The Essential Guide

What are the symptoms of MG?

The first major symptom of myasthenia gravis is fatiguability. Muscles progressively become weaker and weaker during active periods and then improve during periods of rest. The most susceptible muscles are those controlling eye movement, facial expressions, chewing, talking and swallowing. But also, muscles which control limb movement and A photograph of someone suffering from neck muscle weakness/pain characteristic of MGbreathing can be affected.

Onset of MG can be sudden with intermittent symptoms. These symptoms can highly variable and subtle. Weakness of eye muscles is usually the first, obvious symptom. Sometimes the first, noticeable symptom can be slurred speech of difficulty with swallowing.

The symptoms which vary the most in severity include ptosis (eyelid drooping), diplopia (double vision), unstable gait, weakness of arms, hands, fingers, toes and neck, dysphagia (difficulty with swallowing), dysarthria (speech impediment) and shortness of breath. Ptosis and diplopia are the major symptoms of ocular myasthenia (when MG is limited to the muscles of the eye only).An example of ptosis of the left eye

Ptosis, as seen in the photo, is a condition which causes drooping of one or both eyes. This is caused when the border of the upper eyelid falls to a lower position than normal. When this condition is severe, the eyelid can interfere with vision as it may cover all or part of the pupil. Ptosis can occur as an isolated condition or it can be indicator of a more serious, underlying problem which is affecting the muscles. In generalized myasthenia gravis, ptosis is often the first noticeable symptom.

Diplopia can also occur as a result of MG and is commonly described as being the simultaneous perception of a single object as a double image. Diplopia can be monocular (in one eye), binocular (in two eyes) or temporary (as a result of alcohol intoxication or concussion).

Classifications of MG

There are 5 different classifications of myasthenia gravis, which increase with severity.

Class 1:

  •  any weakness of the eye muscles, ptosis, no other muscle weakness elsewhere

Class 2:

  • weakness of the eye muscles (any severity)
  • mild weakness of other muscles
  • Class 2a: weakness of the limbs or axial muscles
  • Class 2b: weakness of respiratory muscles and/or bulbar muscles

Class 3:

  • weakness of the eye muscles (any severity)
  • mild to moderate weakness of other muscles
  • Class 3a: weakness of limb or axial muscles
  • Class 3b: weakness of respiratory muscles and/or bulbar muscles

 Class 4:

  • weakness of the eye muscles (any severity)
  • severe weakness of other muscles
  • Class 4a: weakness of limb or axial muscles
  • Class 4b: weakness of respiratory muscles and/or bulbar muscles

 Class 5:

  • same symptoms as Class 4
  • additionally requires intubation in order to maintain airway

Myasthenia Crisis (MC)


Myasthenic crisis is a life-threatening, acute episode of muscle weakness that can occur as a result of MG and is a result of a severe lack of acetylcholine. This condition is serious enough for the patient to require intubation, as a result of failure of the respiratory system. It can affect 15 to 30% of patients suffering from MG.

The respiratory muscles become paralysed and severe weakness of the oropharyngeal muscles can also occur. When the upper airways become obstructed it is necessary for the patient to be intubated. Mechanical ventilation can sometimes be required. Immediate treatment with a combination of corticosteroids and either immunoglobulin or plasma exchange is required.


What can cause MC?


A variety of factors can cause myasthenic crisis. The most common of these is a recurring infection, such as pneumonia. Myasthenic crisis can also occur following surgery, childbirth, during pregnancy or while undergoing immunosuppressant treatment. It can also occur as a result of myasthenia gravis itself. Particular antibiotics (such as erythromycin and azithromycin), cardiac drugs (beta-blockers, procainamide and quinidine) and also magnesium have been known to increase the muscle weakness occurring in MG, thus increasing the risk of MC.

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