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Myasthenia gravis

Myasthenia gravis
Eye deviation and a drooping eyelid in a person with myasthenia gravis trying to open her eyes
SpecialtyNeurology
SymptomsVarying degrees muscle weakness, double vision, drooping eyelids, trouble talking, trouble walking[1]
Usual onsetWomen under 40, men over 60[1]
DurationLong term[1]
CausesAutoimmune disease[1]
Diagnostic methodBlood tests for specific antibodies, edrophonium test, nerve conduction studies[1]
Differential diagnosisGuillain–Barré syndrome, botulism, organophosphate poisoning, brainstem stroke,[2] metabolic myopathies
TreatmentMedications, surgical removal of the thymus, plasmapheresis[1]
MedicationAcetylcholinesterase inhibitors (neostigmine, pyridostigmine), immunosuppressants[1]
Frequency50 to 200 per million[3][4]

Myasthenia gravis (MG) is a long-term neuromuscular junction disease that leads to varying degrees of skeletal muscle weakness.[1] The most commonly affected muscles are those of the eyes, face, and swallowing.[1][5] It can result in double vision, drooping eyelids, and difficulties in talking and walking.[1] Onset can be sudden.[1] Those affected often have a large thymus or develop a thymoma.[1]

Myasthenia gravis is an autoimmune disease of the neuro-muscular junction which results from antibodies that block or destroy nicotinic acetylcholine receptors (AChR) at the junction between the nerve and muscle.[6][7][1] This prevents nerve impulses from triggering muscle contractions.[1] Most cases are due to immunoglobulin G1 (IgG1) and IgG3 antibodies that attack AChR in the postsynaptic membrane, causing complement-mediated damage and muscle weakness.[8] Rarely, an inherited genetic defect in the neuromuscular junction results in a similar condition known as congenital myasthenia.[9][10] Babies of mothers with myasthenia may have symptoms during their first few months of life, known as neonatal myasthenia.[1] Diagnosis can be supported by blood tests for specific antibodies, the edrophonium test, electromyography (EMG), or a nerve conduction study.[1]

MG is generally treated with medications known as acetylcholinesterase inhibitors, such as neostigmine and pyridostigmine.[1] Immunosuppressants, such as prednisone or azathioprine, may also be used.[1] The surgical removal of the thymus may improve symptoms in certain cases.[1] Plasmapheresis and high-dose intravenous immunoglobulin may be used during sudden flares of the condition.[1] If the breathing muscles become significantly weak, mechanical ventilation may be required.[1] Once intubated acetylcholinesterase inhibitors may be temporarily held to reduce airway secretions.[11]

MG affects 50 to 200 people per million.[3][4] It is newly diagnosed in 3 to 30 people per million each year.[12] Diagnosis has become more common due to increased awareness.[12] MG most commonly occurs in women under the age of 40 and in men over the age of 60.[1][5][13] It is uncommon in children.[1] With treatment, most live to an average life expectancy.[1] The word is from the Greek mys, "muscle" and astheneia "weakness", and the Latin gravis, "serious".[14]

  1. ^ a b c d e f g h i j k l m n o p q r s t u v w x "Myasthenia Gravis Fact Sheet". National Institute of Neurological Disorders and Stroke.
  2. ^ Kahan S (2005). In a Page: Neurology. Lippincott Williams & Wilkins. p. 118. ISBN 978-1-4051-0432-6. Archived from the original on 8 September 2017.
  3. ^ a b Kaminski HJ (2009). Myasthenia Gravis and Related Disorders (2 ed.). Springer Science & Business Media. p. 72. ISBN 978-1-59745-156-7. Archived from the original on 8 September 2017.
  4. ^ a b Adams JG (2012). Emergency Medicine: Clinical Essentials (2 ed.). Elsevier Health Sciences. p. 844. ISBN 978-1-4557-3394-1. Archived from the original on 8 September 2017.
  5. ^ a b Salari N, Fatahi B, Bartina Y, Kazeminia M, Fatahian R, Mohammadi P, et al. (December 2021). "Global prevalence of myasthenia gravis and the effectiveness of common drugs in its treatment: a systematic review and meta-analysis". Journal of Translational Medicine. 19 (1): 516. doi:10.1186/s12967-021-03185-7. PMC 8686543. PMID 34930325.
  6. ^ Young C, McGill SC (April 2021). Rituximab for the Treatment of Myasthenia Gravis: A 2021 Update [Internet] (Report). Ottawa (ON): Canadian Agency for Drugs and Technologies in Health. PMID 34255447.
  7. ^ Dabi A, Solieman N, Kurukumbi M, Kalyanam J (2012). "Myasthenia Gravis: A Review". Autoimmune Diseases. 2012: 1–10. doi:10.1155/2012/874680. PMC 3501798. PMID 23193443.
  8. ^ Phillips WD, Vincent A (1 January 2016). "Pathogenesis of myasthenia gravis: update on disease types, models, and mechanisms". F1000Research. 5: 1513. doi:10.12688/f1000research.8206.1. PMC 4926737. PMID 27408701.
  9. ^ Kandel E, Schwartz J, Jessel T, Siegelbaum S, Hudspeth A (2012). Principles of Neural Science (5 ed.). pp. 318–319.
  10. ^ Vrinten C, van der Zwaag AM, Weinreich SS, Scholten RJ, Verschuuren JJ (December 2014). "Ephedrine for myasthenia gravis, neonatal myasthenia and the congenital myasthenic syndromes". The Cochrane Database of Systematic Reviews. 2014 (12): CD010028. doi:10.1002/14651858.CD010028.pub2. PMC 7387729. PMID 25515947.
  11. ^ Godoy DA, Mello LJ, Masotti L, Di Napoli M (September 2013). "The myasthenic patient in crisis: an update of the management in Neurointensive Care Unit". Arquivos de Neuro-Psiquiatria. 71 (9A): 627–39. doi:10.1590/0004-282X20130108. PMID 24141444.
  12. ^ a b McGrogan A, Sneddon S, de Vries CS (2010). "The incidence of myasthenia gravis: a systematic literature review". Neuroepidemiology. 34 (3): 171–183. doi:10.1159/000279334. PMID 20130418. S2CID 34447321.
  13. ^ Conti-Fine BM, Milani M, Kaminski HJ (November 2006). "Myasthenia gravis: past, present, and future". The Journal of Clinical Investigation. 116 (11): 2843–2854. doi:10.1172/JCI29894. PMC 1626141. PMID 17080188.
  14. ^ Ehrlich A, Schroeder CL (2014). Introduction to Medical Terminology. Cengage Learning. p. 87. ISBN 978-1-133-95174-2. Archived from the original on 8 September 2017.