Overview
Definition
An autosomal recessive glycogen storage disease (Type V) caused by skeletal muscle glycogen phosphorylase deficiency, causing exercise intolerance.
Epidemiology
Prevalence ~1 in 100,000.
Etiology & Risk Factors
- PYGM gene mutations
- Inability to break down glycogen in skeletal muscle during anaerobic exercise
Clinical Symptoms
- Exercise-induced muscle pain and cramping
- Fatigue
- Myoglobinuria (dark-colored urine after exercise)
- Second-wind phenomenon (improvement in exercise tolerance after brief rest)
Clinical Approach
Diagnosis
- Non-ischemic forearm exercise test showing lack of lactate rise
- Genetic testing of PYGM gene
Management
- Moderate aerobic training
- Ingestion of sucrose/simple carbohydrates before exercise
- Avoiding intense isometric exercise
Complications
- Acute Rhabdomyolysis
- Acute Kidney Injury from myoglobinuria
- Compartment syndrome