2019 年 78 巻 4 号 p. 256-266
Ocular tilt reaction (OTR) is the roll-plane manifestation of a vestibular tone imbalance, characterized by ocular torsion, skew deviation, and tilts of the subjective visual vertical (SVV) with/without head tilts. The OTR can result from any unilateral lesion of the graviceptive pathways from the labyrinth to the contralateral interstitial nucleus of Cajal in the rostral midbrain via the medial longitudinal fasciculus. All tilt effects are ipsiversive, with a unilateral lesion below the crossing of the graviceptive pathways. All tilt effects are contraversive, with a unilateral pontomesencephalic lesion. The OTR may only induce vertical diplopia subjectively. While vertical diplopia from the OTR is well-known in brainstem lesions, the peripheral OTR is rare and fleeting and usually seen after acute vestibular deafferentation. By contrast, the OTR in our case with a vestibular schwannoma suggests a chronic peripheral form. Despite complete left canal paresis in our case, dizziness or imbalance had become unrecognizable, masked by central vestibular compensation. Consistently, along with the tumor growth, the patient's OTR improved, possibly through central adaptation promoted by further utricular damage in the vestibulocochlear nerve. Through a literature survey, we wish to make at least three statements regarding the peripheral OTR: 1) overt OTR is infrequent or may have escaped recognition in the acute phase of vestibulopathy because of vertigo/nystagmus and neurovegitative symptoms; 2) the causal relationship between ocular torsion and SVV tilts has yet to be resolved, and 3) ocular torsion may be conjugate or disconjugate with the larger extorsion of the ipsilateral eye.