Difference Between Myasthenia Gravis and Cholinergic Crisis

Myasthenia gravis (MG) is a chronic autoimmune disorder that causes weakness in the skeletal muscles. While it is a manageable condition for many, it can occasionally lead to two serious complications — myasthenic crisis and cholinergic crisis. These crises can both present with severe muscle weakness and respiratory distress, making them difficult to distinguish. However, their causes, symptoms, and treatments are very different, and accurate diagnosis is crucial for effective management.

This blog breaks down the key differences between myasthenic and cholinergic crises in a simple, easy-to-understand format to help patients, caregivers, and healthcare students better understand these critical conditions.

What is Myasthenia Gravis (MG)?

Myasthenia gravis is a neuromuscular disease that occurs when the immune system attacks the communication between nerves and muscles. It affects acetylcholine receptors at the neuromuscular junction, making it hard for the muscles to receive signals from the brain. This results in muscle weakness, especially in the eyes, face, throat, and limbs.

Common Symptoms of MG:

• Drooping eyelids (ptosis)
• Double vision (diplopia)
• Difficulty swallowing or speaking
• Weakness in arms and legs
• Fatigue that worsens with activity

What is a Myasthenic Crisis?

A myasthenic crisis is a life-threatening condition where the muscles that control breathing become too weak to function. This leads to respiratory failure and often requires hospitalization and ventilator support.

Causes of Myasthenic Crisis:

• Infection (most common trigger)
• Stress or surgery
• Stopping MG medications abruptly
• Underdosing or ineffective cholinesterase inhibitors
• Certain medications that worsen MG (like some antibiotics)
  

Symptoms of Myasthenic Crisis:

• Severe muscle weakness
• Difficulty breathing (shortness of breath)
• Trouble speaking or swallowing
• Weak cough or gag reflex
• Drooling due to inability to swallow

What is a Cholinergic Crisis?

A cholinergic crisis is also a medical emergency but occurs due to too much acetylcholine in the body, usually from overmedication with cholinesterase inhibitors — the drugs used to treat MG. This leads to overstimulation of the muscles and other organs, eventually causing them to become fatigued and non-functional.

Causes of Cholinergic Crisis:

• Overdose of cholinesterase inhibitors
• Accidental double-dosing
• Too frequent medication intake
• Drug interactions

Symptoms of Cholinergic Crisis:

• Muscle weakness (similar to myasthenic crisis)
• Muscle twitching or fasciculations
• Excessive salivation and tearing
• Diarrhea
• Urinary incontinence
• Nausea and vomiting
• Slow heart rate (bradycardia)
• Constriction of pupils (miosis)
• Sweating

How Can You Tell the Difference When Symptoms Look So Similar?

Both crises present with muscle weakness and difficulty breathing, which can be confusing even for medical professionals. However, other symptoms and the history of medication use can provide important clues.

Feature	Myasthenic Crisis	Cholinergic Crisis
Cause	Not enough acetylcholine due to disease or underdosing	Too much acetylcholine due to overmedication
Breathing Problems	Yes	Yes
Muscle Weakness	Yes	Yes
Excess Saliva/Diarrhea	No	Yes
Heart Rate	Normal or elevated	Often slowed
Pupil Size	Normal	Constricted

Can the Edrophonium (Tensilon) Test Help Identify the Type of Crisis?

One of the most useful tests to distinguish between the two crises is the Edrophonium test, also called the Tensilon test.

How it works:

• Edrophonium is a short-acting drug that inhibits the breakdown of acetylcholine, temporarily increasing its levels in the body.

Test Results Interpretation:

• Myasthenic Crisis: Muscle strength improves after edrophonium is given. This confirms that the crisis is due to a shortage of acetylcholine.
• Cholinergic Crisis: Muscle weakness worsens after the drug is given, confirming there is already too much acetylcholine in the system.

How Are These Crises Treated?

Since the underlying causes are different, treatment approaches are also very different.

Treatment of Myasthenic Crisis:

1. Stop medications that may be worsening the condition.
2. Respiratory support with a ventilator, if needed.
3. Plasma exchange (plasmapheresis) or intravenous immunoglobulin (IVIG) to reduce the immune system’s attack on acetylcholine receptors.
4. Restart or adjust cholinesterase inhibitors once the patient is stable.
5. Treat the underlying cause, such as infection.
   

Treatment of Cholinergic Crisis:

1. Immediately stop cholinesterase inhibitors.
2. Provide respiratory support, if needed.
3. Monitor heart rate, blood pressure, and fluid loss from diarrhea or vomiting.

How Can Crisis Be Prevented in Myasthenia Gravis?

Prevention is key to avoiding these dangerous situations. Here’s how patients and caregivers can help reduce the risk of both types of crises:

Tips to Prevent Myasthenic Crisis:

• Take medications exactly as prescribed.
• Avoid known MG triggers, including stress, certain medications, and infections.
• Get vaccinated to prevent respiratory infections.
• Visit your doctor regularly for dosage adjustments and monitoring.

Tips to Prevent Cholinergic Crisis:

• Never self-adjust medication dosage.
• Keep a medication schedule to avoid double-dosing.
• Know the early warning signs of overdose (diarrhea, salivation, sweating).
• Always inform your doctor of any other medications or supplements you’re taking.

What Should You Do in an Emergency?

If someone with MG experiences difficulty breathing, speaking, or swallowing, it could be a sign of a crisis. Call emergency services immediately. Do not attempt to diagnose or treat the condition at home.

In the ER, make sure to inform the healthcare team that the patient has myasthenia gravis and provide details about their medications and recent symptoms. Quick and accurate information can help doctors determine the right treatment quickly.

How Can You Stay Informed and Empowered While Living With Myasthenia Gravis?

Living with MG can be challenging, but with education, medical support, and awareness, it is possible to lead a full and active life. Understanding the differences between myasthenic crisis and cholinergic crisis empowers patients and caregivers to respond quickly and effectively in emergencies.

The more you know, the better prepared you are to manage MG safely and confidently.

Conclusion

While myasthenic crisis and cholinergic crisis may appear similar on the surface, they are very different in cause, effect, and treatment. One results from too little acetylcholine, while the other stems from too much. Recognizing the key differences, such as the edrophonium test response and the presence of symptoms like diarrhea or bradycardia, can help guide the right treatment path.

In any suspected crisis, immediate medical attention is essential. With the right care and knowledge, patients with myasthenia gravis can manage these complications and continue to live fulfilling lives.