McArdle disease

McArdle disease, also known as Glycogen Storage Disease Type V (GSD V), is an autosomal recessive metabolic disorder characterized by a deficiency of muscle phosphorylase. This enzyme defect prevents the breakdown of glycogen into glucose in muscle cells, leading to exercise intolerance, muscle pain, cramps, and sometimes rhabdomyolysis and myoglobinuria. Symptoms typically manifest in childhood or adolescence.

Use this code for patients diagnosed with McArdle disease based on clinical presentation, muscle biopsy showing absence of phosphorylase activity, or genetic testing confirming pathogenic variants in the PYGM gene. This code is appropriate for both initial diagnosis and ongoing management of the condition.

• Confirm documentation specifies McArdle disease (GSD V) and not other glycogen storage diseases.
• Code any associated complications, such as rhabdomyolysis (R82.1) or acute kidney injury (N17.9), separately.
• Review genetic testing results or muscle biopsy reports to support the diagnosis.