Serotonin Syndrome (SS) is an adverse drug reaction that drives mental-status changes, autonomic hyperactivity and neuromuscular abnormalities.

Neuroleptic Malignant Syndrome (NMS) is an idiopathic reaction to dopamine-antagonist that consists of extra-pyramidal symptoms, autonomic dysfunction, hyperthermia, diaphoresis and fluctuating consciousness.

Differential diagnosis is sometimes difficult for their overlapping clinical features. Potentially lethal, both require heightened clinical awareness for prevention, recognition and prompt treatment.

Caucasian 59 years-old woman with Catatonic profile (Scored: severity-17points/ 5 screening in Bush-Francis Catatonia-Rating-Scale).

1. - Hypothyroidism

2. - Bipolar Disorder type-2 (25 years of evolution)

15 days before hospitalization, anafranil and fluoxetine treatment was replaced by Trazodone 200 mg/day and venlafaxine 150mg/day. She was also on valpromida and lorazepam 15 mg/day.

Mutism, negativism. No reaction to painful stimuli, stuporous. Diaphoresis, pallor, tremor, axial rigidity without pyramidalism (>lower limbs), high fever (40°C), tachycardia (>100lpm), rhabdomyolysis (CPK reached 17.000, 48 hours after the admission), leukocytosis, upper transaminasas, hiponatremia with hiperpotasemia.

1. - NMS: Intensity, duration and high CPK are suggestive (Sternbach). This syndrome has been described due to Venlafaxine.

2. - SS: Combination of Venlafaxine and Trazodone favors but she doesn't have acatisia, hiperreflexia, diarrhea and it wasn't resolved after 96 hours.

Drugs were removed and Lorazepam on high doses (5mg/day) was prescribed. One month later the patient was totally recovered of the episode.

If unsure diagnoses it's priority to remove the causing drugs and supportive care. Afterwards, it can be used benzodiacepines, also dantroleno in SNM.