A Late-Onset Presentation of Miyoshi Myopathy: A Case Report

Miyoshi myopathy is a muscular dystrophy disease characterized by muscle weakness and atrophy generally in distal muscle groups, such as in the legs and arms. Miyoshi myopathy is thought to occur due to genetic mutations in the DYSF gene, which codes for the dysferlin protein, which is critical for muscle cell membrane integrity and muscle fiber adhesiveness. The first symptoms begin in early adulthood and include weakness and atrophy in the calves, gait abnormalities, pain and discomfort in affected muscles, and difficulty jumping or walking on tiptoes. Patients generally are diagnosed by a combination of physical exam findings, genetic testing, muscle biopsy, and elevated creatinine kinase (CK) levels. Management of the disease progression includes physical therapy to strengthen the muscles, nutritional support, occupational therapy, and assisted device education. While not life-threatening, Miyoshi myopathy outlook is generally considered moderate to poor due to significant muscle weakness and eventual loss of mobility usually in 10-20 years after onset. We present a unique case of a 66-year-old male patient complaining of pain in his bilateral calves after having had a series of back surgeries 10 years prior. A diagnosis of Miyoshi myopathy, a rare occurrence in this age group, was made based on CK levels. In this report, we will discuss the pathophysiology, disease progression, and management of Miyoshi myopathy.