Diagnostic value of in situ muscle fiber conduction velocity measurements in myopathies.

In situ studies on muscle fiber conduction velocity (MFCV) were performed in 54 patients with histologically and biochemically defined myopathies. MFCV was measured over a 10 cm segment of the rectus femoris muscle by intramuscular stimulation and recording. Muscle disorders included muscular dystrophies, myotonic dystrophy, inflammatory myopathies, metabolic myopathies, endocrine myopathies, and congenital myopathies with structural abnormalities. Ten healthy volunteers served as controls. MFCV was significantly reduced in all patients except those with a defect in glycolysis and those that had recovered from acute myositis. MFCV did not vary with either sex. age or the duration of the disease. This shows that MFCV slowing is an unspecific finding in most myopathies. However, in some patients with normal needle electromyography, MFCV provided additional information in diagnosing muscle disease.