Philippe Birmes and associates1 suggest that serotonin syndrome is a less serious condition than neuroleptic malignant syndrome (NMS), but this has not been our experience.2,3,4,5 In our prospective study of serotonin syndrome,4,5 6 of the 16 patients experienced disseminated intravascular coagulation (DIC), rhabdomyolysis and hypotension necessitating admission to the intensive care unit. Acute renal failure developed in 2 patients, and 1 patient died.
Table 2 in the article by Birmes and associates1 does not capture the key differences between NMS and serotonin syndrome. Both conditions can be fulminant, and patients may present with delirium, hyperthermia, rhabdomyolysis, dilated pupils, tachycardia, daphoresis, rigidity and blood pressure changes2,3,4,5 (see Table 1 with this letter). The main difference lies in the clinical gestalt: typically a patient with serotonin syndrome is agitated, speaks incoherently and has prominent myoclonus, whereas a patient with NMS is immobile, mute and staring. Although rhabdomyolysis is a complication of both toxidromes, DIC, seizures, ventricular tachycardia and severe hypotension are extremely rare in NMS.2
We agree with the mainstays of treatment suggested by Birmes and associates,1 but we also advise monitoring of vital signs, platelet count, muscle enzymes and myoglobin twice daily for at least 72 hours. We have serious concerns about the use of chlorpromazine and propranolol for serotonin syndrome. Both drugs decrease blood pressure, which will exacerbate the hard-to-treat hypotension that can occur in serotonin syndrome; in addition, chlorpromazine may precipitate NMS. An absolute contraindication for the use of propranolol is a history of asthma, which is difficult to elicit if the patient is delirious. Finally, it is important to advise patients taking serotonergic agents about the risks of this potentially serious and fulminant syndrome.
Sarah Garside Clinical Scholar Patricia I. Rosebush Associate Professor Department of Psychiatry and Behavioural Neuroscience McMaster University Hamilton, Ont.