Metabolic Myopathies

Metabolic myopathies are genetic disorders that impair intermediary metabolism in skeletal muscles. Impairments in glycolysis or glycogenolysis, fatty acid transport and oxidation, and the mitochondrial respiratory chain represent the majority of known defects. Metabolic myopathies can present in the neonatal period and infancy with hypotonia, hypoglycemia, and encephalopathy; however, most cases are present in childhood or adulthood with exercise intolerance, frequently with rhabdomyolysis and weakness. Clinical examination is often normal between acute events, and evaluation involves exercise testing, blood tests, urinary organic acids, muscle biopsy, MRI spectroscopy, and genetic testing. Interventions with lifestyle and nutritional modification and cofactor treatment can improve the overall outlook.