Single fiber electromyogram in myasthenia gravis and other neuromuscular diseases
Nogués, M.A.; Rivero, A.; Stalberg, E.
Medicina 51(4): 307-314
1991
ISSN/ISBN: 0025-7680 PMID: 1668291 Document Number: 371337
Single fibre electromyography (SFEMG) has been used to study neuromuscular transmission and the degree of reinnervation in patients with myasthenia gravis (MG) (n = 70); Lambert-Eaton syndrome (n = 3); myopathies (n = 8); motor neuron disease (n = 4) and peripheral neuropathies (n = 3) (Table 1). An automatic method was used to calculate neuromuscular jitter by means of a PC computer, a TECA TD 20 electromyograph and a jittermeter. Twenty pairs of potentials were selected from the extensor digitorum communis muscle for analysis using a trigger unit and a delay line. Mean jitter and percentage of pairs with normal and abnormal jitter were calculated (Figs. 1 and 2). MG patients showed pairs with normal (Fig. 3) and other with abnormal jitter and intermittent blocking (Fig. 4). Abnormalities were found in 72% of patients with ocular MG, in 95% with mild generalized MG, in 93% with moderate generalized MG and in 100% of severe MG cases (Table 2), (Fig. 5). There was a significant correlation between patient disability and jitter values (Fig. 6). The method was useful for the follow-up during immunosuppressant treatment (Fig. 7). Patients with other myopathies showed normal or mildly increased jitter and increased fibre density. The most common abnormality in patients with neurogenic conditions was increased fibre density, which ranged from 2.1 to 4.3 (Figs. 8 and 9). The method used showed high sensitivity for the detection of neuromuscular transmission defects. In some cases an abnormal jitter was found even before the appearance of transmission block and therefore it was possible to find abnormalities in clinically normal muscle.