A myasthenic crisis happens when the respiratory muscles get too weak to move enough air in and out of the lungs. The patient is unable to breathe and a machine (ventilator) is needed to help breathe for the patient. The ventilator may do this through a tube into the airway (endotracheal intubation) or a tight-fitting mask on the face (Bi-PAP). Myasthenic crisis involves only the respiratory muscles so it is different from an MG flare (exacerbation). An MG flare is the worsening of some or all muscles throughout the body, not just the muscles used for breathing. MG flares vary from patient to patient but may include worsened double vision, increased arm weakness, falling, unsteady walking, or having a hard time swallowing. Many muscles throughout the body may weaken during an MG exacerbation but myasthenic crisis refers specifically to severe, life-threatening weakness of respiratory muscles. Certain issues are known to trigger (cause) myasthenic crises. (see page 2, Conditions …Trigger Weakness) Myasthenic crises can develop slowly or quickly. It is important for patients to get medical care right away when symptoms of myasthenic crisis develop.

A patient may be admitted to the hospital with a diagnosis of myasthenic crisis even though a ventilator is not needed yet. This is because aggressive treatment is needed in order to prevent a full myasthenic crisis and to keep the patient breathing without a machine.