A 68-year-old man with a history of benign prostatic hyperplasia and chronic angle-closure glaucoma presents to the emergency department with acute urinary retention and severe eye pain. His son reports that the patient was prescribed a new medication for myasthenia gravis 2 days ago. On examination, blood pressure is 145/92 mmHg, heart rate 58 bpm, and pupils are constricted. The patient is diaphoretic and has visible muscle fasciculations. Which of the following drugs most likely caused this clinical presentation?

Explanation

## Clinical Scenario Analysis The patient presents with a **cholinergic crisis** — a state of excessive cholinergic stimulation caused by overstimulation of muscarinic and nicotinic receptors. ### Key Clinical Features **Muscarinic manifestations:** - Constricted pupils (miosis) - Severe eye pain (angle-closure glaucoma exacerbation) - Acute urinary retention (paradoxical — excessive parasympathetic tone causes detrusor contraction but sphincter spasm) - Diaphoresis - Bradycardia - Hypertension (initial phase) **Nicotinic manifestations:** - Muscle fasciculations - Weakness (progressing to paralysis if untreated) ### Why Neostigmine? **Key Point:** Neostigmine is an acetylcholinesterase inhibitor used to treat myasthenia gravis. It prolongs the action of acetylcholine at the neuromuscular junction by preventing its enzymatic breakdown. **High-Yield:** In myasthenic patients, the therapeutic window is narrow. Overdosing or prolonged use can cause **cholinergic crisis** — characterized by: 1. Excessive muscarinic effects (SLUDGE: Salivation, Lacrimation, Urination, Defecation, GI upset, Emesis) 2. Excessive nicotinic effects (fasciculations, weakness, paralysis) 3. CNS effects (confusion, seizures in severe cases) The patient's pre-existing angle-closure glaucoma is a **contraindication** to cholinergic drugs because miosis (pupil constriction) can precipitate acute angle closure by pushing the iris forward and obstructing aqueous humor drainage. ### Management of Cholinergic Crisis ```mermaid flowchart TD A[Suspected Cholinergic Crisis]:::outcome --> B[Stop anticholinesterase immediately]:::action B --> C[Atropine IV 0.5-1 mg]:::action C --> D{Respiratory compromise?}:::decision D -->|Yes| E[Intubation + mechanical ventilation]:::action D -->|No| F[Supportive care, monitor]:::action E --> G[Pralidoxime 1-2 g IV if nicotinic signs persist]:::action F --> G G --> H[Reassess and titrate]:::action ``` **Clinical Pearl:** Atropine (muscarinic antagonist) is the first-line antidote for cholinergic crisis. Pralidoxime (oxime) reactivates acetylcholinesterase and is used for nicotinic signs if atropine alone is insufficient. **Warning:** Do NOT confuse cholinergic crisis with myasthenic crisis (weakness due to insufficient acetylcholine). Both present with weakness, but the former has excessive parasympathetic signs and the latter does not. ## Differential: Myasthenic vs. Cholinergic Crisis | Feature | Myasthenic Crisis | Cholinergic Crisis | |---------|-------------------|--------------------| | **Cause** | Insufficient acetylcholine | Excess acetylcholine | | **Pupils** | Normal or dilated | Constricted (miosis) | | **Salivation** | Absent | Profuse | | **Sweating** | Absent | Marked (diaphoresis) | | **Fasciculations** | Absent | Present | | **Response to edrophonium** | Improvement | Worsening | | **Treatment** | Increase anticholinesterase | Atropine + stop drug | [cite:KD Tripathi 8e Ch 6]