**Core Concept**
Neuroleptic malignant syndrome (NMS) is a life-threatening neurological disorder caused by an adverse reaction to certain medications, particularly antipsychotics and antiemetics. It is characterized by fever, muscle rigidity, altered mental status, and autonomic dysfunction.

**Why the Correct Answer is Right**
NMS is a result of dopamine blockade in the brain, particularly in the nigrostriatal pathway and the hypothalamus. This leads to an imbalance in the body's thermoregulation, causing fever, and an increase in muscle tone due to the blockade of dopamine receptors in the skeletal muscle. The autonomic dysfunction is thought to be due to the blockade of dopamine receptors in the hypothalamus, leading to an imbalance in the sympathetic and parasympathetic nervous system.

**Why Each Wrong Option is Incorrect**
**Option A:** Tachycardia - This is a common finding in NMS, as the autonomic dysfunction leads to an increase in sympathetic tone, causing an increase in heart rate.
**Option B:** Altered mental status - This is a hallmark of NMS, as the dopamine blockade in the brain leads to changes in consciousness and cognitive function.
**Option C:** Hypotension - This is also a common finding in NMS, as the autonomic dysfunction leads to a decrease in sympathetic tone, causing a decrease in blood pressure.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize NMS early, as it can be fatal if not treated promptly. A high index of suspicion should be maintained for patients taking antipsychotics or antiemetics who present with fever, muscle rigidity, altered mental status, and autonomic dysfunction.

**Correct Answer: D. Hypotension.**