Abstract
Differential diagnosis of neuropsychiatric symptoms in a patient with an underlying malignancy is exhaustive. 5-fluorouracil (5-FU) is one of the most widely used chemotherapy agents and it is often used as the first-line regimen in head and neck malignancies. We present a case of an elderly female with an underlying locally advanced p16-positive squamous cell carcinoma of the tongue who presented with manic symptoms for one week after cycle 2 of chemotherapy. Multidisciplinary management by otorhinolaryngologists with psychiatrist and oncologist led to the cessation of 5-FU, administration of antipsychotics, and replacement with a different chemotherapy agent, leading to complete resolution of manic symptoms. Possible mechanisms of the 5-FU-induced manic episode with its treatment are discussed in this report.