At the neuromuscular junction, the nerve ending releases acetylcholine (ACh), which binds to ACh receptors on the muscle to trigger contraction. The enzyme acetylcholinesterase then breaks ACh down.

Myasthenia gravis (MG)

• An autoimmune disease: antibodies block or destroy postsynaptic ACh receptors (anti-AChR antibodies in most clients; anti-MuSK or anti-LRP4 in some).
• With repeated use, less ACh binding occurs, so muscles fatigue with activity and recover with rest.
• The thymus is abnormal in many clients (hyperplasia or thymoma).
• Peaks in women in their 20s–30s and men over 50. It is not hereditary in the usual sense.
• Types: ocular MG (eye muscles only) and generalized MG (limbs, bulbar, and respiratory muscles).

Lambert-Eaton myasthenic syndrome (LEMS)

• Antibodies against presynaptic voltage-gated calcium channels reduce ACh release.
• Often paraneoplastic, especially with small cell lung cancer.
• Features that differ from MG: proximal leg weakness, strength briefly improves with repeated effort, reduced reflexes, and autonomic symptoms — dry mouth, constipation, erectile dysfunction, orthostatic hypotension.

Comparison with Guillain-Barré syndrome (GBS) — covered fully in Topic 70

• Ptosis (drooping eyelid) and diplopia (double vision) — the most common first symptoms.
• Weakness that worsens with activity and toward the end of the day, improving after rest.
• Bulbar weakness: dysphagia, choking, nasal voice, dysarthria, fatigue while chewing, weak facial expression ("snarl" smile).
• Proximal limb and neck weakness.
• Respiratory weakness: shallow breathing, dyspnea, weak cough, inability to count to 20 in one breath, use of accessory muscles, orthopnea.
• Sensation and reflexes are normal.

Myasthenic crisis — severe weakness of respiratory and/or bulbar muscles needing ventilation or airway protection. Triggers: infection (most common), surgery, stress, pregnancy, tapering immunotherapy, starting high-dose corticosteroids, and drugs that impair neuromuscular transmission.

Cholinergic crisis — excess acetylcholinesterase inhibitor. Also causes weakness and respiratory failure, but with muscarinic signs: excessive salivation and bronchial secretions, sweating, abdominal cramps, diarrhea, bradycardia, small pupils, and fasciculations. It is uncommon at usual doses.

Respiratory monitoring: forced vital capacity (FVC) and negative inspiratory force (NIF). A common rule: intubation is considered when FVC falls below about 15–20 mL/kg or NIF is weaker than about −20 to −30 cm H₂O. SpO₂ and ABGs change late — do not rely on them.

The edrophonium (Tensilon) test is now rarely used and the drug is unavailable in many countries; atropine had to be ready because of bradycardia.

Rapid therapies for crisis or before surgery

• Plasmapheresis (plasma exchange) — removes antibodies; works within days. Complications: hypotension, bleeding tendency (loss of clotting factors), hypocalcemia from citrate (perioral tingling, cramps), infection and thrombosis at the central line, fluid shifts.
• IV immunoglobulin (IVIG) — headache, aseptic meningitis, thrombosis, acute kidney injury, anaphylaxis in IgA deficiency; infuse slowly, hydrate.

Myasthenic crisis management: ICU, airway protection with intubation or noninvasive ventilation, plasmapheresis or IVIG, treat the trigger (infection). Acetylcholinesterase inhibitors are often held while the client is ventilated to reduce secretions.

Cholinergic crisis management: hold the acetylcholinesterase inhibitor, support ventilation, suction secretions, and give atropine as ordered — keep atropine at the bedside. In both crises the first action is airway and breathing support.

