Pathophysiology of Dystonia

Transcription

1 Continuing Medical Education 84 Pathophysiology of Dystonia Rou-Shyan Chen Abstract- Dystonia is a diverse movement disorder characterized by involuntary muscle co-contraction of the agonist and antagonist, which may cause twisting and repetitive movements or abnormal posture. Dystonia is the least understood movement disorder associated with the basal ganglia dysfunction. While dysfunction of cortico-striatal-thalamo-cortical motor circuits is likely to play a fundamental role in the pathophysiology of dystonia, the disorder does not easily fit into the hypokinetic or the hyperkinetic category of basal ganglion diseases. There was evidence of widespread impairment of the inhibition involving multiple levels of the nervous system. There was also significant data to support the notion that the sensory function and sensorymotor integration were debit in patients with dystonia. The reciprocal inhibition curves between the forearm muscles were abnormal at the spinal cord level, as well as the blink reflex recovery curves at the brain stem level. The motor cortex excitability was enhanced while the transcranial magnetic stimulation. The dystonia showed decreased inhibition of the intracortical inhibition and facilitation and short cortical silent period. The pre-movement gating of the somatosensory evoked potentials and the somatosensory homunculus were abnormal in dystonia. This review provides an overview of the recent studies of the pathophysiology of dystonia, with an emphasis on the cortical plasticity. The possible beneficial effects of the transcranial magnetic stimulation (TMS) and repetitive transcranial magnetic stimulation (rtms) with new paradigm are also discussed. Key Words: Dystonia, Electrophysiology, Transcranial magnetic stimulation, Cortical excitability. Movement Disorders Section, Department of Neurology, Chang Gung Memorial Hospital, Taipei, Taiwan. Received December 29, Revised January 10, Accepted May 9, Reprint requests and correspondence to: Rou-Shyan Chen, MD. Movement Disorders Section, Department of Neurology, Chang Gung Memorial Hospital. No. 199, Tun-Hwa North Road, Taipei, Taiwan. cerebrum@ms13.hinet.net

2 85 (reciprocal inhibition curve) (blinking reflex recovery curve) (motor cortex) (intracortical inhibition and facilitation curve) (motor cortex excitability) (decreased duration of silent period) (abnormal pre-movement gating of somatosensory input) (abnormal somatosensory homunculus in dystonia) (transcranical magnetic stimulation) Acta Neurol Taiwan 2005;14:84-93 (dystonia) movement) posture) (1) (electromyogram) (abnormal (twisting) (repetitive (2,3) cerebrum@ms13.hinet.net

3 86 (generalized dystonia) dystonia) (3) (overflow phenomenon) (4) (mirror movement) (5) (5) (1) (2) (3) ( ) (4) (1) primary dystonia; (2) dystonia-plus syndrome; (3) heredodegenerative dystonia; (4) secondary dystonia (sensory trick) (Botulinum toxin-a) (sterenocleidomastoid muscle (6) (6) SCM) (1) (action dystonia) (2) (task-specific (extensor type) (anterior trapezius) (flexor type) I. a. b.. (7) II. a. b. c. d. e. III. a. b. (1) (2) (i) (ii) (iii) (iv) 4 (i) (ii) (7) (repetitive move- DYT1 gene (8) Kaji R 1995 ment) Ia lidocaine (9) Kaji (10)

4 87 (C) Byl NN 1996 (11) (A) inhibition in dystonia) (Decreased Rothwell curve) (16) (reciprocal inhibition (12-14) (15) (writer s cramp) (spasmodic dysphonia) (spasmodic torticollis) (17- (blepharospasm) 20) - (center-surround inhibition) surround-inhibition ( ) (19) ( ) (B) (A) curve) (Blinking reflex recovery.

5 88 (interneuronal inhibition) ( ) (21) (motor cortex) (enhanced motor cortex excitability) (motor evoked potential) ( 1ms 5ms) ( ) Robert Chen (13,14,22) (silent period) center-surround inhibition (23) Leocani 2000 Leocani (reciprocal inhibition curve) ( ) co-contraction center-surround inhibi- (putamen) D2 tion mechanism ( ) (basal ganglion) (24) - - -

6 89 Normal controls Spasmodic dysphonia before BOTX-A % of area (conditioned / unconditioned). (blinking reflex recovery curve of spasmodic dysphonia) R2 R2 ISI (msec) (indirect pathway) (25) Liepert 1998 (base line) (29) (26) (27-31) Kaji R, Murase N, Nakamarak, (B) Urushihara R, Asanuma K (somatosen- Bara-Jimenez W (source localization) sory evoked potential SSEP) (27,28) Abbruzzese G PAS (paired associated stimulation) motor evoked potential) (amplitude of 200 (abnormal pre-movement gating of somatosensory input) (brisk wrist extension) SEP N30 P22

7 90 conditiond MEP/unconditioned MEP(%). (intracortical short latency inhibition and facilitation curve) (1, 2, 3, 4 ) Iinter-stimuli-interval (msec) ( amplitude of the motor evoked potentials) N30 P22 SEP (SEP generator) (synchronized) SEP (gating phenomenon) (transcranial magnetic stimulation TMS) ( TMS) (32) (33) (pallidum) (1) TMS (cortical plasticity) (2) TMS (abnormal premovement gating of sensory input) (C) (cortical excitability) (cortical plasticity) TMS 10 2 functional neuroimage) TMS (activation

8 91 18 (positron emission tomography (PET) of 18-fluorodeoxyglucose (FDG)) FDG-PET Eidelberg (premotor cortex) (supplementary motor area) (34,35) 15 Theta burst stimulation (TBS) rtms (long-term potentiation longterm depression) (cortical plasticity) TBS rtms (H215O PET) Ceballos-Baumann (frontal association projection area ) pre-motor cortex (PMC) dorsolateral prefrontal cortex (DLPFC) (36,37) PMC DLPFC (transcranical magnetic stimulation TMS) TMS (repetitive TMS rtms) (38-42) r TMS ( 1Hz) 5 r TMS ( 5Hz) (41,42) (40) (TMS) (TBS) rtms (38,43,44) Murase 85% 0.2Hz 250 PMC (pre-motor cortex) (45) Rothwell JC (45) 2 10 YZ Huang r TMS (46) rtms 50Hz rtms Hz YZ Huang 1. Fahn S, Bressman SB, Marsden CD. Classification of dystonia. Adv Neurol 1998;78: Cohen LG, Hallett M. Hand cramp: clinical features and electromyographic patterns in a focal dystonia. Neurology 1998;38: Rothwell JC, Obeso JA, Day BL, et al. Pathophysiology of dystonias. Adv Neurol 1983;39: Fahn S, Marsden CD, Calne DB. Classification and investigation of dystonia. Movement Disorder 2. In: Marsden CD, Fahn S, eds. London: Batterworths, 1987: Sheehy MP, Marsden CD. Writer s cramp: a focal dystonia.

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