Why is the levator palpebrae muscle of myasthenia gravis patients most vulnerable?
The first common symptom of myasthenia gravis patients is ptosis, But its mechanism is not clear. Some scholars believe that the levator palpebrae superior muscle is different from other extraocular muscles. For fast shrinkage fibers, It has a high anti-fatigue property and is a muscle fiber that is not innervated by multiple nerves. The levator palpebrae superior muscle has been stimulated by nerve impulses when opening eyes, so its compensation space is small under pathological conditions, and the [reserve] to deal with pathological changes is insufficient, resulting in the safety factor of neuromuscular transmission being easily affected and more easily fatigued than other muscles.
Some studies have also proved that synaptic folds of levator palpebrae superior muscle are less, AChR and Na + channels are less, which is easy to reduce safety factor and aggravate muscle junction transmission disorder under pathological conditions.
In addition, complement is involved in the immunopathological process of myasthenia gravis. The expression of complement regulatory protein in levator palpebrae superior muscle is less than that in other skeletal muscles. Complement regulatory protein can inhibit complement function. If the expression of complement regulatory protein is less, it means that complement activation is not easy to be terminated once activated. Therefore, it can be speculated that levator palpebrae superior muscle is more vulnerable in complement-mediated pathological process.
Follow-up of patients with ocular myasthenia gravis after strabismus correction surgery
Strabismus and blepharoptosis are common clinical manifestations of ocular myasthenia gravis. A recent small sample case study evaluated the long-term prognosis after surgery for ocular myasthenia gravis. The study included 9 patients. Follow-up for at least 6 months after surgery. Evaluation indicators include eyeball position, number of surgeries and sensory state. Among these patients, Horizontal strabismus initially occurred in 2 cases, 3 cases had vertical strabismus, One case had both vertical and torsional strabismus. The average preoperative stabilization time lasted for 2 2.5 years. The mean preoperative horizontal and vertical separation was 40.5 ± 32. 5 PD and 25.6 ± 36. 7 PD (PD=prism diopter) respectively. The mean follow-up time after the first operation was 5.7 ± 4. 2 years. Four patients underwent two operations, The average distance from the first operation was 2.3 years. Six patients showed no strabismus at the last follow-up. Five patients recovered single vision after operation. Conclusion Strabismus surgery can improve the eye position of patients with ocular myasthenia gravis.
In view of the fluctuating condition of myasthenia gravis, strabismus surgery should be carried out at a relatively stable stage, otherwise fluctuation of condition is a contraindication for strabismus surgery!
Treatment Strategy of Adult Simple Ocular Myasthenia Gravis
Ocular myasthenia gravis, Treatment must take into account the patient’s condition and lifestyle, occupation, economic situation, etc. For example, if housewives suffer from ocular myasthenia gravis and are partially effective against pyridostigmine, immunosuppressants are not needed. If it occurs in drivers or doctors, more active treatment is needed due to eyesight and appearance requirements.
Existing experience shows that, Of all immunosuppressive agents, glucocorticoid has the best effect on ocular muscle type. It also works fastest, There is no uniform regimen for hormone treatment of ocular myasthenia gravis. It is generally recommended that 10-20 mg prednisone should be taken daily, and the dose should be increased every few days until the symptoms improve. More than half of the patients will relapse when the hormone is reduced, especially when the hormone is reduced immediately after short-term treatment. Retrospective studies have shown that hormone therapy can reduce the risk of developing systemic type, but prospective studies are needed to confirm it.
Surgical resection is still recommended for patients with simple ocular myasthenia gravis complicated with thymoma. The main purpose of this move is to solve thymoma itself rather than myasthenia gravis. However, surgical treatment is generally not recommended for patients with simple ocular muscle type complicated with thymus hyperplasia. Because the injury to human body caused by the operation itself far exceeds that of ocular muscle myasthenia gravis itself, any medical measure needs to weigh the risk-benefit ratio, which is far greater than the benefit. Therefore, thymectomy is not recommended in patients with simple ocular muscle type, and of course, if it progresses to systemic type, it is another matter!
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