Regarding neuroleptic malignant syndrome (NMS), all of the following statements are correct EXCEPT:

Explanation

## Neuroleptic Malignant Syndrome (NMS): Clinical Features and Pathophysiology **Key Point:** NMS is a life-threatening idiosyncratic reaction to dopamine antagonists characterized by the tetrad of **hyperthermia, muscle rigidity, altered mental status, and autonomic instability**. Diarrhea is NOT typical — constipation is the expected GI manifestation. ### Classic Tetrad of NMS | Component | Clinical Feature | |---|---| | **Hyperthermia** | Often >39°C, can exceed 40°C; unresponsive to antipyretics | | **Muscle Rigidity** | Lead-pipe (uniform resistance throughout ROM) or waxy flexibility | | **Altered Mental Status** | Confusion, disorientation, stupor, coma | | **Autonomic Instability** | Tachycardia, hypertension, tachypnea, diaphoresis | ### Gastrointestinal Manifestations: NMS vs. Serotonin Syndrome | Condition | GI Pattern | |---|---| | **NMS** | Constipation (due to anticholinergic effects of antipsychotics + immobility) | | **Serotonin Syndrome** | Diarrhea (due to enhanced 5-HT activity in enteric nervous system) | **High-Yield:** This GI difference is a high-yield discriminator on exams. NMS → constipation; serotonin syndrome → diarrhea. ### Pathophysiology Acute dopamine blockade in the hypothalamus and basal ganglia → loss of thermoregulatory control + loss of dopaminergic inhibition of muscle tone → hyperthermia + rigidity. The mechanism is NOT fully understood (idiosyncratic, not dose-dependent). ### Risk Factors for NMS - **Drug-related:** High-potency typical antipsychotics (haloperidol, fluphenazine) > atypical antipsychotics; rapid dose escalation; parenteral administration - **Patient-related:** Male gender, young age, dehydration, agitation, previous NMS episode - **Environmental:** High ambient temperature ### Triggers Beyond Antipsychotics 1. **Metoclopramide** (dopamine antagonist, commonly used for nausea) 2. **Domperidone** (peripheral dopamine antagonist, used in India for GI motility) 3. **Lithium** (rare, may lower seizure threshold and increase NMS risk) 4. **Reserpine** (depletes catecholamines) 5. **Abrupt withdrawal** of dopamine agonists (L-DOPA in Parkinson's disease) **Clinical Pearl:** NMS can occur even with atypical antipsychotics (risperidone, olanzapine, quetiapine), though the incidence is lower than with typical antipsychotics. This is a common exam trap — do not assume NMS only occurs with typical antipsychotics. ### Diagnostic Criteria (Modified DSM-5) 1. Exposure to dopamine antagonist within 72 hours 2. Hyperthermia (≥38.5°C) 3. Muscle rigidity 4. Altered mental status 5. Elevated CK (>1000 IU/L, often >4000 IU/L) 6. Absence of other causes (infection, malignancy, toxins) ### Laboratory Findings in NMS - **Elevated CK:** Indicates rhabdomyolysis; CK >1000 IU/L is diagnostic; can exceed 10,000 IU/L - **Myoglobinuria:** Dark (cola-colored) urine; indicates muscle breakdown - **Elevated LDH, AST, ALT:** Reflect muscle and hepatic injury - **Leukocytosis:** WBC often 10,000–20,000/μL - **Hypokalemia, hypocalcemia:** Secondary to rhabdomyolysis ### Management Algorithm ```mermaid flowchart TD A[Suspected NMS: Fever + Rigidity + Altered MS + Autonomic Instability]:::outcome --> B[Stop dopamine antagonist immediately]:::action B --> C[Supportive care: IV fluids, cooling measures]:::action C --> D[Check CK, myoglobin, renal function, electrolytes]:::action D --> E{CK >1000 or clinical deterioration?}:::decision E -->|Yes| F[Dantrolene 1 mg/kg IV q 5-10 min up to 10 mg/kg]:::action E -->|Yes| G[Bromocriptine 2.5-5 mg PO/NG q 6-8 h]:::action E -->|No| H[Supportive care + monitor]:::action F --> I[Monitor for rhabdomyolysis complications]:::action G --> I H --> I I --> J{Urine myoglobin present or CK rising?}:::decision J -->|Yes| K[Aggressive hydration, alkalinize urine, monitor renal function]:::action J -->|No| L[Gradual recovery over days to weeks]:::outcome K --> L ``` **Warning:** Do NOT give antipyretics (acetaminophen, NSAIDs) — they are ineffective in NMS and may mask fever. Cooling measures (ice packs, cooling blankets) are the standard. ### Pharmacological Treatment | Agent | Mechanism | Dosing | Evidence | |---|---|---|---| | **Dantrolene** | Inhibits Ca²⁺ release from sarcoplasmic reticulum; reduces muscle rigidity | 1 mg/kg IV q 5–10 min, max 10 mg/kg/day | Reduces mortality; first-line for severe NMS | | **Bromocriptine** | Dopamine agonist; restores dopaminergic tone | 2.5–5 mg PO/NG q 6–8 h | Reduces duration; adjunct to dantrolene | | **Lorazepam** | Benzodiazepine; reduces agitation and muscle tone | 1–2 mg IV/IM q 2–4 h | Supportive; helps with agitation | ### Serotonin Syndrome vs. NMS: Key Discriminators | Feature | Serotonin Syndrome | NMS | |---|---|---| | **Onset** | Hours to 24 hours | 24 hours to weeks | | **Trigger** | Serotonergic drugs (SSRIs, MAOIs, tramadol) | Dopamine antagonists (antipsychotics, metoclopramide) | | **Clonus** | Present (highly specific) | Absent | | **GI symptoms** | Diarrhea | Constipation | | **Rigidity type** | Variable | Lead-pipe | | **CK elevation** | Mild to moderate | Often marked (>4000 IU/L) | | **Mydriasis** | Present | Normal pupils | | **Resolution** | Hours to days after drug discontinuation | Days to weeks | **Tip:** On exam, if you see "diarrhea" in an NMS question, it's likely a distractor. NMS → constipation; serotonin syndrome → diarrhea.