Myasthenia gravis (MG) is a rare autoimmune disease characterized by the body’s immune system attacking components of the neuromuscular junction (NMJ). Damage to the NMJ inhibits the transmission of electrical signals from the nerve to the muscle, causing weakness of voluntary skeletal muscles and fatigue with repetitive muscle contractions. This affects the eyes, limbs, and bulbar and respiratory systems in particular.1

Life Expectancy

No cure exists for MG. Previously, the mortality rate in the 1940s and 1950s exceeded 30% of individuals diagnosed with MG; however, due to the advancement of critical care technology, improved diagnostic methods, and immunosuppressive treatments, only 3% to 4% of individuals with MG die from the condition, primarily due to thymomas or myasthenic crises, during which the respiratory system fails.1,2 

With expedient immunosuppressant treatment and careful monitoring, individuals with MG typically live full, almost normal lives.2 As many as 40% of individuals with MG achieve complete remission. While remission may be permanent in some people with MG, others may experience exacerbation of symptoms following a temporary remission.1 Between 38% and 60% of individuals with MG and concomitant thyroid hyperplasia who undergo thymectomies achieve complete stable remission, improving life expectancy as well as quality of life. 3,4 

Age of Onset

The onset of MG is typically described as early onset (≤40 years of age) or late onset (>40 years of age).4 Prognostic factors for remission include age at disease onset <40 years and disease duration <1 year from time of onset to time of diagnosis.4-6     

While MG can present at any age, the condition most commonly affects women under the age of 40 years with an estimated 3:1 sex ratio. Men become increasingly more affected after the age of 50 years, bringing the sex ratio closer to 1:1. Scientists suggest that pregnancy, childbirth, stress, and viral infections predispose women of childbearing age to MG, explaining the middle-aged sex disparities.7-9

Diagnosis of MG after 70 years of age is more difficult due to comorbid conditions providing an alternative explanation for manifesting symptoms. The difficulty of accurate diagnosis of MG in elderly patients may contribute to higher mortality rates in the elderly population, necessitating prompt diagnosis and treatment.10 

Myasthenia Gravis Type

Around 15% of patients with MG experience symptoms of ocular MG only, while the remaining 85% with ocular symptoms progress to generalized MG, usually within 1 year of disease onset. Generalized MG results in muscle weakness and fatigue in other regions of the body than the eyes. Patients with generalized MG have a greater likelihood of experiencing a life-threatening myasthenic crisis, involving failure of critical respiratory muscles, whereas those with ocular MG experience less serious symptoms such as diplopia and ptosis.6-9,11  

Prognostic factors for the conversion of ocular MG to generalized MG include thymic abnormalities and positive responses to repeated facial nerve stimulation tests. A positive response to repeated facial nerve stimulation is defined as an activity decrease of more than 10% in the nasalis or orbicularis oculi muscles, suggesting ocular MG. Treatment of ocular MG with immunosuppressants helps prevent disease progression to generalized MG.12 

References

  1. Pool JJ. The outlook for someone with myasthenia gravis. Myasthenia-Gravis.com. February 8, 2021. Accessed February 23, 2022.
  2. Juel VC, Massey JM. Myasthenia gravis. Orphanet J Rare Dis. 2007;2:44. doi:10.1186/1750-1172-2-44
  3. Wakata N, Iguchi H, Sugimoto H, Nomoto N, Kurihara T. Relapse of ocular symptoms after remission of myasthenia gravis—a comparison of relapsed and complete remission cases. Clin Neurol Neurosurg. 2003;105(2):75-77. doi:10.1016/S0303-8467(02)00104-X 
  4. Yang J, Liu C, Li T, Li C. Prognosis of thymectomy in myasthenia gravis patients with thymus hyperplasia. Int J Neurosci. 2017;127(9):785-789. doi:10.1080/00207454.2016.1257993
  5. Mao ZF, Mo XA, Qin C, Lai YR, Olde Hartman TC. Course and prognosis of myasthenia gravis: a systematic review. Eur J Neurol. 2010;17(7):913-921. doi:10.1111/j.1468-1331.2010.03017.x 
  6. Wang L, Zhang Y, He M. Clinical predictors for the prognosis of myasthenia gravis. BMC Neurol. 2017;17(1):77. doi:10.1186/s12883-017-0857-7
  7. Howard JF Jr. Clinical overview of MG. Myasthenia Gravis Foundation of America. Accessed February 23, 2022.
  8. Carr AS, Cardwell CR, McCarron PO, McConville J. A systematic review of population based epidemiological studies in myasthenia gravis. BMC Neurol. 2010;10:46. doi:10.1186/1471-2377-10-46
  9. Dresser L, Wlodarski R, Rezania K, Soliven B. Myasthenia gravis: epidemiology, pathophysiology and clinical manifestations. J Clin Med. 2021;10(11):2235. doi:10.3390/jcm10112235
  10. Hernandez Fustes OJ, Arteaga Rodriguez C, Hernandez Fustes OJ. Myasthenia gravis with elderly onset at advanced age. Cureus. 2020;12(1):e6808. doi:10.7759/cureus.6808
  11. Ocular myasthenia gravis. Brigham and Women’s Hospital. Accessed February 23, 2022.
  12. Witthayaweerasak J, Rattanalert N, Aui-Aree N. Prognostic factors for conversion to generalization in ocular myasthenia gravis. Medicine (Baltimore). 2021;100(19):e25899. doi:10.1097/MD.0000000000025899

Reviewed by Kyle Habet, MD, on 2/25/2022.

READ MORE ON