A patient presents with hypotonia, hypoketotic hypoglycemia, and episodes of myoglobinuria with muscle weakness. Which condition fits this presentation?

• A. CPT II deficiency
• B. Pompe disease
• C. Mitochondrial myopathy
• D. Carnitine deficiency

Answer: (D)

The key idea here is a fatty acid oxidation disorder that causes energy shortfalls in muscle and liver during fasting or stress. Carnitine is the shuttle that delivers long-chain fatty acids into mitochondria for beta-oxidation. When carnitine is deficient, this transport is impaired, so fat oxidation drops, ketone production falls, and you get hypoketotic hypoglycemia. Muscles then lack sufficient fat-derived energy, leading to weakness and, with muscle breakdown, myoglobinuria (rhabdomyolysis). Hypotonia reflects the overall energy deficit in muscles. So this combination—hypotonia, hypoketotic hypoglycemia, and episodes of myoglobinuria with muscle weakness—fits carnitine deficiency best.

Pompe disease centers on glycogen storage issues with proximal weakness and often cardiomyopathy, not the hypoketotic hypoglycemia or myoglobinuria pattern. Mitochondrial myopathy can cause exercise intolerance and lactic acidosis with characteristic muscle pathology, but not the specific hypoketotic hypoglycemia. CPT II deficiency is another fatty acid oxidation disorder that can cause myoglobinuria, especially with exercise, but the systemic transport defect of carnitine deficiency is the classic explanation for this particular triad.