体性感覚誘発電位と長潜時反射の関連について—基礎的検討と多発性硬化症への応用

CORRELATION BETWEEN SOMATOSENSORY EVOKED POTENTIALS AND LONG LOOP REFLEXES: BASIC INVESTIGATION AND ITS APPLICATION FOR MULTIPLE SCLEROSIS

　抄録　正常群25名，多発性硬化症（MS）症例25例から体性感覚誘発電位（SEP）と長潜時反射（LLR）を記録した。正常群では母指球筋の等張性収縮により得られた筋電図をトリガーとして正中神経に刺激を加える方法により，上肢のLLRは100％出現した。その出現閾値はH波より低く，平均潜時は40.0±1.5msで，身長と強い正の相関を示し，SEPのN20とも強い正の相関を認めた。正常群15名からは下肢のLLRも記録したが，下肢のH波とLLR間潜時は上肢に比し有意に長かった。正中神経刺激部位を手首から肘部に移動すると，M波とH波間潜時は短縮し，筋の持つ固有振動数に応じて各波が出現するとした反響仮説は否定的と考えられた。MS群では，LLRは64％で異常を示した。N20とLLRの潜時の関係から全体を4群，すなわち，N20,LLR共に正常の群，N20もLLRも延長しているが，両者が正常群と同じ関係を保っている群，N20は正常だが，LLRは延長している群，N20,LLRは共に延長しているが，LLRの延長がN20の延長から予想される以上に著明な群に分類し解析を試み，LLRが長ループ反射である可能性と，その臨床応用の有用性について考察した。

Somatosensory evoked potentials (SEPs) and long loop reflexes (LLRs) to the median nerve stimu-lation were investigated on 25 normal controls and 25 patients with multiple sclerosis (MS). Fifteen normal controls were also subjected to LLR study by the common peroneal nerve stimu-lation. The mean height were 159±8. 2 cm in nor-mal controls and 160±8. 9 cm in MS, respectively.

LLRs were obtained with 100% reproducibility in all cases. Upper limb LLRs were recorded from m. abductor pollicis brevis by trigger stimulation during isotonic contraction of the thumb, while lower limb LLRs were recorded from m. peroneus longus by trigger stimulation during isotonic ever-sion of the foot. The threshold of LLR was lower than that of short latency reflex (H-wave) with the mean latency of 40. 4±1. 5 ms. The height of subjects revealed an obvious positive correlation not only with the latency of LLR but also with N 20 of SEP, whereas central conduction time was not. Furthermore, a significant correlation was present between the latencies of LLR and N 20, showing a twofold gradient of LLR against N 20. There was a significantly prolonged latency diffe-rence between H-wave and LLR of lower limb as compared with that of upper limb. When the sti-mulation site was changed from the wrist to the elbow, the latency difference between M-wave and H-wave shortened. This fact, therefore, ap-pears to be against "resonance hypothesis" thatLLR is set off according to the intrinsic mecha-nical osscilation given to the muscle concerned.

In MS as a whole LLR was abnormal in 60%, but the incidence of LLR abnormality was 33% in possible MS, 64% in probable MS and 88% in clinically definite MS in the increasing order of certainity.

Finally we proposed to set up 4 groups from the relationship of latencies between N 20 and LLR, namely, A ; both N 20 and LLR are normal, B ; both N 20 and LLR are abnormally prolonged with the same ratio as seen in A, C ; N 20 is nor-mal, while LLR is abnormally prolonged, D ; both N 20 and LLR are abnormally prolonged, yet LLR prolongation is greater than expected from N 20 prolongation. The practical interpretation of the above 4 groups are as follows. A ; both the pos-terior column and the pyramidal tract are intact, B ; main disturbance is in the posterior column with the pyramidal tract spared, C ; main distur-bance is in the pyramidal tract with the posterior column spared, D ; both the posterior column and the pyramidal tract are involved. Applying the above method to MS patients, this classification turn out good enough to reflect the neurological status.