Multiple Sclerosis is Most Likely
The jerking movement of the eyes on lateral gaze described in this question is gaze-evoked nystagmus, which is most characteristic of Multiple Sclerosis (MS) among the options provided. 1
Clinical Reasoning
Why MS is the Answer
Gaze-evoked nystagmus is a central form of nystagmus indicating brainstem or cerebellar pathology, which are heavily myelinated regions characteristically affected by MS demyelinating lesions, occurring in approximately 13.5% of MS patients. 1
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 ocular motor dysfunction. 1
Gaze-evoked nystagmus is one of the most frequent chronic ocular motor manifestations in MS, along with internuclear ophthalmoplegia and saccadic hypermetria. 2
In a bedside examination study of 163 MS patients, gaze-evoked nystagmus was present in 13.5% of patients, making it one of the most common findings. 3
Why the Other Options Are Incorrect
Myasthenia Gravis:
- Nystagmus is not a typical feature of myasthenia gravis, which characteristically produces fatigable weakness that worsens with sustained gaze. 1
- Myasthenia presents with variable ptosis, diplopia that changes over the course of examination, and positive ice test—not jerking eye movements on lateral gaze. 4
Graves' Disease (Thyroid Eye Disease):
- Thyroid eye disease causes restrictive esotropia and limitation of ocular rotations due to extraocular muscle enlargement and fibrosis. 5, 1
- It does not produce gaze-evoked nystagmus as a characteristic finding. 1
- The restriction is mechanical, not a central neurological phenomenon. 5
Neurofibromatosis:
- While neurofibromatosis can cause optic pathway gliomas and other CNS tumors, it does not characteristically produce gaze-evoked nystagmus. 1
- Tumors causing nystagmus would more likely produce other focal neurological signs beyond isolated gaze-evoked nystagmus. 1
Cluster Headache:
- Cluster headache is a primary headache disorder without characteristic ocular motor findings like gaze-evoked nystagmus.
Clinical Significance
Ocular motor disorders are frequently underdiagnosed in MS if not specifically examined, with overall prevalence of at least one eye movement abnormality in 68.1% of MS patients. 3
Patients with ocular motor disorders in MS have more severe disability (P = 0.0005) and more frequently show infratentorial MRI lesions (P = 0.004). 3
MS lesions in the vestibulocerebellum, brainstem, thalamus, and basal ganglia lead to abnormalities of gaze, saccades, pursuit, and nystagmus identifiable on eye examination. 6
Key Examination Pitfall
The high prevalence of ocular motor manifestations in MS emphasizes the importance of systematic neuro-ophthalmological examination, as chronic manifestations may cause minimal or no symptoms despite being present on examination. 2