LONG-LATENCY REFLEXES OF HAND MUSCLES IN IDIOPATHIC FOCAL DYSTONIA AND THEIR MODIFICATION BY BOTULINUM TOXIN

Long-latency reflexes (LLR) in thenar muscles were elicited by electri cal median nerve stimulation in 34 patients with idiopathic focal dyst onia and 20 healthy control subjects. Twenty-seven patients had cervic al dystonia and seven patients had upper limb dystonia. In about one-q uarter of all patients the early LLR (LLR 1, occurring at similar to 4 0 ms) was abnormal with either increased amplitudes or only unilateral occurrence, mostly on the clinically affected side. Later responses ( LLR 2, occurring at similar to 50 ms) were obtained bilaterally in all controls but were reduced or absent in some patients, mostly on the c linically affected sine. In 12 dystonia patients, LLR studies were als o performed after clinically effective injection of botulinum toxin. F ollowing botulinum toxin treatment there was a significant reduction o f LLR 2 amplitudes on the clinically affected side. Our findings sugge st a differential involvement of LLR generators in idiopathic dystonia with an antagonism between LLR 1 and LLR 2 on the affected sides. We propose that the reduction of the LLR 2 response may arise from overac tivity of the supplementary motor area, confirming the current concept that dystonia results from cortical overflow due to disinhibited thal amocortical pathways projecting to the supplementary motor area. In ad dition, the dystonic motes pattern seems open to afferent modification s induced by peripheral botulinum toxin treatment.