Neuro ICU > Myasthenia Gravis
Myasthenia Gravis (MG)
What is it?
MG is a chronic autoimmune disease that affects the acetylcholine receptors at neuromuscular junctions of voluntary skeletal muscles, causing weakness that worsens after periods of activity and improves with rest. Muscles affected generally control eye and eyelid movement, facial expression, chewing, talking, and swallowing. Exacerbations and myasthenic crisis can be triggered by exercise, heat or warmth, anxietyacute or impending illness, infection, menstruation, pregnancy/postpartum, missed medications, major surgery, certain antibiotics, and cardiac medications.
Onset
Can be sudden, and the severity of weakness varies. Women are more affected with an earlier onset (20-30 years old), whereas men are more affected with a later onset (60-80 years old).
How is it diagnosed?
Diagnosed using a few different tests. Since weakness is a common symptom of many different disorders, diagnosis may be delayed or missed
Physical and neurological exam: assess strength, tone, sensation, coordination, and eye movements
Edrophonium test: injection of edrophonium chloride can briefly relieve weakness in people with myasthenia gravis
Blood test: to look for elevated levels of acetylcholine receptor antibodies or the presence of the anti-MuSK antibody
Electrodiagnostics: repetitive nerve stimulation. Typically, in MG, the muscle fibers do not respond well to repeated electrical stimulation.
Diagnostic imaging: CT or MRI may identify the presence of a thymoma.
Pulmonary function testing: to measure breathing strength
Symptoms
The hallmark symptom is that weakness is worse after activity but improves with rest. General symptoms include:
Ocular myasthenia
Ptosis
Diplopia
Change in facial expression
Difficulty swallowing
Shortness of breath
Dysarthria
Weakness of the arms, legs, and neck
Myasthenic Crisis
A myasthenic crisis is a severe exacerbation of MG leading to respiratory failure — the primary reason MG patients are admitted to the ICU. It occurs when weakness of the respiratory and/or pharyngeal muscles becomes life-threatening.
Common triggers:
- Infection (most common)
- Surgical stress or anesthesia
- Missed medications
- Certain medications (e.g., aminoglycosides, beta-blockers, fluoroquinolones)
- Emotional stress, pregnancy, or postpartum
Warning signs to watch for during therapy:
- Rapidly worsening weakness during or after activity
- Increasing ptosis or diplopia
- Worsening dysarthria or dysphagia
- Shortness of breath or declining SpO₂
ICU management:
Ventilatory support (often BiPAP before intubation), plasmapheresis, and IVIG. Defer therapy during active myasthenic crisis. Resume only when the patient is stabilized and the medical team has cleared activity.
Osserman and Genkins Classification (MG Staging)
(Osserman & Genkins, 1971; Hamby, 2024)
| Stage | Description | ICU Relevance |
|---|---|---|
| Stage 1 | Ocular signs only (ptosis, diplopia) | Rarely requires ICU admission |
| Stage 2A | Mild generalized weakness — limbs and/or trunk (with or without ocular) | May present during initial hospitalization or exacerbation |
| Stage 2B | Mild oropharyngeal and/or respiratory muscle weakness; limbs and trunk may also be affected | Bulbar involvement begins — SLP consultation critical |
| Stage 3 | Moderate generalized weakness and/or bulbar dysfunction; ocular signs may also be present (3A: limbs/trunk primary; 3B: oropharyngeal/respiratory primary) | High aspiration and respiratory compromise risk |
| Stage 4 | Acute, sudden, and severe presentation; respiratory dysfunction. 4B requires a feeding tube without intubation | ICU-level care typically required; energy conservation essential |
| Stage 5 | Intubation with or without mechanical ventilation — myasthenic crisis | Defer therapy until extubated and medically stable |
Prognosis
Most individuals can significantly improve their muscle weakness and lead normal or nearly normal lives. Some cases may go into remission (temporary or permanent). Long-lasting remission is the goal of thymectomy and can occur in 50% of individuals.
Treatment
Focused on reducing muscle weakness and improving functional strength
Thymectomy: The thymus gland is often impaired in individuals with MG. Surgical removal can reduce symptoms and often cure the individual.
Monoclonal antibody: Targets the process by which acetylcholine antibodies injure the neuromuscular junction.
Anticholinesterase medications: Slow the breakdown of acetylcholine at the neuromuscular junction. This can improve neuromuscular transmission and increase strength.
Immunosuppressive drugs: Suppress the production of abnormal antibodies, reducing the autoimmune attack on the neuromuscular junction.
Plasmapheresis: blood cleansing procedure in which the plasma antibodies are removed and replaced with albumin or fresh frozen plasma.
Intravenous immunoglobulin (IVIG): high-dose plasma protein replacement therapy in which the patient receives intravenous injections of immunoglobulins. This is thought to lower the levels or overall effectiveness of the antibodies that are attacking the nerves.
Therapy Implications
Energy conservation is the cornerstone of MG therapy. Weakness worsens predictably with activity — overactivity, heat, fever, and stress can exacerbate weakness and fatigue. Rest alleviates weakness and fatigue. Plan sessions around this principle, not against it.
Time sessions strategically: Schedule earlier in the day before fatigue accumulates. Multiple brief sessions are preferable to one prolonged session. Build rest breaks into every session — do not wait for the patient to report fatigue before incorporating them.
Visual symptoms require specific accommodations:
Avoid tasks requiring sustained upward gaze — this can worsen ptosis
If diplopia is present, consider patching or partial occlusion; teach the patient strategies so they can adjust as symptoms change
If the eye will not close, it must be manually closed — tape it closed with gauze until the physician addresses it
Falls risk is elevated due to diplopia — assess carefully before any mobility
Bulbar and swallowing involvement: Dysphagia is present with pharyngeal, palatal, and tongue muscle weakness. The patient fatigues quickly while chewing. Ensure SLP is involved. Be aware of high risk for malnutrition and dehydration. If the mouth stays open, the patient may have to manually keep it closed.
Respiratory monitoring: Acute respiratory failure is the highest risk. Avoid fatigue or overactivity because it can lead to increased dyspnea and fatigue of respiratory musculature. Report vitals in documentation — this information may be important in determining medication dosage or for warning of an impending crisis.
Immobility complications are high risk: DVT and pressure injuries are significant concerns. Factor in mobility limitations and immobility risk when planning sessions — even brief, low-intensity upright activity may be beneficial if the patient can tolerate it.
After plasmapheresis: The patient may have hypotension and dizziness. Be cautious with functional mobility following treatment — check BP before and after position changes.
Monitor for the warning signs of myasthenic crisis (see callout above) throughout the session. Stop and notify nursing immediately if rapidly worsening weakness, increasing ptosis, worsening speech or swallowing, or declining SpO₂ are observed.
Prioritize high-value functional tasks: ADL performance, communication, and positioning. Adaptive equipment (built-up handles, lightweight utensils, environmental modifications) can significantly reduce energy expenditure — assess early.
References
Hamby, J. R. (2024). The nervous system, part 2: Neurodegenerative diseases and other conditions. In H. Smith-Gabai & S. E. Holm (Eds.), Occupational Therapy in Acute Care (3rd ed., pp. 449–496). AOTA Press.
National Institute of Neurological Disorders and Stroke. (2021, November 15). Myasthenia Gravis Fact Sheet. https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Myasthenia-Gravis-Fact-Sheet