Six patients with congenital myotonia and 4 patients with myotonic dystrophy have been examined clinically before and after the administration of N-propyl-ajmalin, an alkaloid frequently used as a cardiac antiarrhythmic drug. All patients but one reported a good to moderate improvement of their myotonic muscle stiffness. This was verified by measuring the time the patients needed to ascend a flight of stairs and by recording the speed of opening the hand. The amplitude of the compound muscle action potential decreased during repetitive nerve stimulation in myotonic patients. This decrease was not influenced by N-propyl-ajmalin. It seems to be due to the increased after-depolarization observed in myotonic fibres which causes partial inactivation of the Na-carrying system. From one patient a muscle biopsy was taken and intracellular potentials were measured with a microelectrode. Almost all muscle cells investigated showed myotonic activity which was completely abolished by addition of 10(-5) g/ml N-propyl-ajmalin to the bathing fluid. The development and duration of "warm-up" is illustrated and a possible electrophysiological basis is discussed.
Antibodies (Ab) to acetylcholine receptors ( AchR) are instrumental in bringing about the neuromuscular defect in myasthenia gravis (MG) . The demonstration of Ab by immunoprecipitation assay proved to be highly specific, of great diagnostic value, and in good correlation to clinical improvement in MG patients on plasma exchange therapy.l, Only little information is available in the long term correlation between intraindividual AB titers and clinical course.2 This study presents a group of 99 MG patients (41 male, 58 female; mean age 45, five years) followed up for 36 months, using a new, simple and reproducible MG-Score (see TABLE 1 ) and serial measurements of Ab titers by a modified immunoprecipitation assay.3To calculate the correlation of Ab titer and clinical course, relative changes of MG-Score in individual patients and the differences in normalized Ab titers of the identical interval were plotted against each other. Each interval of usually one to two months was analyzed separately. (Bivariate plotting program BMDP6D by H.C.S.F. U.C.L.A. 1977, adapted to a Siemens 4004/151 computer.) The correlation is calculated in different groups of MG patients, referring to age, sex and duration as well as to MG patients with mild (MG-Score <1.0) and marked (MG-Score >1 .O j disease.We found a high correlation between Ab titer and clinical course in serial measurements of patients with moderate and marked MG. In contrast there was no correlation in patients with mild disease. No influence of age and sex of MG-patients or duration of the disease upon this correlation could be demonstrated. Long-term observations of individual patients generally showed a close correlation between MG-Score and serially determined Ab titer. In about 10% of the severely affected MG patients however rising Ab titers could be demonstrated without immediate increase in MG-Score. In those patients deterioration could be detected within three weeks to three months. The MG-Score used in this study is a simple and reliable tool for the clinical follow-up of MG patient as well as for long term investigations. From our * Correspondence address for U. A. Besinger includes Moehlstrasse 28 8000 Munich
The effects of corticotropin (ACTH) and the polypeptide fragment ACTH 4-10 on neuromuscular transmission were studied in rat phrenic nerve-diaphragm preparations in vitro. ACTH decreased the quantum content of end-plate potentials (epps) and increased the transmission failure rate. The frequency of miniature end-plate potentials (mepps) was increased. The results indicate that ACTH acts directly on the presynaptic terminal. The findings could explain the transient decrease in muscle strength often observed during corticotropin therapy for myasthenia gravis, and they suggest that the therapeutic effcct of ACTH is indirectly mediated. The only marked effect produced by the ACTH fragment was an increase in the mepp frequency; quantum content and failure rate of epps remained unchanged. Since ACTH 4-10 is unable to stimulate cortisone release, its clinical efficacy seems unlikely. Birnberger
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