Drugs that can worsen MG — avoid or use with close monitoring

• Aminoglycosides (gentamicin, tobramycin), fluoroquinolones (boxed warning), macrolides (azithromycin), telithromycin
• Magnesium (IV magnesium sulfate)
• Beta blockers, some calcium channel blockers, procainamide, quinine
• Neuromuscular blocking agents — anesthesia must be planned
• Botulinum toxin; immune checkpoint inhibitors; D-penicillamine; statins in some clients; iodinated contrast (rare)

LEMS treatment: find and treat the cancer; amifampridine increases ACh release (risk of seizures — contraindicated with seizure history; perioral tingling); immunotherapy.

Listed in priority order.

1. Airway and breathing — the top priority
   • For sudden dyspnea or dysphagia: assess airway and breathing, position upright, give oxygen as needed, suction secretions, and call for help; prepare for intubation.
   • Serial FVC and NIF as ordered; report decline promptly. Watch for weak cough, inability to handle secretions, rising respiratory rate, and paradoxical breathing.
   • Keep suction and a bag-valve mask at the bedside.
2. Aspiration prevention
   • Time meals for peak medication effect; upright position; soft foods, small bites, rest between bites; thickened liquids if ordered; stop feeding if choking occurs.
3. Medication safety
   • Give pyridostigmine exactly on time; check timing when the client is NPO (may need an alternative route).
   • Screen new prescriptions for drugs that worsen MG; alert the prescriber and pharmacist.
   • Distinguish worsening MG from cholinergic excess (secretions, cramps, bradycardia) and report.
4. After thymectomy (often through a median sternotomy or minimally invasive chest approach)
   • Monitor breath sounds, respiratory pattern, and chest tube — watch for pneumothorax and respiratory insufficiency; pain control to allow deep breathing; resume anticholinesterase medications as ordered.
5. After plasmapheresis
   • Monitor BP (hypotension), bleeding, signs of hypocalcemia, and the central line site.
6. Energy conservation and eye protection
   • Schedule activities during peak strength; rest periods.
   • Ptosis and incomplete eye closure: eye patch alternating eyes for diplopia, lubricating drops, tape eyelids at night if ordered.
7. Communication — alternative methods when speech tires.

• MG is chronic; the primary goal is to maintain breathing and swallowing and prevent crisis.
• Take pyridostigmine on schedule, 30–60 minutes before meals; never adjust doses on your own.
• Never stop corticosteroids abruptly; take with food; monitor glucose and BP.
• Report early signs of infection (fever, cough, urinary symptoms) and seek care promptly — infection is the most common trigger of crisis. Get recommended vaccines (inactivated vaccines; live vaccines are avoided during immunosuppression).
• Seek emergency care for trouble breathing, swallowing, or speaking, or for weak cough.
• Tell every provider, dentist, and pharmacist you have MG; carry a medical alert card listing drugs to avoid.
• Avoid extreme heat, emotional stress, fatigue, and alcohol, which can worsen weakness.
• Women planning pregnancy should discuss medications first (some immunosuppressants are teratogenic); symptoms can change during pregnancy and after delivery.

• MG = autoimmune attack on postsynaptic ACh receptors; weakness worse with activity and in the evening, better with rest.
• First signs: ptosis and diplopia; normal sensation and reflexes.
• Priority = airway and breathing; monitor FVC and NIF (SpO₂ changes late).
• Pyridostigmine: 30–60 minutes before meals, strict schedule; muscarinic side effects.
• Myasthenic crisis (too little effect, infection trigger) vs cholinergic crisis (too much drug, secretions, cramps → hold drug, give atropine).
• Crisis treatment: ventilation support + plasmapheresis or IVIG.
• Plasmapheresis → hypotension, bleeding tendency, hypocalcemia.
• Avoid aminoglycosides, fluoroquinolones, magnesium, neuromuscular blockers.
• Corticosteroids can worsen MG when started; never stop abruptly.
• Thymectomy → watch for pneumothorax and respiratory status.
• LEMS: presynaptic calcium channels, small cell lung cancer, improves with repeated effort, dry mouth, orthostatic hypotension.
• Report infections early — the most common trigger of crisis.