Multiple Sclerosis is the Most Likely Cause
Multiple sclerosis is definitively the most likely cause of jerking eye movements (nystagmus) on lateral gaze in this patient, given that gaze-evoked nystagmus is one of the most frequent chronic ocular motor manifestations of MS and occurs in approximately 13.5% of MS patients. 1, 2
Clinical Reasoning
Why Multiple Sclerosis is the Answer
Gaze-evoked nystagmus (GEN) is a central form of nystagmus that definitively indicates pathology in the brainstem or cerebellum, which are heavily myelinated regions characteristically affected by MS demyelinating lesions 3, 4
MS patients demonstrate ocular motor disorders in 68.1% of cases, with gaze-evoked nystagmus being among the most common chronic manifestations alongside internuclear ophthalmoplegia and saccadic dysmetria 2
The jerking movement on lateral gaze described in this patient is consistent with GEN, which is a cerebellar ocular motor disorder that does not fatigue and is not suppressed by visual fixation—hallmarks of central pathology 3, 1
MS lesions within the brainstem and cerebellum frequently result in ocular motor disorders, particularly affecting the vestibulocerebellum and producing abnormalities of gaze and nystagmus 4
Why the Other Conditions Are Less Likely
Myasthenia Gravis:
- While myasthenia gravis can cause diplopia and ocular muscle weakness, it characteristically produces fatigable weakness that worsens with sustained gaze, not the persistent jerking nystagmus described 1
- Nystagmus is not a typical feature of myasthenia gravis
Graves' Disease:
- Thyroid eye disease causes restrictive esotropia and limitation of ocular rotations due to extraocular muscle enlargement and fibrosis 5
- It does not produce gaze-evoked nystagmus as a characteristic finding
Cluster Headaches:
- Cluster headaches are a pain syndrome without associated ocular motor abnormalities
- They do not cause nystagmus or jerking eye movements
Neurofibromatosis:
- While neurofibromatosis can cause optic pathway gliomas and other CNS tumors, it does not characteristically produce gaze-evoked nystagmus
- Tumors causing nystagmus would more likely produce other focal neurological signs
Key Distinguishing Features
The pattern of nystagmus matters: The American Academy of Otolaryngology-Head and Neck Surgery identifies gaze-evoked nystagmus as a central finding that helps distinguish central from peripheral causes of vertigo and ocular motor dysfunction 3
MS has the highest association with this specific finding: Among the conditions listed, only MS characteristically produces gaze-evoked nystagmus as a direct consequence of demyelinating plaques in the brainstem and cerebellum 1, 2, 4
Clinical Implications
This patient should already have MRI documentation of MS lesions given her established diagnosis, and the presence of infratentorial lesions would correlate with the ocular motor findings 2
The finding of gaze-evoked nystagmus in this MS patient indicates subclinical disease activity in the posterior fossa structures, even in the absence of acute relapse 2
This ocular motor manifestation may cause minimal symptoms but represents objective evidence of MS-related brainstem/cerebellar involvement that should be documented in her ongoing neurological care 1