Okay, let's tackle this question. The patient is on trifluoperazine, which I remember is a typical antipsychotic. The symptoms are hyperthermia, lethargy, and sweating. Hmm, those sound like neuroleptic malignant syndrome (NMS) symptoms. NMS is a serious condition associated with antipsychotic use, right? So the question is about what investigations are needed here.

First, the core concept is NMS. The key features include hyperthermia, muscle rigidity, altered mental status, and autonomic instability. The underlying mechanism involves dopamine receptor blockade, leading to hypothalamic dysfunction and muscle rigidity causing rhabdomyolysis. So the investigations should look for signs of rhabdomyolysis and other metabolic derangements.

The correct answer would probably involve checking CPK levels because elevated creatine phosphokinase (CPK) is a hallmark of muscle breakdown. Also, electrolyte imbalances like hyperkalemia, hypocalcemia, and metabolic acidosis are common. Maybe a CBC and renal function tests too, since rhabdomyolysis can lead to acute kidney injury.

Now, looking at the incorrect options. If the options included things like liver function tests or lipid profile, those aren't directly related to NMS. Similarly, maybe a chest X-ray or ECG could be distractors but aren't the primary tests here. The key is to focus on muscle enzymes and electrolytes.

The clinical pearl here is to remember that NMS is a medical emergency requiring immediate discontinuation of the antipsychotic, supportive care, and possibly dopamine agonists like bromocriptine. The mnemonic for NMS symptoms is "Fever, Flexed posture, Lead-pipe rigidity, Autonomic instability." But the main investigations are CPK, electrolytes, renal function, and CBC.

**Core Concept**
Neuroleptic malignant syndrome (NMS) is a life-threatening complication of antipsychotic use, including trifluoperazine, characterized by hyperthermia, muscle rigidity, altered mental status, and autonomic instability. It results from dopamine receptor blockade in the hypothalamus and basal ganglia, leading to rhabdomyolysis and metabolic derangements.

**Why the Correct Answer is Right**
The correct investigation focuses on detecting rhabdomyolysis and metabolic abnormalities. Elevated **creatine phosphokinase (CPK)** confirms muscle breakdown, while electrolytes (e.g., hyperkalemia, hypocalcemia) and renal function tests identify complications like acute kidney injury. Complete blood count (CBC) and urinalysis may reveal myoglobinuria. Early diagnosis via these tests is critical for timely management.

**Why Each Wrong Option is Incorrect**
**Option A:** Liver function tests are irrelevant unless hepatotoxicity is suspected, which is not indicated here.
**Option B:** Lipid profile has no role in NMS evaluation.
**Option C:** Echocardiography is unnecessary unless cardiac involvement is suspected, which is not a primary concern in NMS.

**Clinical Pearl / High-Yield Fact**
Remember the "Fever, Flexed posture, Lead-pipe rigidity, Autonomic instability" (FFLA) mnemonic for NMS. Always discontinue antipsychotics immediately and consider bromocriptine or amantadine as

✓ Correct Answer: D. Hemogram, CPK and renal function test