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Iowa City-Multiple sclerosis (MS) is associated with the development of various forms of nystagmus. The association is so strong that new-onset nystagmus in an adult should be considered MS until proven otherwise.
Andrew G. Lee, MD, professor of ophthalmology, neurosurgery, and neurology, H. Stanley Thompson Neuro-ophthalmology Clinic at the University of Iowa Hospitals and Clinics, Iowa City, described how to recognize the common forms of nystagmus associated with MS and where the brain lesions are likely located.
"The most common form of nystagmus in MS is internuclear ophthalmoplegia, an adduction deficit and a dissociated abducting eye nystagmus that occurs in horizontal gaze in the direction away from the lesion in the medial longitudinal fasciculus (MLF)," Dr. Lee explained.
Locating the lesion
"It is important to recognize these forms of nystagmus because they have localizing value, that is, they tell you where the lesion is," he emphasized.
An internuclear ophthalmoplegia localizes to the MLF on the side of the adduction deficit. An acquired pendular nystagmus can originate from the cerebellum or brainstem. Upbeating nystagmus originates at the level of the vermis or brainstem, downbeating nystagmus at the level of the cervical medullary junction, and periodic alternating nystagmus in the cerebellum. The presence of internuclear ophthalmoplegia, especially if bilateral, strongly indicates MS in a young individual.
"A new-onset internuclear ophthalmoplegia in a young person represents MS until proven otherwise. If the patient is older, the diagnosis is likely an ischemic brainstem event," Dr. Lee said. "New-onset acquired pendular nystagmus in an adult is MS, until proven otherwise."
Upbeating nystagmus with the fast phase up is present in primary position. This nystagmus tends to be worse in upgaze, and is localized to the vermis, but the lesion can also be in the brainstem, including the posterior fossa, but especially in the medulla, according to Dr. Lee.
"The ascending pathways from the anterior semicircular canals at the junction of the pons and the medulla or at the junction of the midbrain and the pons can produce upbeating nystagmus," he said.
Downbeating nystagmus localizes to the cervical medullary junction, the junction between the cervical cord and the medulla. This nystagmus is present in primary position when it is pathologic; it is worse in lateral and down-gaze.
"At the level of the cervical medullary junction, even though a common structural cause of downbeating nystagmus is the Arnold-Chiari malformation, a very common pathologic cause is demyelinating disease in adults. Downbeating nystagmus is a central form of vestibular nystagmus," he said.
The localizing value of the nystagmus is lost if there is just downbeating or upbeating in the respective direction but not while in primary gaze. The presence of downbeating nystagmus or upbeating nystagmus in primary gaze educates the clinician to the location of the lesion.
Dr. Lee offered a warning about correctly identifying periodic alternating nystagmus. In a patient who seems to have a horizontal nystagmus that is beating to the right, for example, the individual should be observed for at least 1 minute to determine if the nystagmus is alternating.
"Every patient with horizontal nystagmus should be observed for a couple of minutes to differentiate it from periodic alternating nystagmus because, unlike many of the nystagmus treatments that do not work well, baclofen (Lioresal Intrathecal, Medtronic) seems to work better for periodic alternating nystagmus. It is important to make the diagnosis because this is one of the few treatable forms of nystagmus," he advised.