Botulinum toxin is now widely used in the treatment of several
hyperkinetic movement disorders. To evaluate its efficacy in treating muscle cramping syndromes, we studied clinical and neurophysiological variables before and after
botulinum toxin injections into calf muscles and small flexor muscles of the foot in patients with an inherited benign
cramp-fasciculation syndrome. At each assessment the clinical severity of
cramp was scored and the
cramp threshold frequency was measured with 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), left muscle strength unchanged and significantly increased their
cramp threshold frequencies (before, 4.22 +/- 2.26 Hz; after, 10.0 +/- 3.74 Hz). The clinical benefit induced by
botulinum toxin lasted about 3 months.
Botulinum toxin injections also significantly reduced
fasciculation potentials in relaxed muscles (before, 0.86 +/- 0.19
fasciculations/sec; after, 0.45 +/- 0.11
fasciculations/sec). These findings show that local
intramuscular injections of
botulinum toxin provide effective, safe, and long-lasting relief of
cramps possibly by reducing presynaptic
cholinergic stimulation of motor nerve terminals and by impairing the input/output function of intrafusal and extrafusal motor end plates.