Muscle carnitine levels in neuromuscular disease.

The production of energy in muscle from long-chain fatty acid oxidation is dependent upon the presence of carnitine. An abnormally low level of muscle carnitine, as seen in patients with the carnitine deficiency syndrome, results in marked muscle weakness. Muscle from 83 consecutive patients undergoing diagnostic muscle biopsy was assayed for carnitine. Carnitine levels (mean +/- SEM, expressed as nmoles carnitine per mg noncollagen protein) in muscle from patients with Duchenne dystrophy (8.1 +/- 1.7) and possible Becker dystrophy (10.6 +/- 3.0) were significantly (P less than 0.001) different from histologically normal muscle (24.0 +/- 1.4). Carnitine levels in patients with limb-girdle dystrophy (16.1 +/- 3.1) and polymyositis/dermatomyositis (16.6 +/- 3.2) were also low, although not as low as in Duchenne dystrophy. Carnitine levels from patients with denervation atrophy (22.1 +/- 3.6), nonspecific fiber atrophy (21.3 +/- 1.3), and a group of miscellaneous neuromuscular diseases (20.4 +/- 1.4) were not significantly different from histologically normal muscle. The low values of carnitine seen in Duchenne dystrophy and a group of possible Becker dystrophy patients may be a nonspecific effect, related to severe muscle damage.