下眼瞼向き眼振を呈した17症例の臨床的検討

Clinical analysis of 17 cases with down beat nystagmus

はじめに

　下眼瞼向き眼振（DBN：down beat nystagmus）は約40％が特発性で原因不明とされている^1）。DBNが前庭小脳の障害によって認められるとの報告は多く，局在診断的意義も大きいとされている。脊髄小脳変性症（SCD：spinocerebellar degeneration）とDBNとの関係については，同眼振を認める50症例の検討を行ったところ38症例が中枢性であり，そのうち，13症例の非遺伝性多系統萎縮症（MSA：multiple system atrophy）型のSCDを含んでいたとの報告がある^2）。またSCDのうち脊髄小脳変性症6型（SCA6：spinocerebellar ataxia type 6）においては84％の症例に頭位変換時のDBNを認めたのに対してMSA症例では6.3％にとどまり，DBNはSCA6に有意に多いと報告されている^3）。SCDによる小脳機能不全症状がしばしば末梢性めまいと類似するため，約25％の患者が耳鼻咽喉科を受診すると報告されている^4）。このためSCDを適切に診断し，治療および社会支援に向けての耳鼻咽喉科医の責務は大きなものと考える。そこで，当院を受診したDBNを認めた17症例についての検討を行った。

　The down beat nystagmus was found in 17 cases among the cases that performed the first medical examination in our clinic for dizziness or vertigo from August, 2008 to April, 2015. It has been said that approximately 40％ are idiopathic, and the nystagmus is unidentified, but a vestibulocerebellum disorder often causes it, and the disinhibition of the ascending neuron of the superior vestibular nucleus by the obstacle of the part is done with onset mechanism. We performed clinical examination in the cases with nystagmus in our clinic. The sex was 11 men, 6 women. The drift at the time of the walk was strong and the patients were consulted for neurology about the case that presented an unbalance-related pattern by examination of eye-tracking test, spinocerebellar degeneration（SCD）was diagnosed in three cases by MRI and neurologic examinations. As for the breakdown, cortical cerebellar atrophy（CCD）, spinocerebellar ataxia type 6（SCA6）by genetic screening, multiple system atrophy（MSA）were found in each case. The other four cases that shifted to two cases that were posterior semicircular canal type benign paroxysmal positional vertigo（BPPV）, while horizontally（the outside）semicircular canal type BPPV was seenin two cases. In addition, we recognized two cases of Meniere's disease from hearing ability image and a clinical course. It was unidentified in other eight cases. It was judged to be effective about the inspection of the neuro-otological examination by the otolaryngologist on SCD. In recent treatment with medical therapy, rehabilitation progressed, and, as for the SCD, it was thought that the role of the otolaryngologist who was available for early detection was important.