Serotonin Syndrome: Signs and Symptoms
Serotonin syndrome presents with a clinical triad of mental status changes, neuromuscular hyperactivity, and autonomic hyperactivity, typically arising within 24-48 hours after combining serotonergic medications like citalopram with lithium and aripiprazole 1, 2.
Clinical Presentation by System
Mental Status Changes
- Confusion
- Agitation
- Anxiety
- Delirium
- Hallucinations
- Coma (in advanced cases)
Neuromuscular Hyperactivity (Most Diagnostic Features)
- Clonus (spontaneous, inducible, or ocular) - highly diagnostic when present 3
- Hyperreflexia - particularly in lower extremities, more pronounced than upper extremities 3
- Tremors (high-frequency)
- Muscle rigidity (especially lower extremities)
- Myoclonus (occurs in 57% of cases - the most common finding) 3
- Incoordination
Autonomic Hyperactivity
- Hypertension (may deteriorate to hypotension)
- Tachycardia
- Arrhythmias
- Tachypnea
- Diaphoresis (profuse sweating)
- Shivering
- Hyperthermia/fever
- Mydriasis (dilated pupils)
- Flushing
Gastrointestinal Symptoms
- Nausea
- Vomiting
- Diarrhea
- Hyperactive bowel sounds
Severity Spectrum
Mild to Moderate:
- Tremor, hyperreflexia, diaphoresis, agitation
- Temperature typically ≤41.1°C 3
Severe/Life-Threatening:
- Fever >41.1°C
- Seizures
- Unconsciousness
- Rhabdomyolysis with elevated creatine kinase
- Metabolic acidosis
- Renal failure
- Disseminated intravascular coagulopathy
- Mortality rate approximately 11% 3
Critical Context for Your Patient
In a patient on aripiprazole and lithium initiating citalopram, monitor especially closely during the first 24-48 hours 1. The FDA label for citalopram specifically warns about serotonin syndrome when combined with lithium 2. While aripiprazole is not traditionally considered highly serotonergic, case reports document serotonin syndrome with aripiprazole combinations 4, 5.
Key Diagnostic Features to Assess
The presence of clonus and hyperreflexia are highly diagnostic and establish the diagnosis when occurring with serotonergic drug use 3. Look specifically for:
- Inducible clonus at the ankles
- Ocular clonus
- Hyperreflexia (test patellar and ankle reflexes bilaterally)
Timing
Symptoms typically emerge within 6-24 hours of medication initiation or dose increase 3, though the guideline states 24-48 hours for symptom onset after combining medications 1.
Important Pitfall
Physical restraints are contraindicated - they exacerbate isometric muscle contractions, worsening hyperthermia and lactic acidosis, thereby increasing mortality 3.