Refining the Clinical Features of Serotonin Syndrome: A Prospective Observational Study of 45 Patients

INTRODUCTION: Serotonin syndrome (SS) is a drug-induced clinical syndrome that results from the excess intrasynaptic concentration of serotonin. Prospective observations are limited for SS. METHODS: We prospectively recruited 45 consecutive adult patients (>18 years) fulfilling the Hunter's criteria for SS. All patients were subjected to a detailed clinical history and examinations. Patients were subjected to appropriate investigations to find out the other causes. The causation of SS to serotonergic drugs was assessed according to Naranjo adverse drug reaction probability scale. RESULTS: The mean age was 37.3 years (range: 18–59 years). Sixty-two percent of patients were male. There were 15 different underlying clinical syndromes for which serotonergic drugs were started. Psychiatry conditions (36%) and cough/respiratory tract infection (16%) were the two most common clinical conditions for starting serotonergic drugs. We noted 49 different symptoms and physical signs. Overall, tremor (78%) and dizziness (47%) were the two most common symptoms. Headache (16%) and dizziness (16%) were the two most common initial (or first) symptoms. However, gait difficulty and febrile encephalopathy were the two most common reasons to visit the hospital. We noted 18 different drugs causing SS. Thirty-eight percent of patients received single serotonergic agent antidepressants, pain medicines and cough syrups were other important drugs causing SS. CONCLUSIONS: This study represents the largest clinic-based study on SS. SS is not rare in clinical practice. However, various aspects of this syndrome are still to be determined. All patients on serotonergic drugs should be physically examined for the presence of SS on the development of any new symptom.