Distinguishing Internuclear Ophthalmoplegia from 6th Nerve Palsy

Clinical Examination Findings

The American Academy of Ophthalmology notes that 6th nerve palsy produces an abduction deficit of the affected eye, which cannot move laterally past midline, and incomitant esotropia that increases when looking toward the side of the paretic lateral rectus muscle, with a compensatory head turn toward the side of the palsy to maintain fusion 1, 2, 3
The American Academy of Ophthalmology recommends that convergence testing be used to distinguish INO from 6th nerve palsy, as convergence is normal in 6th nerve palsy, with both eyes adducting normally 1, 2

The American Academy of Neurology suggests that other cranial neuropathies, such as 3rd or 4th nerve involvement, in patients with 6th nerve palsy, may indicate cavernous sinus or brainstem pathology, and that papilledema may suggest elevated intracranial pressure 1, 3
The American Academy of Neurology notes that bilateral 6th nerve palsy may suggest increased ICP, meningeal process, or clival chordoma 1

The American College of Radiology recommends that neuroimaging, such as MRI brain with contrast, be indicated for young patients with 6th nerve palsy, those without vasculopathic risk factors, bilateral involvement, other cranial neuropathies, or signs of elevated ICP 1, 2, 3