Use clinical features suggest a lipid metabolic myopathy, carnitine deficiency disorder, and additional clinical features are seen in carnitine deficiency to frame the working diagnosis and next step; use it only when it changes interpretation or management. Make carnitine deficiency disorder the checkpoint that determines whether you escalate testing, narrow the differential, or change treatment.

Carnitine deficiency can worsen during pregnancy and mimic proximal myopathies; Variable CK and liver enzyme abnormalities are common in carnitine deficiency; Prolonged fasting and extended exercise point toward a lipid metabolic myopathy; Short stature and multisystem involvement should raise suspicion for mitochondrial disease; MRI lesions that ignore vascular territories are a classic mitochondrial clue