ContentsSynopsisCodesLook ForDiagnostic PearlsDifferential Diagnosis & PitfallsBest TestsManagement PearlsTherapyDrug Reaction DataReferencesView all Images (2)
Myasthenia gravis
Print
Other Resources UpToDate PubMed

Myasthenia gravis

Print Images (2)
Contributors: David Brodell MD, Richard L. Barbano MD, PhD, Lowell A. Goldsmith MD, MPH
Other Resources UpToDate PubMed

Synopsis

Myasthenia gravis (MG) is a neuromuscular autoimmune disease characterized by painless, fluctuating motor weakness of voluntary muscles. Autoimmune MG may be ocular or generalized.
  • Eye movement abnormalities cause a range of symptoms from visual blurriness to frank diplopia. Ocular symptoms including asymmetric ptosis are common and among the presenting symptoms in over half of patients.
  • In generalized MG, dysphagia, dysarthria, fatigable chewing, hypophonia, neck muscle weakness, and proximal limb weakness may be prominent in addition to ocular manifestations. Diaphragm paralysis may occur in advanced stages, leading to crisis and the need for respiratory assistance.
Muscle fatigability is a hallmark; weakness worsens with activity and improves with rest / sleep. MG typically progressively worsens and then peaks several years after the first symptom. Approximately 50% of patients who present with ocular symptoms progress to generalized MG.

Autoimmune MG is thought to involve antibodies to the acetylcholine receptor (AChR-Ab), and such antibodies are detectable in approximately 80%-85% of patients. About 40% of patients who do not have AChR-Ab will have antibodies to muscle-specific tyrosine kinase (MuSK-Ab), a receptor-associated protein. About 10% of acquired cases remain seronegative; this is more common among patients with isolated ocular myasthenia. There are also congenital and juvenile forms of the disease.

In generalized MG, females are affected more frequently than males (3:2). It is somewhat more common in women under 40 and men over 60. MG is associated with other autoimmune disorders, including thymoma, thyroid disease, Hashimoto thyroiditis, scleroderma, rheumatoid arthritis, systemic lupus erythematosus, and multiple sclerosis. Additionally, in patients with MG who become pregnant, the highest risk for exacerbation occurs in the first trimester and in the acute postpartum period.

There is no cure, but MG can be managed with anti-acetylcholinesterase medications, thymectomy, and immunosuppression. Most patients have an average life span, although exacerbations of the disease can lead to intubation and even death.

For more information, see OMIM.

Codes

ICD10CM:
G70.00 – Myasthenia gravis without (acute) exacerbation
G70.01 – Myasthenia gravis with (acute) exacerbation

SNOMEDCT:
91637004 – Myasthenia gravis

Look For

Subscription Required

Diagnostic Pearls

Subscription Required

Differential Diagnosis & Pitfalls

  • Inherited congenital myasthenic syndromes – While autoimmune MG is the predominant form, genetic mutations affecting the neuromuscular junction may be present. This diagnosis requires molecular analysis and likely genetic counseling.
  • Lambert-Eaton myasthenic syndrome (LEMS) – Proximal muscles are often affected first, and ptosis and diplopia are common. Unlike muscle changes in MG, weakness is often improved with exertion in LEMS (Lambert's sign). Also, patients may develop autonomic symptoms, reflexes are diminished, and squamous cell lung cancer is common in LEMS. Similar to MG, respiratory distress is common in advanced disease. Immunosuppression and plasmapheresis are often necessary in severe disease.
  • Thyroid ophthalmopathy
  • Kearns-Sayre syndrome
  • Myotonic dystrophy
  • Intracranial mass causing brainstem or cranial nerve pathology
  • Drug-induced MG – Common offending agents include penicillamine, aminoglycosides, quinolones, macrolides, and procainamide.
  • Botulism
  • Hyperthyroidism (Graves disease)
  • Oculopharyngeal dystrophy
  • Depression / apathy
  • Generalized fatigue

Best Tests

Subscription Required

Management Pearls

Subscription Required

Therapy

Subscription Required

Drug Reaction Data

Below is a list of drugs with literature evidence indicating an adverse association with this diagnosis. The list is continually updated through ongoing research and new medication approvals. Click on Citations to sort by number of citations or click on Medication to sort the medications alphabetically.

Subscription Required

References

Subscription Required

Last Reviewed: 05/01/2017
Last Updated: 06/12/2017
Copyright © 2019 VisualDx®. All rights reserved.
Myasthenia gravis
Print 2 Images
View all Images (2)
(with subscription)
Myasthenia gravis : Diplopia, Dysarthria, Eyelid ptosis, Recurring episodes or relapses, Dysphagia, Generalized weakness
Copyright © 2019 VisualDx®. All rights reserved.