In neurology clinics, muscle weakness is second only to pain, dizziness, numbness and other symptoms, and is very common. The so-called muscle weakness is a subjective sensory symptom, that is, under the action of pathogenic factors resulting in a variety of nerve, muscle and related structural disorders, the appearance of the muscle can not move freely or forceful contraction of the performance. Objectively, muscle weakness can be recognized by comparing the intensity of muscle contraction of the affected limb with that of a normal limb. Once the patient has muscle weakness, if not diagnosed and treated in time, it will have an impact on life and work, and may even leave a permanent disability. Therefore, it is necessary to know some knowledge about muscle weakness accurately and treat muscle weakness actively. Through the knowledge of anatomy and physiology, we know that normal muscle activity and contraction depend on the integrity and joint participation of nerve tissue, muscle joints, and muscle tissue. Any etiology that directly or indirectly causes one or all of the three results in the development of muscle weakness. There are many causes of muscle weakness, which can occur at different ages. Of course, if we understand some of the patterns of its appearance, it may help in proper diagnosis and treatment. Here are some common knowledge about muscle weakness. 1.Myasthenia gravis at different ages: Myasthenia gravis can occur at any age. Myasthenia gravis in infancy and childhood is often related to genetic diseases, mainly neuromuscular or muscular dystrophic disease, which is mainly manifested in infants and young children with weak birth, small cry, little movement, late development, and shorter life expectancy in general. Most of the muscle weakness in adolescence also belongs to neuromuscular or myotonic dystrophy, at this time can often be seen in addition to the weakness of muscle atrophy appears. Myasthenia gravis in middle age and old age can be seen in various types, including vascular, genetic degeneration, metabolic, etc. Therefore, the diagnosis can not be made easily, and it needs to be determined after perfecting various examinations. 2.Myalgia with fluctuating symptoms: it mainly occurs in cerebrovascular disease and neuromuscular junction lesions, such as cerebral blood supply deficiency episodes or periodic paralysis, myasthenia gravis and other diseases, which are characterized by fluctuating symptoms. If treated in time, cerebral blood supply insufficiency and periodic paralysis muscle weakness can be relieved; myasthenia gravis has early light and afternoon heavy changes. 3, accompanied by atrophy of muscle weakness: common in the nerve, muscle itself caused by lesions. Whether it is genetic or various causes of destruction can appear atrophic muscle weakness, such as motor neuron disease, crural compression, myositis, myotonic dystrophy and so on. These abnormalities can be detected by testing muscle enzymes or electromyography, and if it is a compressive lesion, it can also be detected by CT or MRI. 4. Myasthenia gravis with pain: it is common in peripheral neuropathy or inflammatory muscle lesion, and some tumors can cause painful myasthenia gravis when destroying nerves or muscles. 5, muscle weakness with abnormal sensation: in vascular or peripheral neuropathy, it is common to see muscle weakness accompanied by ants, electricity, fire, coldness, tightness, wood and other sensations, such as diabetic peripheral neuropathy, polypoidal peripheral neuropathy and so on. 6, accompanied by muscle tension changes in muscle weakness: the most common disease for the extrapyramidal system of Parkinson’s disease, patients often feel limb “weakness” and slow movement, tremor. In fact, patients do not have muscle strength decline, feel weak because of the muscle tension increases, do the movement is more difficult. 7, accompanied by endocrine abnormalities of muscle weakness: many endocrine and metabolic diseases can be roughly muscle weakness, the most common are hypothyroidism/hyperthyroidism, diabetes and so on. Because these diseases often cause hormone level disorders and immune function abnormalities, so easy to muscle weakness. For the same reason, there are some malignant tumors such as small cell carcinoma of lung also have endocrine function, which can cause muscle weakness and myasthenia gravis, and we call it “paraneoplastic syndrome”. 8.Accompanied with emotional changes of myasthenia gravis: Strictly speaking, myasthenia gravis accompanied with mental and emotional changes can not be called myasthenia gravis, and at most it is called “lack of strength”. This is because this kind of weakness subjectively has the manifestation of weakness, but lacks the objective examination basis of weakness, that is, all kinds of examination is normal. In particular, some patients with vegetative dysfunction and depression, who lack enthusiasm and motivation, are prone to fatigue, which is mistaken for myasthenia gravis. Generally this type of myasthenia gravis is also affected by mood swings and can be identified. For any of the above types of muscle weakness to appear, should be immediately to the hospital for consultation, see a neurologist to clarify the diagnosis. Generally speaking, in addition to the physical examination by the physician, there are also blood enzymology and immunology examination, endocrine examination, tumor examination, etc.; morphology examination often includes CT and MRI; electrophysiology examination has electromyography as an option; nowadays, there are also high-tech examination, such as muscle biopsy and electron microscopy, genetic examination, etc., which provide a guarantee of rapid and accurate diagnosis.