It is an autoimmune disorder characterized by impaired transmission at the neuromuscular junction of striated muscles, featuring muscle fatigue that worsens as the day progresses and improves with rest. It commonly affects the extraocular muscles, masticatory muscles, swallowing muscles, and respiratory muscles. In severe cases, it can lead to bulbar palsy.

bubble_chart Diagnosis

1. Medical history and symptoms:

Common in adolescents and children, often presenting with ptosis, diplopia, difficulty chewing or swallowing, or limb weakness that worsens after activity, leading to medical consultation.

2. Physical examination findings:

Ocular muscle paralysis, weakened limb muscle endurance, positive fatigue test. Repeated performance of the same action or continuous tapping of a reflex in the affected muscles may show a gradual weakening or loss of response.

3. Auxiliary examinations:

1. Neostigmine test: Intramuscular injection of 0.5–1 mg of neostigmine methylsulfate. If muscle strength significantly improves within 0.5–1 hour, the test is positive and confirms the diagnosis. To prevent muscarinic side effects of neostigmine, 0.5–1 mg of atropine should be administered intramuscularly simultaneously.

2. Immunological tests may show abnormalities.

3. Elevated levels of serum cholinesterase, immunoglobulins, and acetylcholine receptor antibody titers.

4. Chest X-ray or CT may reveal thymic enlargement or tumors.

5. ECG may show abnormalities.

6. Electrophysiological examination: Rapid disappearance of response to sustained faradic stimulation of affected muscles. EMG: Repetitive frequency stimulation shows amplitude decrement with low-frequency stimulation and amplitude increment with high-frequency stimulation. A decrement exceeding 10% of the initial amplitude or an increment exceeding 50% is considered positive.

Conditions to exclude include thyrotoxic myopathy, polymyositis, Guillain-Barré syndrome, periodic paralysis, and paraneoplastic myasthenic syndrome.

bubble_chart Treatment Measures

1. Anticholinesterase drugs: Pyridostigmine 60-240mg/dose, taken orally 3-5 times a day.

2. Immunosuppressants:

For patients unresponsive to cholinesterase inhibitors, select based on immune function. Take prednisone 30-60mg/dose daily for 3-5 months, or administer cyclophosphamide 200mg mixed with 25% glucose 20ml and vitamin B6 100-200mg intravenously every other day for a total of 20 doses as one course.

3. High-dose intravenous immunoglobulin:

100-200mg/kg, diluted in 500ml of normal saline and administered intravenously once or twice a week.

4. Plasma exchange therapy:

Available in qualified hospitals, exchange 1000-1500ml per session, twice a week.

5. For patients unresponsive to medical treatment and with thymoma:

Radiotherapy or tumor resection may be performed.