Myasthenia gravis

Myasthenia gravis (MG) is the most common neuromuscular junction disease and presents with weakness worsened by exertion but improving with rest.


Incidence is estimated at 15-20 per 100,000 . Females are more affected (3:1) under the age of 40, but males are more affected by the age of 50 .


Clinical presentation

The classic feature of myasthenia gravis is fluctuating weakness that is fatiguable, worsening with activity and improving with rest . Two-thirds of patients present with ocular symptoms (e.g. diplopia, ptosis), with the majority (80%) proceeding to experience generalized weakness .


Myasthenia gravis is an autoimmune disease. The disease can be associated with several antibodies. These include:

  • AChR Ab: antibodies affecting postsynaptic acetylcholine receptors
  • MuSK Ab: antibodies affecting muscle specific kinase 
  • titin Ab
  • RyR Ab

Treatment and prognosis

Symptomatic treatment with cholinesterase inhibitors (e.g. pyridostigmine) are first line treatment in myasthenia gravis. Severe cases usually require plasmapharesis or immunoglobulin therapy. Corticosteroids and immunosuppressive drugs (e.g. cyclosporin, cyclophosphamide, azathioprine and mycophenolate mofetil) are used for immunomodulation in the chronic setting of the disease . Thymectomy for patients with a thymoma is usually recommended .

Patients with myasthenia gravis can present with a sudden worsening of symptoms termed a myasthenic crisis which can compromise the respiratory muscles in some cases. This can be precipitated by concurrent infection or medication use (e.g. aminoglycosides) .

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