Primidone/phenobarbital-induced periodic alternating nystagmus

Area of Science:

• Neurology
• Clinical Pharmacology

Background:

• Anticonvulsant medications like primidone and phenobarbital are frequently prescribed for seizure disorders.
• Drug toxicity can manifest with a range of neurological symptoms, sometimes mimicking primary neurological conditions.

Observation:

• A 37-year-old male patient with a history of seizures presented with periodic alternating nystagmus (PAN).
• The patient exhibited additional clinical signs consistent with primidone and phenobarbital toxicity.

Findings:

• The periodic alternating nystagmus (PAN) demonstrated a gradual decrease in both cycle length and intensity.
• Complete resolution of PAN and other toxicity signs was achieved following a slow tapering and discontinuation of primidone and phenobarbital.

Implications:

• This case underscores the potential for iatrogenic causes of nystagmus in patients on anticonvulsant therapy.
• Clinicians should consider drug toxicity in the differential diagnosis of new-onset nystagmus, particularly in patients with a history of seizures and those on specific medications.
• Gradual drug withdrawal is a key management strategy for resolving medication-induced neurological disturbances.