Metabolic myopathies.

PURPOSE OF REVIEW The metabolic myopathies result from inborn errors of metabolism affecting intracellular energy production due to defects in glycogen, lipid, adenine nucleotides, and mitochondrial metabolism. This article provides an overview of the most common metabolic myopathies. RECENT FINDINGS Our knowledge of metabolic myopathies has expanded rapidly in recent years, providing us with major advances in the detection of genetic and biochemical defects. New and improved diagnostic tools are now available for some of these disorders, and targeted therapies for specific biochemical deficits have been developed (ie, enzyme replacement therapy for acid maltase deficiency). SUMMARY The diagnostic approach for patients with suspected metabolic myopathy should start with the recognition of a static or dynamic pattern (fixed versus exercise-induced weakness). Individual presentations vary according to age of onset and the severity of each particular biochemical dysfunction. Additional clinical clues include the presence of multisystem disease, family history, and laboratory characteristics. Appropriate investigations, timely treatment, and genetic counseling are discussed for the most common conditions.