Symptoms of disorders of lipid metabolism
How do disorders of lipid metabolism present clinically?
In patients with disorders of lipid metabolism, symptoms such as muscle pain, stiffness/tightness, or myoglobinuria are usually induced by events such as prolonged low-intensity exercise (hiking, soccer), prolonged fasting, infection, general anesthesia, exposure to cold, and low carbohydrate, high-fat diets. The heart, skeletal muscle, and liver depend on fatty acid oxidation for energy. Metabolic blocks in fatty acid oxidation result in accumulation of abnormal amounts of fatty acid in those tissues, leading to cardiomyopathy, weakness, and fatty liver. An increasing number of neurologic diseases have been associated with defects in fatty acid metabolism. Many of them cause abnormalities in the CNS.
Few disorders of lipid metabolism present as isolated exercise intolerance without other organ involvement. Primary muscle carnitine deficiency and CPT II deficiency can present with predominantly muscle disease. In contrast to patients with glycogen metabolic defects, patients with these lipid metabolism defects often do not experience muscle cramps. They do not have the second wind phenomenon. CK levels at rest and the EMG are usually normal or only show mild abnormalities.
