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Phenytoin-induced ophthalmoplegia
Neurology
|November 1, 1976
Summary
Phenytoin (an anti-seizure medication) can cause total external ophthalmoplegia, a condition where eye movements are lost. This adverse effect is linked to high phenytoin blood levels and may involve its action on brain pathways controlling eye reflexes.
Area of Science:
- Neuroscience
- Pharmacology
- Ophthalmology
Background:
- Phenytoin is a widely used anti-seizure medication.
- Adverse neurological effects of phenytoin can occur, particularly at high serum concentrations.
Observation:
- Five patients developed total external ophthalmoplegia after receiving phenytoin.
- Ophthalmoplegia was associated with altered consciousness (drowsiness to coma) and high phenytoin blood levels (36-55 mug/mL).
- Initial eye movements were absent, unresponsive to oculocephalic and oculovestibular stimuli.
Findings:
- Complete loss of horizontal and vertical eye movement was observed.
- Recovery of vestibulo-ocular reflexes lagged behind the return of consciousness and other neurological functions.
- High phenytoin levels correlate with severe ophthalmoplegia.
Implications:
- Phenytoin-induced ophthalmoplegia highlights potential neurotoxicity of the drug.
- The mechanism may involve phenytoin's potentiation of inhibitory neurotransmission (GABA) in the vestibulo-oculomotor pathway.
- Understanding this adverse effect is crucial for patient monitoring and drug safety protocols.