Bilateral Internuclear Ophthalmoplegia Caused by Minor Head Injury: A Case Report

Bilateral internuclear ophthalmoplegia (INO) is rare, with vascular disease and multiple sclerosis being the most common causes. We report an unusual case of isolated bilateral INO following minor brain injury. A 61-year-old Asian woman developed binocular diplopia after a minor motorbike accident. Neurological examination revealed bilateral INO with impaired adduction in both eyes and abducting nystagmus in the contralateral eye. Initial brain computed tomography was unremarkable, but brain magnetic resonance imaging (MRI) 2 days later revealed a subtle paramedian pontomesencephalic hyperintensity on T2-weighted imaging, which became more pronounced with contrast enhancement, suggesting the axonal injury secondary to trauma. Minor head trauma can cause bilateral INO due to subtle brainstem injury, even without other deficits. Shear forces may lead to vascular and axonal damage in the medial longitudinal fasciculus. MRI with contrast is essential for detection. Although rare, isolated bilateral INO should be considered posthead trauma.