Approach to diagnosis of oxidative metabolism disorders.

Mitochondrial oxidation of a variety of substrates produces the bulk of energy requirements for most cell types. Impairment of oxidative metabolism may result in a broad spectrum of clinical signs and symptoms. A disorder of oxidative metabolism should be suspected when an unexplained association of signs and symptoms occurs, particularly when it is progressive, involving organs with no common embryologic origin. Encephalopathy and myopathy are a particularly suspect combination. Numerous specific disorders affect oxidative metabolism. Lactate elevation frequently occurs and additional laboratory abnormalities often assist in focusing investigation. Diagnostic specificity may require, in addition to the blood and urine studies, tissue sampling, cerebral imaging, in vivo studies of tissue energetics, or molecular genetic analysis.