Spinal and cortical inhibition in huntington's chorea

• Published in: Movement disorders Vol. 15; no. 5; pp. 938 - 946
• Main Authors: Priori, Alberto, Polidori, Luigi, Rona, Sabine, Manfredi, Mario, Berardelli, Alfredo
• Format: Journal Article
• Language: English
• Published: New York John Wiley & Sons, Inc 01.09.2000; Wiley
• Subjects: Adult; Aged; Biological and medical sciences; Case-Control Studies; Cortical stimulation; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Electric Stimulation; Electromyography; Female; H-Reflex; Humans; Huntington Disease - physiopathology; Hyperkinesia; Magnetics; Male; Medical sciences; Middle Aged; Models, Neurological; Motor Cortex - pathology; Motor Cortex - physiopathology; Neural Inhibition; Neural Pathways - physiopathology; Neurology; Presynaptic Terminals; Reciprocal inhibition; Spinal Cord - pathology; Spinal Cord - physiopathology; Human; Nervous system diseases; Cerebral cortex; Spinal cord; Pathogenesis; Huntington disease; H-Reflex; Exploration; Cerebral disorder; Genetic disease; Transcranial route; Electrodiagnosis; Reciprocal inhibition; Central nervous system disease; Magnetic stimulus; Adult; Degenerative disease; Motor evoked potential; Extrapyramidal syndrome
• ISSN: 0885-3185; 1531-8257
• DOI: 10.1002/1531-8257(200009)15:5<938::AID-MDS1026>3.0.CO;2-Q

In this article we studied spinal and cortical inhibitory mechanisms in patients with Huntington's disease. To evaluate spinal cord inhibitory circuitries, we assessed reciprocal inhibition between antagonist forearm muscles and the recovery cycle of the H reflex in the flexor carpi radialis. Patients showed a significant decrease in the presynaptic phase of reciprocal inhibition reaching a minimum at the conditioning‐test interval of 20 msec and an abnormal facilitation of the test H reflex at the conditioning test interval of 40 to 60 msec. Throughout its time course (10–200 msec), the H reflex recovery cycle showed a more prominent facilitation in patients than in control subjects. To assess whether the observed pathophysiological abnormalities might have arisen from an abnormal motor cortical excitability, we examined the recovery cycle of the motor potentials evoked by paired transcranial magnetic stimuli. We found that the inhibitory mechanisms controlling motor cortical excitability were normal. An interpretation of the spinal cord abnormalities is that the intrinsically normal but deafferentated motor cortex in Huntington's disease partly loses its inhibitory control, thus disinhibiting spinal cord circuitry. Our findings from paired transcranial magnetic stimulation suggest that cortical motor areas are not hyperexcitable in Huntington's disease. Hence, the postulated thalamocortical overactivity in experimental models of Huntington's disease needs to be reappraised.