ELECTROMYOGRAPHIC CHANGES IN SKELETAL MUSCLE DUE TO TETANUS TOXIN

¹ Department of Pharmacology and Therapeutics, Graduate School and Stritch School of Medicine of Loyola University, Chicago, Illinois

Local tetanus was produced in the tibialis anticus muscles of rabbits by intramuscular injection of a minute quantity of tetanus toxin. Electromyographic data were collected from the affected muscles at various intervals of time following the injection of the toxin and were compared with similar data obtained from normal muscles and muscles it chronic denervation. The muscle in early local tetanus (1 to 5 days) exhibited a state of unremitting stiffness and hyper-reflexia with a high degree of normal motor unit type of electrical activity in the muscle. As the local tetanus progressed (5 to 8 days) the EMG features changed. Instead of a large number of normal motor unit potentials, polyphasic potentials, positive sharp waves, and occasional fibrillation potentials were the major findings. With further progress of local tetanus (10 to 35 days) the electromyogram consisted entirely of fibrillation potentials which were identical in every respect to those of chronic denervation. As further time progressed the EMG features showed a reverse sequence, i.e., the spontaneous fibrillation potentials were replaced by positive sharp waves, polyphasic potentials, and finally by motor unit potentials. These findings were analogous to those obtainable during regeneration following denervation by nerve section. Thus it is shown that tetanus toxin gives rise to "pharmacological fibrillation potentials" in the skeletal muscle of rabbits and that this phenomenon is reversible.