Fasting as a provocative test in neuromuscular diseases

Area of Science:

• Biochemistry
• Exercise Physiology
• Neuromuscular Disorders

Background:

• Muscle substrate utilization is crucial for energy production during exercise.
• Defects in this pathway can lead to exercise intolerance and muscle dysfunction.
• Fasting can unmask metabolic abnormalities not apparent under fed conditions.

Purpose of the Study:

• To evaluate the utility of a 38-hour fast as a provocative test for diagnosing muscle substrate utilization defects.
• To differentiate between various types of myopathies based on their metabolic response to fasting and exercise.

Main Methods:

• A 38-hour fasting protocol was administered to patients suspected of muscle substrate defects and healthy controls.
• Exercise capacity and respiratory exchange ratio were measured before and after fasting.
• Blood samples were analyzed for key metabolites including creatine kinase (CK), free fatty acids (FFA), ketone bodies, carnitine, glucose, and alanine.

Main Results:

• Patients with myophosphorylase deficiency showed increased exercise capacity and reduced CK levels post-fast.
• Patients with lipid myopathies (carnitine deficiency, carnitine palmityl transferase deficiency) exhibited decreased exercise capacity and increased reliance on carbohydrates.
• Fasting exacerbated carnitine abnormalities in a patient with carnitine deficiency.
• Several patients with undefined defects displayed distinct metabolic profiles compared to controls.

Conclusions:

• A 38-hour fast serves as an effective provocative test for identifying defects in muscle substrate utilization.
• The test can help distinguish between different myopathies and may aid in discovering novel genetic disorders affecting muscle metabolism.
• Metabolic profiling during fasting provides valuable insights into muscle energy pathways.