Fluoxetine-Induced Atypical Serotonin Syndrome with Hallucinations Masquerading as a Parkinsonian Syndrome

Objective: To report a unique case of fluoxetine overdose leading to serotonin syndrome with auditory and complex visual hallucinations. This case also demonstrates serotonin syndrome may mimic a Parkinsonian syndrome, which is poorly described in the literature. Case Summary: A 65-year-old gentleman, undergoing evaluation for possible Parkinsonian syndrome with bradykinesia and rigidity presented to the emergency department with additional complaints of weakness, fatigue, flushing, and complex visual and auditory hallucinations. Chart review revealed he was unintentionally overdosed with fluoxetine to a total daily dose of 160 mg. Examination revealed tachycardia, diaphoresis, significant mydriasis, and visual hallucinations. Initial workup was unremarkable. Poison control recommended discontinuation of the fluoxetine and in follow up he reported resolution of all symptoms. Discussion: This case describes serotonin syndrome as the result of chronic fluoxetine overdose masquerading as a Parkinsonian syndrome. This patient also experienced auditory and visual hallucinations that resolved with cessation of fluoxetine, adverse effects which are relatively uncommon. The likelihood the patient’s symptoms were the result of fluoxetine intoxication is probable, as assessed by the Naranjo Adverse Drug Reaction (ADR) probability scale. Conclusions: Chronic fluoxetine overdose can lead to serotonin syndrome, as well as, several rare adverse effects including a Parkinsonian syndrome, complex visual, and auditory hallucinations. A high index of suspicion is necessary for diagnosis of serotonin syndrome, particularly in mild cases. Most cases can be prevented with careful medication reconciliation.