BOTULINUM TOXIN TREATMENT OF MUSCLE CRAMPS - A CLINICAL AND NEUROPHYSIOLOGICAL STUDY

Botulinum toxin is now widely used in the treatment of several hyperki netic movement disorders. To evaluate its efficacy in treating muscle cramping syndromes, we studied clinical and neurophysiological variabl es before and after botulinum toxin injections into calf muscles and s mall flexor muscles of the foot in patients with an inherited benign c ramp-fasciculation syndrome. At each assessment the clinical severity of cramp was scored and the cramp threshold frequency was measured wit h repetitive electrical peripheral nerve stimulation. Botulinum toxin injection significantly lowered our patients' clinical cramp severity scores (mean +/- SD: before, 3.80 +/- 0.44; after, 1.40 +/- 0.54), lef t muscle strength unchanged and significantly increased their cramp th reshold frequencies (before, 4.22 +/- 2.26 Hz; after, 10.0 +/- 3.74 Hz ). The clinical benefit induced by botulinum toxin lasted about 3 mont hs. Botulinum toxin injections also significantly reduced fasciculatio n potentials in relaxed muscles (before, 0.86 +/- 0.19 fasciculations/ sec; after, 0.45 +/- 0.11 fasciculations/sec). These findings show tha t local intramuscular injections of botulinum toxin provide effective, safe, and long-lasting relief of cramps possibly by reducing presynap tic cholinergic stimulation of motor nerve terminals and by impairing the input/output function of intrafusal and extrafusal motor end plate s.