Myasthenia gravis after thymectomy: a case report

Myasthenia gravis (mg) is an acquired autoimmune disease, which occurs at the neuromuscular junction and is mediated by antibodies against acetylcholine receptor and dependent on cellular immunity. Its pathogenesis is related to genetic factors, pathogenic autoantibodies, cytokines, complement participation and thymic muscle cells and other complex factors.

In clinical practice, myasthenia gravis is easy to fatigue after activity, which can be relieved by resting or using cholinesterase inhibitors. It is usually characterized by light in the morning and heavy in the evening with obvious fluctuation. About 2 / 3 cases involved extraocular muscles, often early symptoms, 10% of them were confined to ocular muscles for a long time, while facial muscles, throat muscles, trunk muscles and limb muscles were all involved. The course of the disease is prolonged and can be relieved, relapsed or worsened. Infection, fatigue and so on often aggravate the condition, even appear crisis. In general, the early diagnosis of myasthenia gravis with thymic abnormalities mainly depends on thymic imaging. Although thymic CT can detect lesions early with good histological features, it is difficult to accurately distinguish between thymoma and thymic hyperplasia.

At present, thymectomy is still the basic treatment for myasthenia gravis. It is suitable for patients with systemic myasthenia gravis who have poor drug efficacy or can not tolerate drug treatment, or patients with thymoma. Whether ocular myasthenia gravis should be treated surgically is still controversial. Relevant studies have shown that the earlier the operation is performed after the diagnosis of myasthenia gravis, the greater the benefit of patients. Therefore, it is generally considered that surgical treatment within 3 years after the diagnosis is clear is more appropriate. At present, the surgical approaches of thymectomy for myasthenia gravis include neck incision, partial sternotomy incision and whole sternotomy incision. In recent years, video-assisted thoracoscopic or robot assisted thymectomy has been widely used. Because of the extensive distribution of ectopic thymus tissue in mediastinum, although it is emphasized that thymus and adipose tissue in mediastinum are completely removed during operation, it is difficult to achieve 100% resection. Some literatures have shown that the resection rate of extended thymectomy with cervical incision and sternotomy can reach 85% ~ 95%.

But there are also new cases of myasthenia gravis after thymectomy. We once met a 54 year old female patient who was diagnosed as mediastinal mass with uniform density and intact capsule, with a diameter of about 4 cm × 3 The patients were considered as thymoma without myasthenia and physical activity was the same as that of normal people. The relevant examination should be improved and the operation contraindication should be excluded. Thoracoscopic thymectomy was performed. The postoperative pathology showed thymoma. On the 2nd day, the patient had difficulty in breathing, and had no dyspnea. On the fourth day after the operation, the symptoms were not relieved, and the limbs were weak, accompanied by chest tightness and asthma. Myasthenia gravis was considered, and the neostigmine test was positive, so the diagnosis was confirmed. The patients were given bromopyrimethamine tablets. They could get out of bed on the second day of medication. The symptoms of myasthenia such as choking and weakness of limbs gradually improved. After 5 days, the general symptoms improved and discharged. They continued to take medicine outside the hospital and myasthenia occurred one week after discharge The symptoms disappeared, and bromadine was gradually reduced to discontinuation within 1 month after discharge. No myasthenia recurred during the follow-up.

After operation, the time of ventilator assistance should be prolonged according to the patient’s condition, and the tracheal intubation should be pulled out after the recovery of muscle strength and consciousness. Early postoperative application of anticholinesterase drugs can help patients recover muscle strength, promote active sputum excretion and reduce respiratory tract infection. Tracheotomy should be performed in time if extubation is difficult. 72 hours after operation, the incidence of myasthenia crisis was high. In case of crisis, endotracheal intubation and tracheotomy should be carried out as soon as possible, and the dosage of anticholinesterase drugs and hormones should be adjusted. After the condition is completely stable, the patient will gradually leave the ventilator. After operation, when patients have respiratory fatigue and hypoxemia, whether it is myasthenia crisis or cholinergic crisis, tracheal intubation should be given decisively to improve the ventilation function of patients. At present, most scholars believe that timely use of mechanical ventilation is the main means to reduce the mortality of myasthenia crisis.

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