A 25-Year-Old Man With Painless Diplopia

Sumaira Nabi, MBBS, FCPS; Shahzad Ahmed, MBBS; Fateen Rashid, MBBS; Mazhar Badshah, MBBS, FCPS

Disclosures

August 09, 2016

INO can be unilateral or bilateral. The most common cause of unilateral INO in elderly persons is stroke. In young patients with unilateral or more typically bilateral INO, multiple sclerosis (MS) is the most frequently implicated underlying cause, with a reported incidence of 34% in one study.[7] INO is clinically elicited in 15%-38% of patients with MS.[8,9] The location of the MLF in the periventricular area is assumed to make it prone to the inflammatory demyelination of MS. Other unusual etiologies include head trauma; tumors; infective lesions (eg, tuberculomas); hydrocephalus; Arnold-Chiari malformation; transtentorial herniation; brain hemorrhage; venous infarction; subdural hematoma; and vasculitis, such as that due to systemic lupus erythematosus.[7,10,11]

Lhermitte[12] was the first to have used the term "ophthalmoplegia internuclearis" in 1922. Further research into the neuroophthalmology of MS revealed other closely related syndromes, including wall-eyed monocular INO (WEMINO), wall-eyed bilateral INO (WEBINO), and one-and-a-half syndrome.[1]

WEMINO is characterized by INO that is associated with exotropia on the same side. This syndrome also results from injury to the MLF but is less frequently encountered.[13] WEBINO is also a rare variant of INO that consists of adduction deficits on both sides, with bilateral exotropia in the primary position of gaze due to disruption of convergence pathways. The proposed etiology is a midbrain lesion involving bilateral medial rectus subnuclei and MLF. However, some consider it a pontine rather than a midbrain syndrome.[14]

One-and-a-half syndrome is the result of injury to the PPRF and/or abducens nucleus and the ipsilateral MLF. Upon ocular motility testing, the vertical eye movements remain intact, whereas on attempted horizontal gaze, only abduction of the contralateral eye is possible. In other words, it consists of conjugate horizontal gaze palsy in one direction with an INO in the other direction. Several causes are noted, with MS implicated in 9.1% cases.[1]

INO is typically diagnosed on the basis of neurologic examination findings, with weakness of adduction in the affected eye and nystagmus of the contralateral abducting eye. Milder cases with subtle findings can be often missed on clinical examination. These findings can be discovered using specialized techniques, such as optokinetic tape and oculographic recordings.[15,16] Brain MRI with contrast must be performed in all patients presenting with INO. Stroke and tumor are easily demonstrated. In cases of MS, only 57.1% patients have characteristic lesions on MRI.[1] Proton density imaging is thought to be more sensitive in detecting lesions.

Another closely related entity that should be considered during examination is pseudo-INO, which is seen in patients with myasthenia gravis and Guillain-Barré syndrome.[17,18]

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