A 30-year-old man who was recently staed on haloperidol 30mg/day developed hyperpyrexia, muscle rigidity, akinesia, mutism, sweating, tachycardia and increased blood pressure. The investigations showed increased WBC count, increased creatinine phosphokinase. There is no history of any other drug intake or any sign of infection. The most likely diagnosis

**Core Concept**
Haloperidol-induced neuroleptic malignant syndrome (NMS) is a life-threatening, idiosyncratic reaction to antipsychotic medication, characterized by hyperpyrexia, muscle rigidity, autonomic dysfunction, and altered mental status. This condition is often associated with the blockade of dopamine receptors in the brain.

**Why the Correct Answer is Right**
The patient's symptoms are consistent with neuroleptic malignant syndrome (NMS), a rare but serious side effect of antipsychotic medications like haloperidol. The blockade of dopamine D2 receptors in the nigrostriatal pathway by haloperidol leads to an imbalance in the dopaminergic system, resulting in the characteristic symptoms of NMS. The increased creatinine phosphokinase levels indicate muscle damage, while the elevated WBC count and autonomic instability (tachycardia, increased blood pressure) further support this diagnosis.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the clinical presentation of NMS. While the patient does have autonomic instability, the combination of hyperpyrexia, muscle rigidity, and altered mental status is more consistent with NMS.
**Option B:** This option is incorrect because it suggests a diagnosis of serotonin syndrome, which is typically associated with the use of selective serotonin reuptake inhibitors (SSRIs) or serotonin-norepinephrine reuptake inhibitors (SNRIs). The patient's symptoms do not match the typical presentation of serotonin syndrome.
**Option C:** This option is incorrect because it suggests a diagnosis of malignant hyperthermia, which is a rare but life-threatening condition triggered by certain anesthetics. The patient's symptoms do not match the typical presentation of malignant hyperthermia.

**Clinical Pearl / High-Yield Fact**
Neuroleptic malignant syndrome (NMS) is a medical emergency that requires immediate recognition and treatment. It is essential to discontinue the offending medication and provide supportive care, including cooling measures, hydration, and muscle relaxation.

**Correct Answer: C. Malignant Hyperthermia.**

✓ Correct Answer: B. Neuroleptic malignant syndrome