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Unilateral INO is associated with ocular tilt reaction in pontomesencephalic lesions

INO plus

From the Departments of Neurology (A.Z., C.C., V.A., M.G., T.B., M.S.) and Neuroradiology (G.F.), Ludwig-Maximilians-University, Klinikum Grosshadern, Munich, Germany.

Address correspondence and reprint requests to Dr. Andreas Zwergal, Department of Neurology, University of Munich, Klinikum Grosshadern, Marchioninistrasse 15, D-81377 Munich, Germany andreas.zwergal{at}med.uni-muenchen.de

Objective: Correlation of internuclear ophthalmoplegia (INO) with components of the ocular tilt reaction (OTR) in order to localize graviceptive (specifically otolithic) pathways in the brainstem.

Methods: We retrospectively analyzed data of 120 patients with INO (87 unilateral [9 of whom had one-and-a-half syndrome], 33 bilateral) for OTR (subjective visual vertical [SVV], ocular torsion, skew deviation) to localize causative brainstem lesions in MRI.

Results: Unilateral INO was accompanied by at least one component of OTR: SVV tilt in 96%, ocular torsion in 79%, and skew deviation in 50%. All components were directed to the contralesional side. Contralateral OTR occurred in 89% of patients with one-and-a-half syndrome. Only 9% of patients with bilateral INO exhibited OTR. MRI showed distinct lesions in 68%, which almost exclusively projected onto the pontomesencephalic medial longitudinal fascicle (96%). Follow-up measurements revealed SVV and ocular torsion normalized faster than the adduction deficit in INO.

Conclusions: First, unilateral internuclear ophthalmoplegia (INO) is regularly associated with contraversive ocular tilt reaction (OTR): INO plus. Thus, graviceptive pathways join the medial longitudinal fascicle after crossing between the vestibular and abducens nuclei. Second, the different time course and degree of recovery of OTR components and INO signs can be explained by the hypothesis that vestibular tone imbalance is compensated by central vestibular adaptation mechanisms (probably driven mainly by cerebellar-vestibular projections), whereas impaired adduction is less susceptible to compensation according to Hering’s law and can only be overcome by lesion repair. Third, bilateral INO is seldom associated with OTR, confirming that bilateral impairment of graviceptive pathways does not cause imbalance in roll plane.

Abbreviations: INC = interstitial nucleus of Cajal; INO = internuclear ophthalmoplegia; MLF = medial longitudinal fascicle; MS = multiple sclerosis; OTR = ocular tilt reaction; SVV = subjective visual vertical.

Supplemental data at www.neurology.org

Supported by Biogen Idec.

Disclosure: The authors report no disclosures.

Received September 28, 2007. Accepted in final form May 19, 2008.

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