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Multiple sclerosis (MS) can present to the ophthalmologist with visual loss (e.g., opticneuritis), diplopia (e.g., internuclear ophthalmoplegia [INO] or sixth-nerve palsy), or nystagmus.
Some localizing and non-localizing forms of nystagmus seen in MS are listed in Table 1. An INO is characterized by an ipsilateral adduction deficit and a contralateral abducting dissociated horizontal nystagmus on horizontal gaze. In a young patient, a new INO should be considered to represent MS until proven otherwise. The lesion involves the medial longitudinal fasciculus (MLF), the interneuron between the sixth- and third-nerve nuclei. Careful attention to the horizontal saccades might bring out a subtle INO. Table 2 lists some common features of the INO.
Jerk beating nystagmus is named for the fast phase (e.g., fast phase down = beating nystagmus). Downbeat nystagmus typically worsens in downgaze and lateral gaze and localizes to the cervicomedullary junction. Upbeat nystagmus localizes to the pontomedullary junction or in some cases the cerebellar vermis. Periodic alternating nystagmus (PAN) demonstrates a horizontal fast phase in one direction, followed by a slowing of the nystagmus, a null phase with minimal or no eye movement, and then the nystagmus alternates with the fast phase toward the opposite direction. Acquired pendular nystagmus has an equal amplitude and frequency in both directions and is a relatively common finding in MS.
Summary Ophthalmologists should be aware that nystagmus can be the presenting or only sign of MS. The abducting nystagmus of the INO and acquired pendular nystagmus are common nystagmus presentations. Cranial MRI with contrast enhancement is the procedure of choice for evaluating nystagmus. Optical, medical, and surgical treatments might help selected patients.
G. Lee, MD, is editor of The Neuro-Connection. He is a professor of ophthalmology, neurology, and neurosurgery at the University of Iowa Hospitals and Clinics, Iowa City.
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