Acquired Binocular Pendular Nystagmus

What is it?

Pendular nystagmus associated with a brainstem or diencephalic lesion
Common causes: multiple sclerosis, brainstem/cerebellar tumor, stroke, hemorrhage, inflammation
Uncommon causes: neurodegenerative states, Pelizaeus-Merzbacher disease, Whipple disease, chiasmal or thalamo-mesencephalic lesion, albinism

Core clinical features
- Patient often reports blurred vision or that objects appear to be oscillating (“oscillopsia”)
- Pendular nystagmus of both eyes with a purely torsional trajectory or a mixed horizontal/vertical/torsional trajectory
- Eyes appear to oscillate in a elliptical or circular trajectory (“multivector nystagmus,” “egg beater nystagmus”)
- Oscillation amplitude is often greater in one eye than in the other eye
Possible accompanying clinical features
- Ataxia
- Skew deviation
- Saccadic pursuit
- Extremity weakness
In a variant called Seesaw Nystagmus, one eye moves upward and intorts while the other eye moves downward and extorts
In a variant called Oculopalatal Tremor, the eyes move in synchrony with pendular oscillations of the palate, platysma, pharynx, larynx, or diaphragm
In a variant called Oculomasticatory Myorhythmia, the eyes converge synchronously with masticator muscle spasms, usually a sign of Whipple disease

If you detect a seesaw trajectory, look for a diencephalic (including chiasmal) lesion and albinism

If you see synchronous palatal movements, look for high T2/FLAIR signal in the inferior olivary nucleus on MRI,

which is a central nervous system adaptation to a chronic brainstem lesion
If you see convergence oscillations and associated jaw muscle tightening, try to say “oculomasticatory myorhythmia” and evaluate the patient for Whipple disease

Nystagmus may lessen or disappear if the underlying lesion is successfully treated
Gabapentin or memantine may improve oscillopsia, but side effects are common
Seesaw nystagmus variant may be helped by baclofen, clonazepam
Trap: intramuscular and retrobulbar botulinum toxin injections do not reduce oscillopsia or improve vision
Trap: large extraocular muscle recessions do not reduce oscillopsia or improve vision