Serotonin syndrome presenting as severe reversible cerebral vasoconstriction syndrome

Serotonin syndrome is a life-threatening adverse drug reaction caused by excessive serotonergic activity from therapeutic use, overdose or drug interactions. Its recognition is challenging, as manifestations range from subtle to severe and fatal. Key diagnostic features are autonomic dysfunction, motor hyperactivity and exaggerated reflexes, including clonus. We report a young woman with severe serotonin syndrome due to serotonergic polypharmacy who developed reversible cerebral vasoconstriction syndrome and overlapping posterior reversible encephalopathy syndrome. The diagnosis was initially delayed because attention had focused on her prominent vascular features with severe focal neurological deficits rather than the underlying toxidrome. We diagnosed serotonin syndrome as she developed more characteristic features. This case highlights the importance of considering serotonin syndrome in patients receiving serotonergic medications who develop motor findings, autonomic dysfunction or unexplained neurological deterioration.