What is the management plan for McArdle Disease (Glycogen Storage Disease Type V)?

Management of McArdle Disease (Glycogen Storage Disease Type V)

The management of McArdle Disease should focus on dietary modifications with higher protein intake, carbohydrate supplementation before exercise, and appropriate physical activity to improve exercise tolerance and prevent complications such as rhabdomyolysis. 1, 2

Dietary Management

• A high-protein diet (25-30% of total calories) with moderate complex carbohydrates (35-50% of total calories) is recommended for patients with McArdle Disease, particularly for those with muscle involvement (GSD IIIa) 1
• Avoid simple sugars as they cause sudden rises and falls in blood glucose; instead, focus on complex carbohydrates 1
• Pre-exercise carbohydrate consumption, particularly oral sucrose, has shown improvement in exercise performance 3, 4
• Small, frequent meals are recommended to avoid fasting, which can precipitate hypoglycemia 1
• A bedtime snack is important to prevent overnight hypoglycemia 1

Exercise Management

• Regular, moderate-intensity exercise is the only treatment option that has proven beneficial for McArdle patients 4
• Patients should be educated about the "second wind" phenomenon (improvement in exercise tolerance after initial symptoms) 5
• Avoid vigorous or high-intensity exercise, which can trigger rhabdomyolysis 2, 6
• Low-intensity physical activity should be encouraged as it attenuates clinical severity of the disease 4, 5
• Exercise should be preceded by adequate carbohydrate intake to provide alternative fuel source 3, 4

Monitoring and Prevention of Complications

• Regular monitoring of creatine kinase (CK) levels is essential, with severe elevations (>10× ULN) requiring immediate medical attention 7
• Monitor for signs of rhabdomyolysis (severe muscle pain, dark urine) which may lead to acute renal failure 6
• Patients should be educated to recognize early warning signs of a potential crisis (excessive fatigue, muscle pain, tachycardia) 5
• Liver function tests should be monitored as transaminase elevations are common 1
• Assess for potential cardiomyopathy, which can occur in some glycogen storage diseases 1

Pharmacological Interventions

• Limited evidence exists for effective pharmacological treatments 3
• Low-dose creatine supplementation (60 mg/kg/day) may provide minimal subjective benefit in some patients 3
• Vitamin B6 and creatine supplementation may be considered in some cases, though evidence of significant benefit is limited 2, 3
• High-dose creatine (150 mg/kg/day) should be avoided as it may worsen myalgia symptoms 3
• Several medications have shown no benefit and should be avoided: D-ribose, glucagon, verapamil, dantrolene sodium, and branched chain amino acids 3

Long-term Management

• Develop a personalized continuum of care focusing on five key steps: diagnosis, understanding, acceptance, learning, and exercise 5
• Patient education is crucial for self-management and prevention of complications 5
• Regular follow-up with a multidisciplinary team including a metabolic specialist, dietitian, and physical therapist 1, 5
• Monitor for potential development of hepatic complications in long-term follow-up 1
• Genetic counseling should be offered to patients and families due to the autosomal recessive inheritance pattern 2, 4

Acute Management of Crises

• For acute rhabdomyolysis, aggressive hydration is essential to prevent renal failure 6
• In severe cases with acute renal failure, hemodialysis may be necessary 6
• Monitor for and treat electrolyte abnormalities, particularly hyperkalemia 6
• Avoid medications that may exacerbate muscle damage during acute episodes 7, 6
• After resolution of acute episodes, gradual reintroduction of physical activity under supervision is recommended 5