Myopathic carnitine deficiency is attributed to impairment in the active transportation of carnitine from the plasma into muscle cells. Hence, carnitine level is reduced in muscles and is normal or slightly decreased in plasma and liver.
Clinically, carnitine deficiency manifests during childhood or early adult life as progressive proximal muscle weakness, exertional myalgias, or, rarely, myoglobinuria
Pathologically, the muscle shows an increased number of lipid droplets, especially in type I muscle fibers. Electron microscopy often confirms the abnormal lipid accumulation with minimal or no increase of mitochondria