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Downbeat nystagmus with phenytoin
Journal of Clinical Neuro-Ophthalmology
|September 1, 1982
Summary
Downbeat nystagmus, typically from structural issues, can rarely stem from drug toxicity. This study shows phenytoin (Dilantin) intoxication caused downbeat nystagmus in two patients, resolving upon drug level normalization.
Area of Science:
- Neurology
- Ophthalmology
- Toxicology
Background:
- Downbeat nystagmus (DBN) is an involuntary eye movement disorder.
- DBN is most commonly associated with structural lesions at the craniocervical junction.
- Metabolic diseases and drug intoxication are rare causes of DBN.
Observation:
- Two patients presented with downbeat nystagmus.
- Both patients exhibited symptoms of phenytoin-induced central nervous system dysfunction.
- Toxic blood levels of phenytoin (greater than 20 micrograms/ml) were confirmed.
Findings:
- Phenytoin (Dilantin) intoxication was identified as the cause of downbeat nystagmus in these cases.
- Complete resolution of DBN occurred after phenytoin blood levels returned to the therapeutic range.
- This highlights a reversible cause of DBN.
Implications:
- Phenytoin intoxication should be considered in the differential diagnosis of downbeat nystagmus.
- Monitoring phenytoin levels is crucial for patients presenting with DBN and relevant symptoms.
- Early diagnosis and management of drug toxicity can lead to complete recovery of nystagmus.