A 34-year-old woman from Delhi presents with a 3-month history of progressive ptosis and diplopia. Symptoms worsen towards the evening and improve after rest. On examination, she has bilateral ptosis that worsens with sustained upward gaze for 30 seconds. Serum anti-acetylcholine receptor (AChR) antibodies are positive. She is started on pyridostigmine. However, 2 weeks later, she develops acute worsening of muscle weakness, respiratory distress, and increased salivation despite compliance with medication. What is the most likely diagnosis of her acute deterioration?

Explanation

## Diagnosis: Cholinergic Crisis **Key Point:** Cholinergic crisis is an acute, life-threatening complication of excessive anticholinesterase therapy in myasthenia gravis (MG) patients. It presents with acute worsening of weakness paradoxically caused by overdose of pyridostigmine. ### Clinical Features of Cholinergic Crisis | Feature | Cholinergic Crisis | Myasthenic Crisis | |---------|-------------------|-------------------| | **Cause** | Excess anticholinesterase (pyridostigmine overdose) | Inadequate treatment or precipitant (infection, stress) | | **Onset** | Hours to days after dose increase | Gradual or acute | | **Muscle weakness** | Worsens acutely | Worsens acutely | | **Salivation** | Increased (muscarinic effect) | Normal | | **Pupil size** | Miosis (pinpoint pupils) | Normal | | **GI symptoms** | Diarrhoea, nausea, vomiting | Absent | | **Fasciculations** | Present (visible muscle twitching) | Absent | | **Response to edrophonium** | Worsens weakness | Improves weakness | **High-Yield:** The **SLUDGE mnemonic** helps identify cholinergic excess: - **S**alivation (increased) - **L**acrimation - **U**rination (incontinence) - **D**efecation (diarrhoea) - **G**astric upset - **E**mesis ### Clinical Pearl The presence of **increased salivation** in this case is a red flag for cholinergic crisis, not myasthenic crisis. Myasthenic crisis presents with pure motor weakness without autonomic features. ### Management Algorithm ```mermaid flowchart TD A[Acute worsening of MG weakness]:::outcome --> B{Clinical features?}:::decision B -->|Salivation, miosis, fasciculations| C[Cholinergic Crisis]:::urgent B -->|Pure muscle weakness, no autonomic signs| D[Myasthenic Crisis]:::urgent C --> E[STOP anticholinesterase immediately]:::action C --> F[Supportive care, mechanical ventilation if needed]:::action C --> G[Atropine for muscarinic symptoms]:::action D --> H[Increase anticholinesterase or immunotherapy]:::action D --> I[Treat precipitating factors]:::action ``` ### Edrophonium (Tensilon) Test Historically used to differentiate: - **Cholinergic crisis:** Edrophonium worsens weakness (contraindicated — dangerous) - **Myasthenic crisis:** Edrophonium improves weakness temporarily **Warning:** Edrophonium test is rarely used now due to cardiac risks; clinical diagnosis and antibody titers are preferred. ### Why This Patient Has Cholinergic Crisis 1. Recent initiation of pyridostigmine without dose titration 2. Acute onset of respiratory distress + increased salivation (autonomic signs) 3. Fasciculations may be visible on examination 4. Improvement would occur after stopping the drug (diagnostic and therapeutic) [cite:Harrison 21e Ch 382]