A new method for the estimation of the number of motor units in a muscle: 1. Control subjects and patients with myasthenia gravis

Abstract

A new method, incorporating on-line computer analysis, is described for the estimation of the numbers of motor units in human muscle. The results obtained in the extensor digitorum brevis muscle in normal subjects and patients with myasthenia gravis are presented. These indicate that the numbers of motor units in that muscle in patients with myasthenia gravis are within the normal range, in contrast with the reduction in numbers reported by other workers using a different technique. Evidence is presented to suggest that the discrepancy in these results is due to increased sensitivity and discrimination of the computerized method. Several hypotheses on the aetiology of a number of neuromuscular diseases, based on the results of the other method, may require reevaluation.

Computer method for the analysis of evoked motor unit potentials. 2. Duchenne, limb-girdle, facioscapulohumeral and myotonic muscular dystrophies.

“…Figure 3 does, however, show that there has been a very small increase in the percentage of low and high amplitude MUPs. We have reported normal motor unit numbers in these patients (Ballantyne and Hansen, 1974c). This alteration in MUP parameters is probably the electrophysiological reflection of a pathological remodelling of the motor units.…”

“…Histological studies (Buchthal et al, 1960;Adams, 1974) indicate a reduction in the number of muscle fibres in the muscles in Duchenne dystrophy. We have reported normal numbers of motor units in the EDB muscles of these patients (Ballantyne and Hansen, 1974c). There is therefore a reduction in the number of muscle fibres in each motor unit.…”

“…Motor unit counts from the EDB muscles of these patients have been reported (Ballantyne and Hansen, 1974c).…”

“…Recently, Tate and Westerman (1973) reported multiple innervation of muscle fibres in the soleus muscle of the cat during reinnervation. Buller (1974) (McComas et al, 1971a;Ballantyne and Hansen, 1974c). These are not the expected findings in a primary myopathy.…”

“…TECHNIQUES The composition and placement of the surface recording electrode over the EDB muscle, the properties of the stimulating electrodes over the anterior tibial nerve at the ankle, and details of the rate and strength of stimulation used to evoke MUPs have been described previously (McComas et al, 1971b;Ballantyne and Hansen, 1974a). The description of the amplification and display systems and of the computer handling of data for the isolation of individual MUPs has been presented (Ballantyne and Hansen, 1974b).…”