Myotonia Congentia
From Wikipedia, the free encyclopedia
A rare congenital disease, when the patient starts to perform a voluntary movement, the muscle are thrown into a state of spasm which gradually passes off; thus if he yawns the mouth remains open for some time. As the movement is repeated the muscles become more supple. If the muscle is stimulated electrically, contraction persists for a considerable time after stimulation is discontinued, An interesting strain of goat has been discovered in the U.S.A. suffering from a condition indistinguishable from human myotonia; as a result the condition can be examined experimentally. The muscles are extremely sensitive to mechanical stimulation; tapping, for instance, produces a long lasting contraction which is due to a long lasting tetanus in groups of muscle fibres, accompanied by normal action potentials. The response is obtained after cutting the motor nerve. The response of the muscle to a single motor nerve stimulus is not a twitch but is repetitive, and the tension is correspondingly greater than in normal animals. At the end of a bout of stimulation at a rate of 50 per second (to produce a tetanus), the muscle remains tetanically contracted as it does after sudden exertion in this disease. The abnormal sensitivity to mechanically stimulation is unaffected by curare or complete degeneration of the motor nerve ending; it is, however, progressively reduced by bouts of stimulation at low rates, e.g. 5 per second, sensitivity to intra-arterially injected acetylcholine is unchanged, but the duration of the response is increased. Sensitivity to injected potassium salts is however far greater. But to changes in the excitability of the muscle fibres themselves. Quinine has proved clinically; and it similarly relieves the myotonic condition in goat.
Ref
Brown and Harvey, J. physiol., 1939, 96, 11p.
Kolb, Johns Hopk. Hosp. Bull., 1939, 63, 221.
Denny-Brown and Nevin, Brain, 1941, 64, 1.
