SERIAL NEUROPSYCHOLOGICAL STUDIES OF INTRAMUSCULAR BOTULINUM-A TOXIN IN HUMANS

To characterize the time course of intramuscular botulinum toxin-induc ed paresis, we serially performed electrophysiological measurements an d recorded the sonographic size of an extensor digitorum brevis (EDB) muscle in 10 human subjects before and after injecting the EDB with 10 units of botulinum-A toxin. All EDB CMAPs decreased within 48 h, with peak decline at day 21 (8.3 +/- 3.1 mV to 3.0 +/- 0.9 mV). Decline of mean rectified voltage during maximal voluntary contraction of the ED B paralleled the change in CMAP amplitude. Average decrements to 2-Hz repetitive stimulation never exceeded 6% (day 42) and exercise failed to facilitate significantly CMAP amplitude. Atrophy peaked at day 42. The F-wave to M-wave ratio increased at day 2; silent periods did not change. Our findings confirm a primary peripheral action of the toxin, but a superimposed, transient central effect of the drug cannot be ex cluded. Intramuscular injections into EDB provide a useful model for s tudying chemodenervation effects. (C) 1994 John Wiley & Sons, Inc.