| To obtain emergency consultation with a medical toxicologist, in the United States, call 1-800-222-1222 for the nearest regional poison control center. Contact information for poison control centers around the world is available at the WHO website and in the UpToDate topic on regional poison control centers (society guideline links). |
| Clinical and laboratory features |
| The Hunter Criteria for SS are fulfilled if the patient has taken a serotonergic agent and has one of the following: |
| Spontaneous clonus |
| Inducible clonus and agitation or diaphoresis |
| Ocular clonus and agitation or diaphoresis |
| Tremor and hyperreflexia |
| Hypertonia |
| Temperature above 38°C and ocular clonus or inducible clonus |
| SS is a clinical diagnosis; no laboratory test can confirm the diagnosis. SS can manifest a wide range of clinical symptoms from mild tremor to life-threatening hyperthermia and shock. |
| Examination findings can include: hyperthermia, agitation, ocular clonus, tremor, akathisia, deep tendon hyperreflexia, inducible or spontaneous clonus, muscle rigidity, dilated pupils, dry mucus membranes, increased bowel sounds, flushed skin, and diaphoresis. Neuromuscular findings are typically more pronounced in the lower extremities. |
| The following tests may be helpful in severe cases of SS to narrow the differential and to monitor potential complications: |
| Complete blood count, basic electrolytes, creatinine, and blood urea nitrogen |
| Creatine phosphokinase, hepatic transaminases, coagulation studies |
| Blood culture, urinalysis, urine culture |
| Chest radiograph |
| Head computed tomography, lumbar puncture |
| Differential diagnosis |
| Neuroleptic malignant syndrome |
| Anticholinergic toxicity |
| Malignant hyperthermia |
| Sympathomimetic toxicity |
| Meningitis or encephalitis |
| Treatment |
| Discontinue serotonergic agents |
| Sedate using benzodiazepines (eg, lorazepam 1 to 2 mg IV per dose; 0.02 to 0.04 mg/kg per dose in children): goal is to eliminate agitation, neuromuscular abnormalities (eg, tremor, clonus), and elevations in heart rate and blood pressure; titrate dose to effect |
| Provide: oxygen (maintain SpO2 ≥94); IV fluids; continuous cardiac monitoring |
| Anticipate complications; in severe SS vital signs can fluctuate widely and rapidly |
| If benzodiazepines and supportive care fail to improve agitation and abnormal vital signs, give cyproheptadine (12 mg orally or by orogastric tube for initial adult dose; pediatric doses included in main text) |
| Treat patients with temperature >41.1°C with immediate sedation, paralysis, and endotracheal intubation; treat hyperthermia with standard measures; avoid antipyretics such as acetaminophen |
