Diagnostic tests in myasthenia gravis: an overview

Response to suxamethonium in a myasthenic patient during remission

A cumulative dose followed by an infusion was used to determine the dose response to suxamethonium in a patient with diagnosed myasthenia gravis who was in true remission (asymptomatic while receiving no therapy). The ED50 and ED90 values for suxamethonium were 0.08 mg/kg and 0.20 mg/kg, and an infusion rate of 3.2 mg/kg/hour was required to maintain a 90-95% depression of the single twitch response as monitored by integrated electromyography. These values are within the range for normal patients, and we conclude that myasthenic patients during a true remission may not demonstrate resistance to suxamethonium.

The effect of anti-thymocyte antiserum in progressive myasthenia gravis

The therapeutic effect of goat anti-human thymocyte antiserum globulin (ATG) was assessed in ten patients with myasthenia gravis. Five patients had undergone prior thymectomy. All subjects had far-advanced, debilitating and progressing disease poorly responsive to classic anticholinesterase therapy. Prolonged, low dose ATG therapy was used with 1.0-2.6 grams/protein administered intramuscularly over a 28-73 period. Depression of cellular immunity was observed with anti-thymocyte antiserum was more profound in patients with a prior thymectomy. Therapeutic responses of varying degrees were noted in 8 out of 10 patients. Completion of a course of ATG and discontinuation of the drug did not lead to acute relapse states. Follow-up examinations for over five years have been maintained. A mean remission period of approximately two years was observed. It is suggested that this therapy deserves further evaluation. Subjects with prior thymectomy and progressive disease may represent the most ideal candidates.

The regional curare test in myasthenia gravis

30 subjects without disturbance of neuromuscular transmission and 18 patients with myasthenia gravis were used in conducting the regional curare test. The adductor pollicis and the hypothenar muscles were studied with the 3/sec stimulation test. With three different dosages of curare one could find no reliable border between "normal" and "pathological". In the patients with myasthenia no definite relation could be found between the findings with the regional curare test and the clinical picture. The curare concentration reaching the muscle is probably quite variable from case to case as regards diffusion and volume in the tissue. The 3/sec stimulation test with registration from the deltoid muscle, and in certain cases the systemic curare test, appear more suitable than the regional curare test for routine diagnosis as well as indication for thymectomy. But for cases of ocular myasthenia showing no further weakness by the systemic curare test, the regional curare test can be put to use. The advantage lies in the higher concentration of curare which can thereby be brought to the muscle. The precautionary measures should be similar to those taken with the systemic curare test.

The results to be expected from electrical testing in the diagnosis of myasthenia gravis

The purpose of this study was to derive numerical data concerning the probability of diagnosing myasthenia gravis by electrical tests, employing repetitive stimulation of motor nerves. This was done by recording the compound muscle action potential (CMAP) from 80 patients with clear-cut myasthenia gravis, using a number of different, reportedly useful, testing techniques. In 95% of these patients, the diagnosis could be documented by the careful application of rather simple methods, providing several muscles, including a proximal one such as deltoid, were studied.

[Morphology of the motor endplate. Aspects of interest in neurology]

Os AA fazem revisão sobre a unidade motora em seu aspecto morfológico, fisiológico e farmacológico como base para o estudo e tratamento da miastenia grave e da síndrome miastênica. Estudos eletromiográficos, farmacológicos e eletrofisiológicos, realizados por diversos autores, determinam características especiais que definem a miastenia grave e a síndrome miastênica. Certos sinais e sintomas, comumente observados em casos de envenenamento por elapídeos, são semelhantes aos causados por drogas bloqueadoras neuromusculares.