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What Is a Myasthenic Crisis?

Reviewed by: HU Medical Review Board | Last reviewed: August 2020

The most serious complication of myasthenia gravis (MG) is called a myasthenic crisis. A myasthenic crisis happens when a person with MG has so much trouble breathing that they need medical help.1,2

Myasthenic crisis is not a common symptom, but it does happen to about 1 in 5 people with MG at least once.1,2

What is a myasthenic crisis?

There are myasthenic flares and myasthenic crises. A flare is different from person to person, but it generally happens when some or all of the muscles involved in MG get more weak. This may cause worse double vision, falling, unsteady walking, or more problems swallowing.2

A myasthenic crisis results in weakness of the breathing (respiratory) muscles. It is a potentially life-threatening situation that requires emergency care. A crisis usually develops after days or weeks of slowly worsening symptoms.2

What are the causes?

About half of all people who have a myasthenic crisis can find no obvious cause for the crisis. However, there are some common things that can trigger a crisis, including:2,3

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  • Illness or infection
  • Pregnancy or childbirth
  • Extreme temperatures
  • Stress, especially from surgery or trauma
  • Lack of sleep
  • Magnesium (especially if given by IV)
  • Some antibiotics
  • Certain high blood pressure and heart drugs
  • Some anesthesia and paralytics (neuromuscular blocking agents)
  • Botox (botulinum toxin)

Stopping your regular MG medicines without talking to your doctor or taking smaller doses than prescribed can also trigger muscle weakness. In some cases, you may be taking a drug for another health condition that can make your MG symptoms worse. That is why it is important to talk with your doctor about all of the prescription and over-the-counter drugs, vitamins, and other supplements you are taking.

What are the signs?

Despite the word “crisis” being in the name, a myasthenic crisis does not always come on quickly. The shortness of breath or trouble breathing usually builds up over days. And, some people with myasthenia gravis may feel short of breath because of anxiety, lung disease, or heart problems. That is why it is important to recognize the early signs and get help as quickly as possible.

A myasthenic crisis may be developing if you feel short of breath and you:2

  • Have a hard time lying flat in bed without feeling short of breath
  • Are breathing very quickly (more than 25 breaths per minute)
  • Pause in the middle of what you are saying to take a breath
  • Have more slurred speech
  • Have a weak cough or have trouble clearing mucus or saliva from your throat
  • Have a harder than normal time chewing and swallowing
  • Have trouble holding your neck up
  • Feel much more weakness than normal in your arms or legs, plus are short of breath
  • See the muscles between your ribs, neck, and stomach pull in during a breath
  • Cannot count out loud past 20 after taking a breath

If you feel short of breath and also have any of the above symptoms, call your doctor or 911 right away.

Using a pulse oximeter at home

A machine called a pulse oximeter measures the amount of oxygen in the blood. This measurement can tell your doctor whether you are breathing well enough to supply the oxygen your body needs.

You can buy a small pulse oximeter to keep at home to monitor your blood oxygen levels. However, you should talk to your doctor about how to use this machine correctly and what its test results mean for your care.

How to prepare

It can be helpful to prepare a few things ahead of time just in case you have a myasthenic crisis. First, keep an updated packet of information with your important health details, such as:2

  • Contact information for your neurologist and other doctors
  • List of all your current drugs and supplements
  • Health insurance information
  • Information about any IV ports, pacemakers, and other implanted devices
  • Your emergency contacts (friends or family)
  • A list of drugs that can be dangerous to people with MG
  • Your medical history and hospital records

Your local 911 call center may have a special database you can register with so that emergency services can help you even if you cannot speak during a myasthenic crisis.