Case report
A 60-year-old drug-addict man was admitted to poisoning department of loghman hospital with dizziness, nausea, and vomiting. The patient’s medical history was bipolar disorder and mental disability. In past drug history, he used lithium (300 mg once daily), Clonazepam (2 mg at bedtime), valproate sodium (500 mg twice a day), perphenazine (8 mg at bedtime)and methadone (unknown dose). On examination, his blood pressure was 95/61 mmHg, heart rate 110 bpm, respiratory rate 7  breaths per minute and meiotic pupils with negative neurological examination.
On admission, the patient was unconscious and did not respond to painful stimulation. Laboratory findings included white blood cell count 14.2 × 109 /l, platelet 183 × 109 /l, creatinine 6.8 mg/dl, potassium 7.3 mg/dl, CPK 4218 U/l and lactic acidosis. Drug concentration in serum included lithium 2.6 mEq/L (therapeutic level: 0.6-1.2 mEq/L) and valproate sodium 217.6 µg/ml (therapeutic level: 50-120 µg/ml) and toxicology urine test was positive for methadone and benzodiazepine and negative for tramadol and cannabinoids. Except for methadone, other patients drugs were placed on hold. A jugular catheter was inserted and the patient underwent hemodialysis for 3.5 hours in the emergency department then patient was intubated and transferred to the intensive care unit.
On the third day of hospitalization, the patient was febrile (38.8°C) and the chest X-ray revealed a bilateral opacities while computed tomography displayed consolidation and ground glass opacities (posterior segment of the upper lobes) in both pulmonary field, so empiric antibiotics for aspiration pneumonia (ceftriaxone 1000 mg twice a day intravenously and clindamycin 600 mg three times a day intravenously) was initiated immediately. Blood and urine culture after 3 days was negative but sputum culture was positive for Staphylococcus aureus (105 CFU/cell). In antibiogram, the microorganism is resistant to clindamycin and trimethoprim-sulfamethoxazole. Based on sputum culture and resistance pattern, antibiotics changed to linezolid 600 mg twice a day intravenously. However, two days after the initiation of linezolid the patient began to run a fever (39°C) with agitation, tremor, spontaneous clonus movement in hands and tachycardia (pulse rate 115/min). Complete workup was performed that chest X-ray did not change from before and urine analysis did not show any abnormality. In addition, there was also no evidence of seizures on the Electroencephalogram (EEG) and the findings of a brain CT scan were normal. Due to these manifestations, the first diagnosis for the patient was serotonin syndrome Based on hunter criteria (sensitive and specific criteria for diagnosis serotonin toxicity) [9]. Hunter’s diagnostic criteria include at least one of the following features: spontaneous clonus; inducible clonus with agitation or diaphoresis; ocular clonus with agitation or diaphoresis; tremor and hyperreflexia; or hypertonia, temperature above 100.4°F (38°C), and ocular or inducible clonus. There is no particular laboratory test for diagnosis of serotonin syndrome but in some literature, an elevation of the total creatine kinase and transaminase levels and leukocytosis have been reported [10, 11]. In treatment of SS, linezolid administration was promptly discontinued and vancomycin therapy was initiated (1000 mg twice a day intravenously). Supportive therapies including hydration (3 liter of electrolytic solution every 24 hours, metoclopramide 10 mg three times a day intravenously), cyproheptadine 4 mg three times a day via nasogastric tube and benzodiazepine for agitation were performed. Tremor, rigidity and clonus movement disappeared within 48 hours. The patient clinical situation improve but the level of consciousness was not different from before. The patient’s hemodynamic status stabilized, and the course of antibiotic treatment was completed.
Finally, the patient was extubated after one week and transferred to the ward under stable condition.