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Neurology 05/2008; 70(16 Pt 2):1500-1. · 8.31 Impact Factor
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ABSTRACT: Writer's cramp, or focal hand dystonia, is characterized by involuntary coactivation of antagonist or unnecessary muscles while writing or performing other tasks. Recent studies of changes in cerebral blood flow during writing have demonstrated a reduction in the activation of the primary motor cortex (MC) and hyperactivity of the parts of frontal nonprimary motor areas. Therefore, any measures that decrease the activities of nonprimary motor areas like the premotor cortex (PMC) or supplementary motor area (SMA) might improve dystonic symptoms. We explore this possibility of acute effect, Nine patients with writer's cramp and seven age-matched control subjects were recruited. After the preliminary experiments, we used subthreshold low-frequency (0.2 Hz) repetitive transcranial magnetic stimulation (rTMS), which exerts an inhibitory action on the cortex. We compared the silent periods and computer-assisted ratings of handwriting before and after rTMS applied to the MC, SMA, or PMC. Stimulation of the PMC but not the MC significantly improved the rating of handwriting (mean tracking error from the target, P=0.004; pen pressure, P=0.01) and prolonged the silent period (P=0.02) in the patient group. This increased susceptibility of the PMC in dystonia suggests that lack of inhibition in the MC is secondary to the hyperactivity of PMC neurons. Further physiological studies disclosed that the amplitude of frontal N30 component was significantly increased after rTMS over the PMC in control subjects (p=0.014) but not in dystonic patients, and 99mTc-ECD SPECT showed the different activation pattern in between control subjects (Brodmann area 9 and 6 including PMC and prefrontal cortex) and patients (parietal and cerebellar cortices). These findings support the idea that cortical network pattern induced by rTMS is quite different in the two groups. It is not clear whether the activated areas seen in dystonia is due to primary or compensatory mechanism, but our findings sugge-
st the PMC plays an important role in the pathophysiology of dystonia. Additionally we showed 0.2 Hz rTMS over the premotor cortex was rather effective than ordinary 1 Hz stimulation over the MC, demonstrating that different frequency and stimulation site is to be explored in each disease depending on its own pathophysiology.
Complex Medical Engineering, 2007. CME 2007. IEEE/ICME International Conference on; 06/2007
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ABSTRACT: Multifocal motor neuropathy (MMN) is often misdiagnosed as motor neuron disease, especially when overt evidence of conduction block (CB) is lacking. Activity-dependent CB (ADCB), defined as transient CB induced by brief exercise, has been recently found in MMN but not in ALS.
To test the diagnostic utility of ADCB for differentiating MMN from ALS, the authors recorded the compound muscle action potentials (CMAPs) from small hand muscles by magnetically stimulating nerve roots before and after 1 minute of maximal voluntary contraction (magnetic fatigue test). They examined nine patients with MMN with unequivocal clinical responses to IV immunoglobulins (IVIgs), yet lacked CB according to the conventional criteria.
Six MMN patients had postexercise CB/temporal dispersion maximum in the immediate postexercise period. ADCB in an MMN patient improved after IVIg. Further analysis revealed that prolongation of the duration from the onset to the positive peak of the CMAP was the most sensitive indicator for MMN, presumably because the phase cancellation obscures the abnormalities of the other parameters.
The magnetic fatigue test is useful in detecting mild conduction block presumably located in a proximal nerve segment in patients with multifocal motor neuropathy who do not fulfill its conventional electrodiagnostic criteria.
