Pure Isolated Internuclear Ophthalmoplegia As A Presentation Of Midbrain Ischemic Stroke: A Case Report

Abstract

Background:

Internuclear ophthalmoplegia (INO) is a disorder of conjugate eye movements caused by lesions of the medial longitudinal fasciculus (MLF). Demyelination remains the most common etiology, while ischemic causes are less frequently observed. Isolated midbrain infarction presenting exclusively as INO is particularly rare.

Case Presentation:

A 48-year-old man presented with sudden onset dizziness and unsteady gait. Neurological examination revealed impaired adduction of the right eye with abducting nystagmus of the contralateral eye during left gaze, consistent with right-sided internuclear ophthalmoplegia. Other cranial nerve functions were intact, and systemic examination was unremarkable. Magnetic resonance imaging of the brain demonstrated a small focal acute infarct in the left lower anterior midbrain.

Discussion:

Most vascular INO lesions are localized to the pontine region; isolated involvement of the midbrain is infrequently reported. The paramedian location of the MLF at the midbrain level explains how small focal infarcts can produce isolated ocular findings without accompanying neurological deficits.

Conclusion:

Isolated internuclear ophthalmoplegia may be the sole manifestation of midbrain ischemic stroke. Careful ocular motor examination and early neuroimaging are critical for accurate diagnosis of subtle posterior circulation strokes.