LAUSR

To the Editor: Phenytoin is a common anticonvulsant and it acts by blocking the voltage dependent block of voltage gated sodium channels.1 Phenytoin is mainly metabolized in the liver by CYP2C9 and individuals with impaired excretory or metabolic pathways may be at increased risk for early signs of toxicity.2,3 Common side effects involving the central nervous system include, ataxia, cerebral atrophy, cerebral dysfunction, headaches, insomnia, confusion, neuropathy and vertigo.1 Dyskinesia is a rare side effect. It has been proposed that prolonged or high dosage phenytoin can increases dopaminergic and serotonergic pathways in the brain, which may play a role in chorea.4 The unpredictable, involuntary movements of the condition are a result of damage or dysfunction of the indirect and direct pathways of the circuitry.2 This rare side effect has mainly been observed in children, we present a rare case of phenytoin-induced chorea in an adult. 66-year -old gentleman with past medical history significant for coronary artery disease, diabetes mellitus type 2, and osteomyelitis presented to the hospital due to a draining wound on his left foot. His vital signs were significant for blood pressure of 110/53 mm Hg, temperature of 36.3°C, pulse of 86 beats per minute. Physical exam was remarkable for lethargy, swollen left foot with an ulcer on lateral dorsal surface of the foot. The left foot was also tender and warm on palpation. The patient’s WBC was 16.1 10 3 3/mL, and his lactic acid was 1.6 mmol/L. Blood cultures were collected and the patient was treated with Vancomycin and Piperacillin/Tazobactam. An MRI of the foot showed osteomyelitis and the patient was taken to operating room for a below knee amputation. His lethargy did not improve post operatively, a subsequent CT head and MRI brain did not show any acute changes, and neurology was consulted. EEG showed seizure-like activity, and patient was started on Phenytoin. After Phenytoin was started, patient started to experience choreiform movements, eliciting repetitive, jerky, involuntary movements in all extremities. Phenytoin levels were drawn and were therapeutic during the hyperkinetic movements. These were thought to be secondary to phenytoin, and thus it was discontinued. After a few days of discontinuance the choreiformmovements stopped. Patient was instead started on Levetriacetam, which improved his encephalopathy. Phenytoin induced chorea is mainly seen in children and literature review did not reveal any case reports showing such manifestation of phenytoin adverse reaction in adults .60 years age.5 We attribute our patient’s dyskinesia as an adverse reaction from phenytoin. Hence it was a probable adverse drug reaction based on Naranjo’s scale (score of 5), since the reaction followed a reasonable temporal sequence after the drug was started and it was confirmed by withdrawal of the drug. In our case we would like to emphasize that the phenytoin induced dyskinesia should be high on the differential in patients who develop choreiform movements and are on phenytoin. Therefore, phenytoin should be used cautiously in patients with history of movement disorders or when used in combination with other agents known to cause movement disorders.