High-Yield Spontaneous Nystagmus
Spontaneous nystagmus occurs when a patient is at rest with their head in the neutral position. Differentiating whether the root cause is peripheral (inner ear/vestibular nerve) or central (brainstem/cerebellum) is a favorite clinical target for board examinations.
Peripheral vs. Central Spontaneous Nystagmus
| Feature | Peripheral Vestibular | Central Nervous System |
|---|---|---|
| Direction of Fast Phase | Unidirectional (beats away from the side of the lesion). | Can be bidirectional or change direction with gaze. |
| Type of Movement | Combined horizontal and torsional. **Never purely vertical or purely torsional.** | Can be purely vertical (upbeat/downbeat) or purely torsional. |
| Effect of Visual Fixation | Suppressed/inhibited by visual fixation. | Not suppressed (may even break out or worsen). |
| Associated Symptoms | Severe vertigo, autonomic symptoms (nausea/vomiting), tinnitus, or hearing loss. | Milder vertigo; prominent neurological signs (dysmetria, ataxia, cranial nerve deficits). |
| Alexander’s Law | Follows the law (amplitude increases when gazing in the direction of the fast phase). | Does not consistently obey Alexander’s law. |
NEET PG “Must-Know” Clinical Pathology
- Vestibular Neuritis: Acute onset of severe, prolonged peripheral spontaneous nystagmus beating toward the healthy ear. Auditory function remains completely intact.
- Labyrinthitis: Presents identically to vestibular neuritis but includes **unilateral sensorineural hearing loss** and tinnitus due to involvement of both branches of CN VIII.
- Downbeat Nystagmus: Highly localizing to the craniocervical junction (e.g., Chiari malformation, cerebellar vermis lesions).
- Upbeat Nystagmus: Commonly associated with lesions in the medulla or pontomedullary junction.
- Fixation Disinhibition: Because peripheral nystagmus is suppressed by looking at a fixed object, clinicians use Frenzel glasses (which prevent visual fixation) to accurately observe it.