**Question:** A 30 year old man who was recently started 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 signs of infection. The most likely diagnosis -

A. Neuroleptic Malignant Syndrome
B. Drug-induced Liver Injury
C. Drug-induced Thrombocytopenia
D. Acute Interstitial Nephritis

**Core Concept:** The Neuroleptic Malignant Syndrome (NMS) is a rare but potentially life-threatening complication of antipsychotic medication, such as haloperidol, which is a dopamine antagonist. It occurs due to the dysregulation of dopamine receptors and release, leading to autonomic instability, muscle rigidity, hyperpyrexia, and other symptoms.

**Why the Correct Answer is Right:** The correct answer is A (Neuroleptic Malignant Syndrome) because:

1. The patient developed hyperpyrexia (high fever), muscle rigidity, akinesia (inability to move), mutism (loss of speech), sweating, tachycardia (rapid heart rate), and increased blood pressure - all symptoms consistent with NMS.
2. The patient was on haloperidol, a dopamine antagonist, which is a key factor in NMS development as it disrupts the balance of dopamine levels in the brain.
3. The patient had increased white blood cell count and creatinine phosphokinase (CPK) levels, which are consistent with NMS.

**Why Each Wrong Option is Incorrect:**

A. **Drug-induced Liver Injury (Option B)** is a wrong answer because:
1. NMS is a neurological disorder, while drug-induced liver injury is a liver-related complication of medications like haloperidol. These two conditions have distinct mechanisms and clinical presentations.
2. NMS symptoms are not primarily related to liver function or injury.

B. **Drug-induced Thrombocytopenia (Option C)** is incorrect because:
1. NMS is characterized by muscle rigidity, hyperpyrexia, and autonomic instability, while thrombocytopenia refers to low platelet count, which is unrelated to NMS symptoms.
2. NMS and thrombocytopenia have different mechanisms and clinical presentations.

C. **Acute Interstitial Nephritis (Option D)** is incorrect because:
1. NMS is a neurological disorder with symptoms like muscle rigidity, hyperpyrexia, and autonomic instability, while acute interstitial nephritis is a kidney disorder unrelated to NMS symptoms.
2. NMS and acute interstitial nephritis have distinct mechanisms and clinical presentations.

D. **Neuroleptic Malignant Syndrome (Option A)** is the correct answer because:
1. NMS manifests with symptoms like muscle rigidity, hyperpyrexia, and autonomic instability, which are consistent with the disorder.
2. NMS shares