Postoperative Serotonin Syndrome Following Administration of Preoperative Intrapulmonary Methylene Blue and Intraoperative Granisetron: A Case Report

BACKGROUND Methylene blue (MB), which is often used perioperatively, is a potent monoamine oxidase inhibitor that can strongly block the clearance of extracellular serotonin. Granisetron, a serotonin receptor subtype 3 (5-HT3) antagonist, is an antiemetic used to prevent or treat postoperative nausea and vomiting (PONV). Through its antagonism, granisetron can increase the extracellular serotonin concentration. Serotonin syndrome is a potentially life-threatening condition resulting from a drug reaction that affects serotonin levels. This report is of a 50-year-old woman with postoperative serotonin syndrome following co-administration of preoperative intrapulmonary methylene blue and intraoperative granisetron. CASE REPORT A 50-year-old woman with well-controlled gastroesophageal regurgitation disease presented under impression of lung cancer. She received a computed tomography (CT)-guided localization followed by video-assisted thoracic surgery under endotracheal general anesthesia. The surgery was completed uneventfully. Her postoperative course was significant for serotonin syndrome, likely triggered by co-administration of preoperative intrapulmonary MB for tumor localization and intraoperative granisetron. Other differential diagnoses were ruled out. Her management was primarily supportive, using benzodiazepine administration, and resulted in full neurologic recovery. CONCLUSIONS Intrapulmonary MB can lead to serotonin syndrome in combination with 5HT-3 antagonists when used for preoperative tumor localization. Because both MB and 5-HT3 antagonists are being widely used clinically at present, this report has highlighted that physicians, surgeons, and anesthesiologists should be aware of serotonin syndrome, its presenting features, and management, and its association with the use of methylene blue and 5-HT3 receptor antagonists, including granisetron.