Abnormalities of sensorimotor integration in focal dystonia - A transcranial magnetic stimulation study

It has been postulated that sensorimotor integration is abnormal in dystoni a, We investigated changes in motor cortical excitability induced by periph eral stimulation in patients with focal hand dystonia (12 patients with han d cramps) and with cervical dystonia (nine with spasmodic torticollis) comp ared with 16 age-matched normal controls, Motor evoked potentials (MEP) to focal (figure-of-eight coil) transcranial magnetic stimulation of the hand area were recorded from the right abductor pollicis brevis (APB), first dor sal interosseus (FDI), flexor carpi radialis and extensor carpi radialis mu scles. Changes of test MEP size following conditioning stimulation of the r ight median nerve (or of the index finger) at conditioning-test (C-T) inter vals of 50, 200, 600 and 1000 ms were analysed, Peripheral stimulation sign ificantly reduced test MEP size in the APE and FDI muscles of normal contro l and spasmodic torticollis patients, The inhibitory effect was larger upon median nerve stimulation and reached a maximum at the C-T interval of 200 ms, On the contrary, hand cramp patients showed a significant facilitation of test MEP size. This study suggests that MEP suppression following periph eral stimulation is defective in patients with focal hand dystonia, Central processing of sensory input is abnormal in dystonia and may contribute to increased motor cortical excitability.