Neurology 08/2006; 67(2):280-7. · 8.31 Impact Factor
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T Oga,
M Honda,
K Toma, N Murase,
T Okada,
T Hanakawa,
N Sawamoto,
T Nagamine,
J Konishi,
H Fukuyama,
R Kaji,
H Shibasaki
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ABSTRACT: Although it is hypothesized that there is abnormal motor inhibition in patients with dystonia, the question remains as to whether the mechanism related to motor inhibition is specifically impaired. The objective of the present study was to clarify the possible abnormalities of the mechanisms underlying voluntary muscle relaxation during motor preparation and execution in patients with writer's cramp, using event-related functional MRI. Eight patients with writer's cramp and 12 age-matched control subjects participated in the study. Two motor tasks were employed as an experimental paradigm. In the relaxation task, subjects were asked to hold their right wrist in the horizontal plane by maintaining moderate contraction of wrist extensor muscles in the premotor phase; they relaxed those muscles voluntarily just once during each fMRI scanning session. In the contraction task, subjects extended the right wrist voluntarily from the same premotor state as for the relaxation task. Five axial images covering the primary sensorimotor cortex (SMC) and supplementary motor area (SMA) were obtained once every second. Activated volumes in the left SMC and the SMA were significantly reduced in patients for both muscle relaxation and contraction tasks. These data suggest that there is impaired activation in both SMC and SMA in voluntary muscle relaxation and contraction in patients with writer's cramp. This implies that abnormalities of both inhibitory and excitatory mechanisms in motor cortices might play a role in the pathophysiology of focal dystonia.
Brain 05/2002; 125(Pt 4):895-903. · 9.46 Impact Factor
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ABSTRACT: In order to explore the pathophysiology of diabetic neuropathy, we studied serial changes of axonal excitability in 20 adult Wistar rats with streptozocin-induced diabetes using the technique of threshold electrotonus (TE). After persistent hyperglycaemia had developed, rats were divided into two groups: nine were fed a diet containing aldose reductase inhibitor (Epalrestat 30 mg/kg/day) (ARI(+) group) and 11 were fed a diet without the inhibitor (ARI(-) group). Eight normal control rats of similar age (NC group) were also studied. We monitored membrane properties of motor axons in the tail for 3 months using TE to measure the changes in excitability induced by subthreshold polarizing currents while recording compound muscle action potentials (CMAPs) in the tail muscle. The ARI(-) group showed a significant increase in CMAP latency 1 month after streptozocin injection, and by 3 months there was significantly lower excitability after hyperpolarization for 100 ms compared with the NC group. A similar change in TE was reproduced by injection of caesium chloride, an inhibitor of inward rectification. By contrast, the ARI(+) group exhibited no significant change in TE or latency at 3 months, although they showed significant body weight loss and hyperglycaemia. These findings indicate that inward rectification is reduced in an experimental model, as in human diabetes, and that blocking the polyol pathway with an ARI prevents this reduction. Reduced inward rectification potentiates conduction block caused by activity-dependent hyperpolarization and may underlie the decreased vibratory sensation seen in the early stage of diabetic neuropathy.
Brain 07/2001; 124(Pt 6):1149-55. · 9.46 Impact Factor
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ABSTRACT: A GAG deletion at position 946 in the DYT1 gene has been identified as one of the gene mutations responsible for autosomal dominant primary torsion dystonia. We examined 178 Japanese patients with various forms of dystonia, and found the mutation in six patients (3.4%) from three families. Five of them had early clinical onset (before age 12) with initial involvement of a limb. To our knowledge, this is the first report of the frequency and the clinical features of DYT1 mutation in oriental patients, and the clinical presentation of the mutation in these patients was similar to that of Jewish or non-Jewish Caucasian patients.
Neuroreport 04/2001; 12(4):793-5. · 1.66 Impact Factor
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Movement Disorders 12/2000; 15(6):1276-9. · 4.51 Impact Factor
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ABSTRACT: One characteristic of focal dystonia is the sensory trick, by which sensory input to a certain area of the body can reduce abnormal contractions in muscles nearby. This suggests that adjusting the link between sensory input and movement allows motor commands to be issued more effectively from the brain. To explore this sensorimotor link, we studied the attenuation (gating) of somatosensory evoked potentials (SEPs) before and during hand movements in patients with writer's cramp. For premovement gating, 10 patients and 11 age-matched normal subjects were given a warning sound followed 1s later by an electric stimulus to the right median nerve at the wrist. The latter served both as a reaction signal to start a finger extension task and as the input to evoke SEPs over the scalp. Because reaction times always exceeded 70 ms, short-latency SEPs thus obtained were unaffected by the afferents activated by the movement. The amplitudes of frontal N30 components were significantly decreased over the frontal leads compared with SEPs elicited at rest (P: < 0.002) in the normal group, whereas significant gating was found not for N30 but for frontal P22 (P: = 0. 002) in the patient group. For midmovement gating studies, SEPs to the right median nerve stimulation were recorded in 16 patients and 12 age-matched normal subjects at rest, and during active and passive finger extension-flexion movements. In contrast to the premovement SEPs, the frontal N30 was equally gated during active and passive movements both in the patient (P: < or = 0.002) and the normal group (P: < or = 0.003). These findings indicate that in writer's cramp the sensitivity of sensory input channels from the hand is wrongly set by the central command to move. Perhaps the sensory trick, by supplying additional input not usually present during unobstructed movement, is a manoeuvre to correct this imbalance. Dystonia may result not only from abnormalities in the central motor command but also from disturbed central processing of sensory input.
