Motor neuron disease is a disease with increasing incidence and younger age of onset. There is no definitive and effective treatment for this disease. Once detected, it often continues to worsen until death. However, there are many subtypes of this disease. Some subtypes are more critical and progress more rapidly, quickly involving the medulla oblongata and causing respiratory failure and death. In contrast, some subtypes tend to involve only part of the limb in the first few years, progressing more slowly and only worsening or progressing to another part of the limb over many years, with a relatively good prognosis. Then, if these subtypes can be distinguished in a timely manner at an early stage, it will help a lot in the psychological expectation of the patients, at least for some of the slower developing subtypes, so that they do not need to be repeatedly seen, repeatedly examined, and in a state of panic without remission. I often see some patients in the clinic, once they see muscle atrophy, weakness, or even flesh jumping, they will be frightened and seek medical advice everywhere, among them, some are indeed motor neuron disease, but a considerable number of people, not caused by the disease, no need to panic. In terms of muscle atrophy and weakness, any disease that can cause motor nerve damage is possible, and this range is much larger, not necessarily motor neuron disease. In terms of flesh jumping, excessive fatigue, excessive stress, anxiety and depression can all cause flesh jumping, which is not necessarily motor neuron disease. So, what is the difference between motor neuron disease and motor neuron disease? There is only one answer: electromyography plus an accurate neurological examination. The essence of motor neuron disease is unexplained apoptosis of motor neurons or necrosis of their conduction fibers. It is divided into many subtypes depending on the condition. To make an accurate diagnosis, an electromyogram is necessary. So, what will the EMG show? The typical EMG presentation is a large number of spontaneous potentials in the muscles innervated by three or more segments (medulla oblongata, cervical medulla, thoracic medulla, lumbar medulla, etc.), a widening of wave amplitude due to neural compensation, and a vigorous recruitment showing neurogenic damage. Of course, the manifestation varies in severity with the early and late progression of the disease. Early on, damage may be present in only one or two segments, or manifest as only one or two of these three conditions in terms of potentials, but often continues to worsen as time progresses. The most typical feature of motor neuron disease is that there is no plateau, no remission, just continued exacerbation until death. This is also true of the presentation on EMG. Of course this process varies in length with its subtype. One of the subtypes is the brachycephalic type and the brachycephalic leg type, in which muscle atrophy and weakness of both proximal upper limbs and distal lower limbs are found first, without other symptoms. The development of these two types is relatively slow. Only one segmental abnormality is demonstrated on EMG. In contrast, amyotrophic lateral sclerosis tends to progress more rapidly, often involving up to three segments within a few months, and gradually involving the medulla oblongata, manifesting as unfavorable speech, choking on water, and difficulty breathing, with a poorer prognosis. Therefore, at the early stage of detection or suspicion of motor neuron disease, electromyography should be improved as soon as possible to clarify whether it is motor neuron disease? Which segments are involved? What is the possible subtype? What is the prognosis? This is how important the role of EMG is in the diagnosis of motor neuron disease.