A 59-year-old woman is brought to the emergency department by her son. He reports that his mother sounded anxious and confused on the phone. When he arrived at her home, he found her shaking, sweating profusely, and unsteady on her feet. The patient's medical problems include osteoarthritis, seasonal allergies, depression, anxiety, and chronic insomnia. She has a 25-pack-year smoking history but does not use alcohol or illicit drugs. The patient took 40 mg of fluoxetine for years with only partial improvement in her depression. However, this medication was discontinued a month ago. She was recently started on phenelzine. Her other medications include ibuprofen, diphenhydramine, and lorazepam. Temperature is 38.3 C (101 F), blood pressure is 160/90 mm Hg, pulse is 116/min, and respirations are 24/min. On examination, the patient is oriented to person and place but not time. She is agitated, diaphoretic, and tremulous. Oropharyngeal examination reveals no abnormalities; mucous membranes are dry. Cardiopulmonary examination reveals tachycardia but is otherwise normal. The patient's abdomen is soft, nontender, and nondistended with increased bowel sounds. Deep tendon reflexes are increased. Muscular strength is preserved, but there is some muscular rigidity in the lower extremities. Which of the following is the most likely diagnosis?

Question

A 59-year-old woman is brought to the emergency department by her son.  He reports that his mother sounded anxious and confused on the phone.  When he arrived at her home, he found her shaking, sweating profusely, and unsteady on her feet.  The patient's medical problems include osteoarthritis, seasonal allergies, depression, anxiety, and chronic insomnia.  She has a 25-pack-year smoking history but does not use alcohol or illicit drugs.  The patient took 40 mg of fluoxetine for years with only partial improvement in her depression.  However, this medication was discontinued a month ago.  She was recently started on phenelzine.  Her other medications include ibuprofen, diphenhydramine, and lorazepam.  Temperature is 38.3 C (101 F), blood pressure is 160/90 mm Hg, pulse is 116/min, and respirations are 24/min.  On examination, the patient is oriented to person and place but not time.  She is agitated, diaphoretic, and tremulous.  Oropharyngeal examination reveals no abnormalities; mucous membranes are dry.  Cardiopulmonary examination reveals tachycardia but is otherwise normal.  The patient's abdomen is soft, nontender, and nondistended with increased bowel sounds.  Deep tendon reflexes are increased.  Muscular strength is preserved, but there is some muscular rigidity in the lower extremities.  Which of the following is the most likely diagnosis?

Quizplus · Accepted Answer

Explanation: 11ec2b69_c1b1_3804_8f63_2fe5046ce63a_MD0005_00 This patient's anxiety, confusion, tremulousness, diaphoresis, and hyperreflexia are suggestive of serotonin syndrome (SS) that is likely due to a drug interaction between the monoamine oxidase inhibitor phenelzine and the selective serotonin reuptake inhibitor (SSRI) fluoxetine. The recommended washout period for most antidepressants prior to beginning treatment with a MAOI is 14 days. However, due to fluoxetine's long half-life, it is recommended that at least 5 weeks elapse between stopping fluoxetine and starting MAOI treatment; this patient waited only 4 weeks before initiating treatment. Symptoms of SS include a classic triad of mental status changes (eg, anxiety, delirium, confusion, restlessness), autonomic dysregulation (eg, diaphoresis, tachycardia, hypertension, hyperthermia, diarrhea, hyperactive bowel sounds, mydriasis), and neuromuscular hyperactivity (eg, hyperreflexia, tremor, rigidity, myoclonus, ocular clonus). SS is diagnosed clinically and laboratory tests are used to rule out other etiologies. SS usually occurs due to inadvertent interactions between drugs, therapeutic use of multiple serotonergic agents, or serotonergic medication overdose. Symptoms of SS (Choice A) Anticholinergic toxicity involves symptoms of dry skin, flushing, fever, mydriasis, and altered mental status. Patients may also experience urinary retention, decreased bowel sounds, autonomic instability, and tremulousness. Although this patient takes diphenhydramine, a drug with anticholinergic activity, her diaphoresis, hyperreflexia, and increased bowel sounds are consistent with SS. (Choice B) Patients in benzodiazepine withdrawal may be anxious, diaphoretic, and tremulous. However, this patient's hyperreflexia, hyperactive bowel sounds, and lower-extremity rigidity are more suggestive of SS. (Choice C) Abrupt discontinuation of SSRIs can result in a withdrawal syndrome characterized by agitation, irritability, headache, dizziness, flu-like symptoms, and paresthesias. Fluoxetine, however, is least likely to cause discontinuation symptoms due to its relatively long elimination half-life. (Choice D) Neuroleptic malignant syndrome (a rare idiosyncratic reaction to dopamine antagonists) has symptomatic similarities to SS but does not involve neuromuscular hyperactivity (eg, tremor, hyperreflexia, clonus). In addition, it is characterized by bradykinesia and generalized "lead pipe" muscular rigidity, which differs from the hyperkinesia of SS. The lack of antipsychotic exposure and the presence of tremors and hyperreflexia in this patient make SS more likely. Educational objective: Combined use of selective serotonin reuptake inhibitors (SSRIs) and monoamine oxidase inhibitors (MAOIs) can lead to serotonin syndrome, a potentially lethal condition characterized by fever, mental status changes, clonus, and hyperreflexia. Switching from fluoxetine (an SSRI) to an MAOI requires a 5-week washout. References: Overview of serotonin syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/23145389) Management of serotonin syndrome and neuroleptic malignant syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/27469512) Serotonin syndrome: preventing, recognizing, and treating it. (http://www.ncbi.nlm.nih.gov/pubmed/27824534)

A 59-Year-Old Woman Is Brought to the Emergency Department by Her