Effects of botulinum toxin type A on vibration induced facilitation of motor evoked potentials in spasmodic torticollis.
OBJECTIVE
It has not been clarified if botulinum toxin (BTX) injection leads to muscle spindle dysfunction in man. This study aimed to test the hypothesis that BTX application reduces the facilitation of a magnetic evoked response (MEP).


METHODS
We used the vibration induced facilitation of an MEP of the sternocleidomastoid muscle (SCM) as a surrogate marker for muscle spindle function in 20 healthy subjects and 10 patients with idiopathic rotational torticollis in whom BTX was injected unilaterally.


RESULTS
The increase in the amplitude and area of the MEPs in the clinically not affected and untreated SCM of the patients did not differ significantly from the controls. At baseline, the vibration induced increase in the affected SCM of the patients was significantly lower than in the control group. Six weeks after BTX application, the observed facilitation decreased significantly (amplitude and area: p<0.001) when compared with baseline values. Twelve weeks after BTX application, facilitation showed an increase in the values of the amplitude (p<0.001), but not of the area when compared with the six week examination.


CONCLUSIONS
We demonstrated that the vibration induced MEP facilitation in the SCM of patients with torticollis significantly decreased six weeks after BTX application and again increased after 12 weeks in part when looking at MEP amplitude. This observation is suggestive of denervation and reinnervation of the muscle spindles after BTX injection.
Department of Neurology, University of Mainz, Langenbeckstr. 1, D 55101, Germany. urban@neurologie.klinik.uni-mainz.de
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Urban
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Rolke
D000328:Adult; D000368:Aged; D019274:Botulinum Toxins, Type A / Q000009:adverse effects / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D019054:Evoked Potentials, Motor / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006801:Humans; D007273:Injections, Intramuscular; D008297:Male; D008875:Middle Aged; D009121:Muscle Denervation; D009334:Neck Muscles / Q000187:drug effects / Q000294:innervation; D009416:Nerve Regeneration / Q000187:drug effects / Q000502:physiology; D009465:Neuromuscular Agents / Q000009:adverse effects / Q000627:therapeutic use*; D014103:Torticollis / Q000188:drug therapy* / Q000503:physiopathology; D014732:Vibration
D009465:Neuromuscular Agents; D019274:Botulinum Toxins, Type A