Myasthenia Gravis: Recurrence, Treatment, and Life Expectancy - Rare Disease

Dr. Chen Shunsheng reply Rare Disease

---

Myasthenia Gravis Introduction: Over 95% of cases of Myasthenia Gravis (MG) are classified as autoimmune diseases.
In simple terms, this condition arises when T lymphocytes in the body fail to recognize the acetylcholine receptors (ACh receptors) at the neuromuscular junction, leading to the production of a large amount of receptor antibodies (Anti-ACh R antibodies) through immune mechanisms.
These antibodies damage the post-synaptic acetylcholine receptors at the neuromuscular junction, resulting in muscle fatigue and weakness, particularly affecting the ocular muscles, swallowing muscles, respiratory muscles, and limb muscles.
In summary, the primary pathogenic mechanism of Myasthenia Gravis is believed to be the Anti-ACh receptor antibodies that destroy the acetylcholine receptors in the post-synaptic cleft of skeletal muscle (striated muscle), leading to muscle fatigue and weakness.
The presence of these antibodies is associated with thymoma or thymic lymphoid hyperplasia, which is why approximately one-third of patients with Myasthenia Gravis have thymomas, and half have thymic lymphoid hyperplasia and enlargement.

The muscles most susceptible to involvement are the ocular muscles, which are often the first to be affected, leading to symptoms such as ptosis (drooping eyelids) or ocular muscle paralysis and diplopia (double vision).
Next, the skeletal muscles controlled by the motor nuclei in the pons and medulla (also known as the bulbopontine nuclei) are affected, including the masticatory muscles, swallowing muscles, and respiratory muscles.
Limb muscles are affected subsequently.
The involved muscles often exhibit lymphocytic inflammatory responses and may even show muscle fiber atrophy.
Prognosis of Myasthenia Gravis: Advances in modern treatment have significantly improved the prognosis for Myasthenia Gravis.
For instance, the mortality rate for this condition was as high as 30-40% from 1900 to 1957, improved to 15% by 1958, and further decreased to 5% between 1970 and 1980.
Nowadays, fatal cases are rare.
Neurologists treat Myasthenia Gravis using acetylcholinesterase inhibitors (such as Mestinon) and corticosteroids (such as prednisone) to suppress the abnormal immune response.
In life-threatening situations or prior to surgery, treatments such as plasmapheresis or intravenous immunoglobulin (IVIG) injections are performed.
Since the abnormal T lymphocytes originate from the thymus, about 85% of patients with this condition will show thymic hyperplasia or thymoma, leading neurologists to recommend early thymectomy.
After thymectomy, approximately one-third of patients will experience complete resolution of symptoms, another one-third will see significant improvement, while the remaining one-third may have no change or continued deterioration.
In terms of natural disease progression, the first 5 to 7 years after onset are critical for prognosis.
Rapidly progressive cases that affect the entire body tend to have a relatively poor prognosis; however, if the condition is limited to the ocular muscles during this period, there is less likelihood of subsequent involvement of other muscles.
Your situation will require further understanding of thymic pathology, serum acetylcholine receptor antibody levels, and medication history to make an assessment.

---

Reply Date: 2005/01/24