Tonic vibration reflex and muscle afferent block in writer's cramp

Abstract

Patients with focal dystonia take advantage of certain cutaneous or proprioceptive sensory inputs to alleviate their symptoms ("sensory trick"). We examined the effects of increasing muscle spindle activity by the tonic vibration reflex maneuver and decreasing it by intramuscular injection of lidocaine. The vibration was applied to the palm or the tendon of forearm muscles in 15 patients with writer's cramp and 15 age-matched normal subjects. In 11 patients, the vibration induced dystonic postures or movements typical of those seen during writing. Normal subjects showed either no response to the vibration or a gradually developing tonic vibration reflex only in the wrist and finger flexors, which produced visible movements with a significantly longer latency (12.5 +/- 6.7 seconds [mean +/- standard deviation]) than what was observed in the patients (2.7 +/- 2.5 seconds, p < 0.0001). Local injection of lidocaine (0.5%, 5-40 ml/muscle) attenuated the tendon reflex with relatively little effect on the M response. Injection into muscles with increased activity produced marked reduction of dystonic movements and significant clinical improvement in 13 patients, whereas injection into the other muscles had no effect. The clinical benefit lasted for 1 to 24 hours after injection. In 13 patients who had additional injections of 10% ethanol, which blocks sodium channels for a longer period than does lidocaine, the duration of action was prolonged to 5 to 21 days. These findings suggest that muscles causing dystonic movements have abnormal sensitivities to vibration at rest and that muscle afferents may play a pivotal role in producing dystonic movements.(ABSTRACT TRUNCATED AT 250 WORDS)

Botulinum toxin restores presynaptic inhibition of group Ia afferents in patients with essential tremor

“…An indirect action on the gamma loop is also consistent with evidence that lidocaine and alcohol, drugs that block the fusimotor drive, improve dystonia and tremor. 15,16,24 The indirect action on the gamma loop may summate with the effect of botulinum toxin on the extrafusal motor end-plate. The botulinum-induced reduction in the size of the M wave and of the H reflex can be explained by the toxin's blocking action on extrafusal nerve endings.…”

Muscle vibration: Different effects on transcranial magnetic and electrical stimulation

“…The cortical effects of MV in humans are known 13,18 and, in addition to spinal actions, could play a role in the modification of abnormal movements such as dystonia. 10,11 Therefore, we studied the possible cortical actions of MV in the late phase of MEP augmentation. We compared the effects of MV on MEPs following both TMS and transcranial electrical stimulation (TES), which allows for a differentiation between cortical and spinal actions.…”

Improved Dexterity after Chronic Electrical Stimulation of the Motor Cortex for Central Pain: A Special Relevance for Thalamic Syndrome

“…These results suggest that the declared improvement in motor performance may have something to do with improved somatosensory function and may be supported by experimental data showing that an ischemic lesion located either in the lateral thalamus (VPL, LP nuclei) or in the first somatosensory area interferes with motor cortex excitability [32,33]. The finding of improved proprioceptive ataxia (patients 2 and 4–10) is an additional argument in favor of this hypothesis, as is the finding that MCS may also dramatically improve poststroke dystonia (patients 1 and 3), a disease in which a primary dysfunction of lemniscal afferents to the somatosensory cortex has been proposed as a pathophysiological mechanism [34,35,36,37,38,39]. …”