Contractile properties of the abductor digiti minimi muscle in paramyotonia congenita

Abstract

SYNOPSIS In two subjects with paramyotonia congenita the isometric torque generated by the abductor digiti minimi and the surface EMG recorded over ADM decreased during prolonged or repetitive contractions, whether these were voluntarily or electrically induced. Isometric twitch times did not alter significantly during this muscle fatigue. Cooling greatly accelerated the fatiguing process. It is suggested that this local muscle weakness is due to a progressive decrease in excitability of the muscle cell membrane.

An analysis of myotonia in paramyotonia congenita

“…6; compare with Fig. 4, Burke et al, 1974b). Surface temperature decreased from 34-35°to between 21°C and 28°C in different experiments.…”

“…2B), so that relaxation on cessation of muscle contraction appeared to be rapid and smooth ( Fig. 2A, see also Figs 2 and 3 in Burke et al, 1974b). Repeated trains of 2-5 s duration similarly did not induce visible evidence of myotonia.…”

“…Fig. 1, Burke et al, 1974b). If voluntary contraction was alternated with tetanic contraction, myotonia could be elicited with the former but not the latter.…”

“…mental session in a similarly afflicted 19 year old brother. These sessions provided data for this paper and a companion paper on muscular weakness (Burke et al, 1974b). Clinically the myotonia in both subjects was 'paradoxical'.…”

“…This paper analyses aspects of myotonia in two subjects with paramyotonia congenita with particular reference to the responses to repeated muscle contraction and to muscle cooling. Muscular weakness has been analysed in a companion paper (Burke et al, 1974b). METHODS Data were obtained from 13 experimental sessions in a 25 year old subject with classical paramyotonia congenita and were confirmed in a further experi-1 Some of these findings were reported to the 1974 meeting of the Australian Association of Neurologists.…”