A 31 year old male, with mood disorder, on 30 mg of haloperidol and 100 mg of lithium, is brought to the hospital emergency room with history of acute onset of fever, excessive sweating, confusion, rigidity of limbs and decreased communication for a day. Examination reveals tachycardia and labile blood pressure and investigations reveal increased CPK enzyme levels and lecocytosis. He is likely to have developed.

**Core Concept**
The patient's symptoms and lab results suggest a life-threatening condition that occurs as a side effect of antipsychotic medication, particularly haloperidol, and lithium. This condition is characterized by muscle rigidity, fever, altered mental status, and elevated CPK levels, indicating muscle damage.

**Why the Correct Answer is Right**
The patient is likely experiencing Neuroleptic Malignant Syndrome (NMS), a rare but potentially fatal condition. NMS is thought to occur due to an idiosyncratic reaction to antipsychotic medications, leading to an imbalance in dopamine and serotonin levels in the brain. This imbalance results in increased muscle tone, fever, and altered mental status. The elevated CPK levels are indicative of muscle damage, and leucocytosis is a non-specific indicator of inflammation.

**Why Each Wrong Option is Incorrect**
**Option A:** While serotonin syndrome can present with fever and altered mental status, it typically lacks the significant muscle rigidity and elevated CPK levels seen in NMS.

**Option B:** Catatonia is a condition characterized by immobility, rigidity, and altered mental status, but it is not typically associated with fever, leucocytosis, or elevated CPK levels.

**Option C:** Malignant Hyperthermia is a condition that occurs in response to certain anesthetics and is characterized by muscle rigidity, fever, and elevated CPK levels. However, it is not typically associated with altered mental status or leucocytosis.

**Clinical Pearl / High-Yield Fact**
Early recognition and discontinuation of the offending medication are critical in the treatment of NMS. The patient should be immediately removed from haloperidol and lithium, and supportive care, including hydration and cooling measures, should be initiated.

**Correct Answer: C. Malignant Hyperthermia

✓ Correct Answer: C. Neuroleptic malignant syndrome