Botulinum toxin changes intrafusal feedback in dystonia: a study with the tonic vibration reflex.
To investigate the possible role of botulinum toxin (BT-A) injection in reducing muscle afferent feedback, we evaluated electrophysiologically 10 right-handed patients with writer's cramp before and 3 weeks after treatment. The ratio between pre- and postinjection values of maximal M-wave (M-max), maximal voluntary contraction (MVC), and tonic vibration reflex (TVR) were measured in the injected muscles (wrist flexors or extensors). In all the subjects, BT-A injection reduced the TVR more than the M-max and MVC (mean ratio +/- SD: TVR, 0.24 +/- 0.22; MVC, 0.59 +/- 0.32; M-max, 0.68 +/- 0.24; P = 0.003). Long-term evaluation of 2 patients disclosed that, after 7 months, when some clinical benefits persisted, M-max and MVC had fully recovered, whereas the TVR was still depressed. This special sensitivity of the TVR to suppression by BT-A injection could be mediated by the chemodenervation of intrafusal muscle fibers, leading to a reduction in spindle inflow to the central nervous system during vibration. The action on intrafusal fibers could alter sensorimotor integration, thus contributing to the clinical benefits of BT-A injection.
Trompetto
Carlo
C
Dipartimento di Neuroscienze, Oftalmologia e Genetica, Università di Genova, Italia.
Currà
Antonio
A
Buccolieri
Alessandro
A
Suppa
Antonello
A
Abbruzzese
Giovanni
G
Berardelli
Alfredo
A
D000328:Adult; D000344:Afferent Pathways / Q000187:drug effects / Q000503:physiopathology; D000368:Aged; D001905:Botulinum Toxins / Q000494:pharmacology*; D004421:Dystonia / Q000503:physiopathology*; D005246:Feedback / Q000187:drug effects*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000187:drug effects*; D009119:Muscle Contraction / Q000187:drug effects*; D012018:Reflex; D014732:Vibration
D001905:Botulinum Toxins