently, dysferlin immunostaining and genetic analysis led to the final diagnosis of LGMD2B. This case shows that LGMD2B can present with extramuscular symptoms mimicking inflammatory myopathy in later stages of life. Dysferlin immunostaining and/or genetic analysis of the DYSF gene are essential for its diagnosis.