Which medication is classically associated with nystagmus, diplopia, and extraocular muscle palsies?

Which medication is classically associated with nystagmus, diplopia, and extraocular muscle palsies?

• A. Topiramate (Topamax)
• B. Phenytoin (Dilantin)
• C. Tamoxifen (Nolvadex)
• D. Metformin (Glucophage)

Answer: (B)

Phenytoin is classically associated with ocular motor disturbances, including nystagmus, diplopia, and extraocular muscle palsies, because it can cause CNS toxicity that impairs the brainstem and cerebellar routes controlling eye movements. Nystagmus is often an early sign of phenytoin excess; as levels rise, you may see diplopia and eventually weakness or palsies of the extraocular muscles. This pattern reflects phenytoin’s effect on neuronal excitability and the ocular motor control pathways, leading to misalignment and impaired gaze. Other medications don’t fit this classic triad. Topiramate can cause vision changes and other side effects, but the combination of nystagmus with diplopia and EOM palsies is most characteristic of phenytoin toxicity. Tamoxifen can affect vision through retinopathy, and metformin is not linked to ocular motor palsies. In practice, recognizing these signs should prompt checking phenytoin levels and adjusting the dose or discontinuing if needed, along with supportive management and monitoring for other CNS symptoms.

Phenytoin is classically associated with ocular motor disturbances, including nystagmus, diplopia, and extraocular muscle palsies, because it can cause CNS toxicity that impairs the brainstem and cerebellar routes controlling eye movements. Nystagmus is often an early sign of phenytoin excess; as levels rise, you may see diplopia and eventually weakness or palsies of the extraocular muscles. This pattern reflects phenytoin’s effect on neuronal excitability and the ocular motor control pathways, leading to misalignment and impaired gaze.

Other medications don’t fit this classic triad. Topiramate can cause vision changes and other side effects, but the combination of nystagmus with diplopia and EOM palsies is most characteristic of phenytoin toxicity. Tamoxifen can affect vision through retinopathy, and metformin is not linked to ocular motor palsies.

In practice, recognizing these signs should prompt checking phenytoin levels and adjusting the dose or discontinuing if needed, along with supportive management and monitoring for other CNS symptoms.