Masticatory muscle weakness is mostly seen in the following three conditions: 1. myasthenia gravis, when myasthenia gravis involves the masticatory muscles, pathological easy fatigue can occur, as shown by the patient’s symptoms are not obvious at the beginning of feeding, with the prolongation of feeding time, the symptoms will gradually worsen after the masticatory muscle activity. This disease has a positive neostigmine test and is often associated with thymoma or other autoimmune diseases. 2. polymyositis, in which the skeletal muscles of the patient’s entire body can be involved, with markedly elevated blood muscle enzymes, elevated inflammatory indicators, and localized muscle pain. 3. progressive myotonic dystrophy, a chronic genetic disease, in which the patient’s symptoms appear insidiously and worsen progressively, and in which the weakness of the masticatory muscles is accompanied by other parts of the body. The patient’s symptoms are insidious, progressive, and accompanied by weakness in the masticatory muscles and weakness in other muscles, and the serum muscle enzyme profile is significantly elevated.