Ｓｕｐｅｒｉｏｒ ｏｂｌｉｑｕｅ ｍｙｏｋｙｍｉａの発生機序について

Abstract

Superior oblique myokymia is an intermittent uniocular microtremor caused by uncontrolled contractions of the superior oblique muscle, termed by Hoyt and Keane. As all the previously reported cases were healthy individuals, its lesion and mechanism have not been clarified. In this report, I introduced a patient with a cerebellar tumor who presented with superior oblique myokymia.A 41-year-old woman was admitted to the Nihon University Hospital with complaints of headache, dizziness and diplopia. A right cerebellar cyst was observed on computerized tomography and partial resection of this tumor was performed. Two months after this operation, she complained of oscillopsia and torsional diplopia. At that time, rapid, smallamplitude, intorted movements, that is superior oblique myokymia, were noted only in the right eye. This abnormal eye movement disappeared in one week. Thereafter, left cerebellar signs became apparent and visual suppression of nystagmus was reduced on both sides. Therefore, it was suspected that the tumor had already extended to the left cerebellum.From this clinical course and the experimental data of Ito, it was suggested that when the left flocculus was stimulated, the left superior vestibular nucleus was inhibited. Disinhibition of the right superior oblique muscle and disfacilitation of the right inferior oblique muscle resulted and the intorted movement appeared in the right eye.From these results, it seemed that the lesion responsible for superior oblique myokymia was the contralateral flocculus and this characteristic eye movement was produced when this region was stimulated temporarily.