Sudden hand weakness can be seen in cervical spondylosis, cerebrovascular disease and epilepsy. 1. When patients have cervical spondylosis, and after prolonged work, the herniated intervertebral disc affects the dural sac and nerve root, thus causing muscle atrophy of the upper limbs, accompanied by numbness of the hands and so on. 2. If the patient has risk factors of cerebral arteriosclerosis such as hypertension and diabetes mellitus, acute cerebral infarction and cerebral hemorrhage may easily occur, resulting in sudden weakness when writing, which may be accompanied by dizziness, headache and unstable blood pressure. 3. Considering the existence of epilepsy, atonic seizures of the upper limbs are prone to sudden weakness when writing, and the seizure time is short, if this phenomenon occurs more, it is necessary to consult a doctor in time for a clear diagnosis and timely treatment. In conclusion, the cause of sudden weakness in writing is complicated, and the patient should seek medical treatment through CT, MRI, electromyography and other clinical tests in order to make a clear diagnosis.