Changes in short afferent inhibition during phasic movement in focal dystonia

• Published in: Muscle & nerve Vol. 37; no. 3; pp. 358 - 363
• Main Authors: Richardson, Sarah Pirio, Bliem, Barbara, Lomarev, Mikhail, Shamim, Ejaz, Dang, Nguyet, Hallett, Mark
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01.03.2008; Wiley
• Subjects: Adult; Afferent Pathways - physiology; Afferent Pathways - radiation effects; Analysis of Variance; Biological and medical sciences; Diseases of striated muscles. Neuromuscular diseases; Dystonic Disorders - physiopathology; Electric Stimulation - methods; Electromyography - methods; Evoked Potentials, Motor - physiology; F-wave; Female; focal hand dystonia; Fundamental and applied biological sciences. Psychology; Hand; Humans; Male; Medical sciences; Middle Aged; Motor control and motor pathways. Reflexes. Control centers of vegetative functions. Vestibular system and equilibration; Movement - physiology; Neural Inhibition - physiology; Neural Inhibition - radiation effects; Neurology; Reaction Time - physiology; Reaction Time - radiation effects; short afferent inhibition; surround inhibition; transcranial magnetic stimulation; Transcranial Magnetic Stimulation - methods; Vertebrates: nervous system and sense organs; Spinal cord; F-wave; Central nervous system; Electrophysiology; Dorsal interosseous muscle; Involuntary movement; focal hand dystonia; Rest; short afferent inhibition; Neurological disorder; Human; Nervous system diseases; Transcranial magnetic stimulation; surround inhibition; Electrical stimulus; Motor control; Hand; Abductor digiti minimi muscle; Cerebral disorder; Striated muscle disease; Central nervous system disease; Motor evoked potential; Dystonia; F wave; Extrapyramidal syndrome
• ISSN: 0148-639X; 1097-4598
• DOI: 10.1002/mus.20943

Impaired surround inhibition could account for the abnormal motor control seen in patients with focal hand dystonia, but the neural mechanisms underlying surround inhibition in the motor system are not known. We sought to determine whether an abnormality of the influence of sensory input at short latency could contribute to the deficit of surround inhibition in patients with focal hand dystonia (FHD). To measure digital short afferent inhibition (dSAI), subjects received electrical stimulation at the digit followed after 23 ms by transcranial magnetic stimulation (TMS). Motor evoked potentials (MEPs) were recorded over abductor digiti minimi (ADM) during rest and during voluntary phasic flexion of the second digit. F‐waves were also recorded. We studied 13 FHD patients and 17 healthy volunteers. FHD patients had increased homotopic dSAI in ADM during flexion of the second digit, suggesting that this process acts to diminish overflow during movement; this might be a compensatory mechanism. No group differences were observed in first dorsal interosseous. Further, no differences were seen in the F‐waves between groups, suggesting that the changes in dSAI are mediated at the cortical level rather than at the spinal cord. Understanding the role of these inhibitory circuits in dystonia may lead to development of therapeutic agents aimed at restoring inhibition. Muscle Nerve, 2007