Conduction velocity along muscle fibers in situ in Duchenne muscular dystrophy.
The muscle fibers of the biceps brachii muscle were stimulated distally with low voltage by means of two monopolar needles in 14 boys with Duchenne muscular dystrophy (DD). The electric activity was recorded proximally by means of a SFEMG electrode. The mean conduction velocity of 508 muscle fibers in situ (MFCV) calculated with this method shows that MFCV in DD patients (2.38 +/- .94 m/sec) is significantly slower than in 20 control children of the same age (3.24 +/- .53 m/sec). The distribution frequency of MFCV in all fibers tested in healthy children shows a Gaussian distribution (mode = 3.2 m/sec). In DD patients the distribution frequency is bimodal with spikes at 1.2 and 2.4 m/sec. Significant decrease in minimum propagation velocity and increased SD values were other striking results in patients with DD. Slowing and large variation in MFCV were significantly correlated with some findings in a coaxial needle electromyogram, such as long polyphasics and motor unit potentials followed by satellites. Satellites might arise from atrophic muscle fibers with slow conduction velocity. The results of MFCV were supported by the pathologic findings in DD subjects. The reported method for MFCV in situ is reliable and easy to apply in children, has merit for testing the size and function of muscle fiber, and helps to explain some electropathologic features in DD patients.
Cruz Martinez
A
A
Section of Electromyography, Hospital La Paz, Madrid, Spain.
Lopez Terradas
J M
JM
D002648:Child; D002675:Child, Preschool; D004558:Electric Stimulation; D004576:Electromyography; D004594:Electrophysiology; D006801:Humans; D008297:Male; D009136:Muscular Dystrophies / Q000503:physiopathology*; D009469:Neuromuscular Junction / Q000502:physiology*; D009435:Synaptic Transmission