A case of serotonin syndrome and mutism associated with methadone

A patient was seen on the palliative care service at our institution who developed serotonin syndrome and mutism associated with methadone use. Serotonin syndrome is often described as a clinical triad of mental status changes, autonomic hyperactivity, and neuromuscular abnormalities, but not all of these findings are consistently present in all patients with the disorder. The incidence of the serotonin syndrome is thought to mirror the increasing number of proserotonergic agents being used in clinical practice. In 2002, the Toxic Exposure Surveillance System, which receives case descriptions from office-based practices, inpatient settings, and emergency departments, reported 26,733 incidences of exposure to selective serotonin-reuptake inhibitors (SSRIs) that caused significant toxic effects in 7349 persons and resulted in 93 deaths. Serotonin syndrome is not an idiopathic drug reaction; it is a predictable consequence of excess serotonergic agonism of central nervous system (CNS) receptors and peripheral serotonergic receptors. The myriad of symptoms with which serotonin syndrome may present is compounded by the fact that more than 85% of physicians are unaware of serotonin syndrome as a clinical diagnosis. Other SSRIs such as fluoxetine and fluvoxamine have been shown to increase methadone plasma concentrations in dependent patients. Although the exact mechanism is unknown, there are several pathways via which a significant interaction could occur. This would include the effects methadone has on N-methyl-D-aspartate (NMDA) in addition to the impact of methadone on the cytochrome P450 enzyme system. The mainstay of treatment of serotonin syndrome is withdrawal of the offending agent and supportive care. These actions resulted in resolution of our patient's symptoms. Serotonin syndrome is becoming more common, and with the utilization of polypharmacy on many palliative care services should be considered as unifying differential diagnosis in the appropriate setting.