Brain 10/2000; 123 ( Pt 9):1813-29. · 9.46 Impact Factor
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ABSTRACT: Patients with multifocal motor neuropathy may complain of muscle fatigue, even though the degree of conduction block assessed at rest has improved with treatment. To explore the mechanism involved, we examined changes in muscle force during maximum voluntary contraction (MVC) and monitored conduction block before and after MVC in five patients with multifocal motor neuropathy. The results were compared with those for the contralateral unaffected homonymous muscles. For one patient, who had bilateral involvement, a normal subject of a similar age and stature served as the control. Results of conduction studies were also compared with those from six patients with amyotrophic lateral sclerosis (ALS) with similar compound muscle action potential (CMAP) amplitudes after proximal stimulation. During MVC for 60 s, the affected muscles developed prominent fatigue; the force at the end of contraction compared with the initial force was significantly lower for the affected muscles [42 +/- 19% (mean +/- standard deviation) of the initial force] than for the control muscles (94 +/- 9%; P = 0.01). After MVC, the amplitude ratio of CMAPs after proximal versus distal nerve stimulation transiently decreased to 19 +/- 14% of that before MVC in the affected muscles, but not in the control muscles (94 +/- 3.8% of that before MVC) and in patients with ALS (95 +/- 6.7%). In one patient with a focal lesion in the forearm, nerve excitability was monitored at the lesion site before and after MVC for 120 s. There were significant increases in axonal threshold (approximately 48%) and supernormality (approximately 135%) immediately after MVC, suggesting that the axonal membrane had undergone hyperpolarization and, by extrapolation, that this had precipitated the conduction block. This study is the first to show that activity-dependent conduction block plays a role in human disease by causing muscle fatigue.
Brain 09/2000; 123 ( Pt 8):1602-11. · 9.46 Impact Factor
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ABSTRACT: Somatosensory evoked potentials (SEPs) are reduced in amplitude during movement (gating). The mechanism involves central gating of afferent input and competition from other afferents activated by the movement. We distinguished these two by giving 11 normal subjects a warning sound followed 1 s later by an electric stimulus to the right median nerve at the wrist. The latter served both as a cue to start a finger movement and as stimulation to evoke SEPs. Gating effects were widespread in frontal (N30) and central (N60) areas, but were also seen, albeit to a lesser extent, in the recordings at P3 (P30). Since finger movement began after the stimulus, such gating must have been purely central in origin, presumably reflecting motor preparation.
Neuroreport 09/1999; 10(12):2457-60. · 1.66 Impact Factor
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ABSTRACT: Spasticity is partly caused by disinhibition of spinal stretch reflex activity and blocking of the group Ia afferents may improve its clinical symptoms. Since muscle afferent block has been successfully used for treating dystonia, this method may become useful for treating spasticity as well. We injected diluted lidocaine (0.5%, 50 ml/session) and ethanol (5 ml) into thigh adductors (for leg crossing), medial hamstrings (for medial rotation of the leg), quadriceps femoris (for hyperextension of the knee), tibialis posterior and triceps surae muscles (pes equinovarus deformity), biceps brachii and forearm flexors (for flexion deformities of the upper extremity) in 12 patients with spasticity. Although the duration of action was short (< 1 day) at first, it was gradually prolonged to several weeks by repeating the injection every 3-4 days. The final outcome was comparable to that obtained by botulinum toxin injection in the same group of patients. This method may prove its promise as a means of treating spasticity.
Rinsho shinkeigaku = Clinical neurology 12/1996; 36(12):1334-5.
