Isolated Horizontal Gaze Palsy: Observations and Explanations

Abstract

We present three cases that we suggest require a novel diagnosis and a reconsideration of current understandings of pontine anatomy. In this case series, we highlight a series of patients with monophasic, fully recovering inflammatory lesions in the pontine tegmentum not due to any of the currently recognized causes of this syndrome. We highlight other similar cases in the literature and suggest there may be a particular epitope for an as-yet-undiscovered antibody underlying the tropism for this area. We highlight the potential harm of misdiagnosis with relapsing inflammatory or other serious diagnoses with significant adverse impact on the patient. In addition, we propose that this would support a reinterpretation of the currently accepted anatomy of the pontine gaze inputs to the median longitudinal fasciculus and paramedian pontine reticular formation.

Keywords: horizontal gaze; median longitudinal fasciculus; ophthalmoplegia; paramedian pontine reticular formation; pontine anatomy.

Figure 1

(A) I. Patient 1, axial fluid-attenuated inversion recovery (FLAIR) showing hyperintense lesion in posterior pontine tegmentum. II. Saggital FLAIR showing vertical extent of the lesion. III. Diffusion-weighted imaging showing mild diffusion restriction. (B) I. Patient 2, axial dual showing hyperintense lesion in posterior pontine tegmentum. II. Saggital FLAIR showing vertical extent of the lesion. III. Diffusion-weighted imaging showing mild diffusion restriction. (C) I. Patient 3, axial flair showing hyperintense lesion in posterior pontine tegmentum, slightly more significant on the right side. II. Saggital FLAIR showing vertical extent of the lesion, slightly larger than the previous two patients, consistent with there being some slowing of vertical saccades. III. Diffusion-weighted imaging showing mild diffusion restriction.

Figure 2

(A) A section through the mid-pons showing the relationship of the paramedian pontine reticular formation to the median longitudinal fasciculus (MLF) and the adjacent seventh cranial nerve as it sweeps around the abducens nucleus. (B) A magnification showing the proposed conformation of the separate horizontal and vertical gaze paths as they project into the MLF. The horizontal signal decussates at the level of the pons and ascends in the contralateral MLF while it is uncertain whether the vertical gaze signal decussates at all, or is a direct projection.