title: Afferent and efferent excitabilities of the transcortical loop in patients with dentatorubral-pallidoluysian atrophy.
abstract: To evaluate the excitabilities of the transcortical loop in patients with dentatorubral-pallidoluysian atrophy (DRPLA), we studied somatosensory evoked potentials (SEPs) and evoked EMG responses (V1 and V2) in 10 patients and age-matched controls. In addition, the facilitatory effects of somatosensory inputs on motor evoked potentials (MEPs) were studied in four patients and controls. We observed attenuated or prolonged cervical and subcortical potentials and prolonged middle latency components of SEPs. The amplitudes of V2 in patients were significantly lowered compared to those in the controls, while the amplitudes and latencies of V1 were similar between the two groups. Since V2 was considered as a transcortical reflex, our results suggest reduced excitabilities of the afferent pathway of the transcortical loop in patients with DRPLA. Median nerve stimulation (MNS) 25 to 30 ms preceding transcranial magnetic stimulation (TMS) facilitated MEPs in the thenar muscle in two of the four patients and in the controls. The facilitation of MEPs by MNS tended to be independent of the reduction in V2. Such a result suggests that different neural mechanisms elicit V2 and facilitate MEPs following peripheral nerve stimulation, although further studies are needed. The combination of SEPs, evoked EMG responses and MEPs may be a useful technique to detect abnormalities of input and output coordinations of the transcortical loop.
authors.affiliation: Third Department of Internal Medicine, Kagawa Medical University, 1750-1, Ikenobe, Miki-cho, Kita-gun, Kagawa, Japan. touge@kms.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Touge
authors.forename: N
authors.initials: N
authors.lastname: Ichihara
authors.forename: T
authors.initials: T
authors.lastname: Ishibashi
authors.forename: M
authors.initials: M
authors.lastname: Ikeguchi
authors.forename: I
authors.initials: I
authors.lastname: Sasaki
authors.forename: H
authors.initials: H
authors.lastname: Takeuchi
mesh_terms: D000293:Adolescent; D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D006801:Humans; D008280:Magnetics; D016555:Matched-Pair Analysis; D008475:Median Nerve / Q000502:physiology; D008875:Middle Aged; D020191:Myoclonic Epilepsies, Progressive / Q000235:genetics / Q000503:physiopathology*; D012021:Reflex, Abnormal / Q000502:physiology