There are several possible causes of the fourth finger of the left hand: first, neuritis and neuroma of the finger, which can lead to symptoms of finger woodiness and should be diagnosed by physical examination. Second, nerve entrapment, if the ulnar nerve sulcus of the elbow joint is entrapped, the symptoms of the fourth finger of the left hand can occur, and the diagnosis should be made by physical examination and electromyography. Third, cervical spondylosis, when the cervical spondylosis compresses the nerve root, the symptoms of the fourth finger of the left hand can also appear, then the diagnosis and treatment should be carried out by cervical spine X-ray, CT, nuclear magnetic examination. Fourth, head disease, if there is a tumor in the head, compression of the nerve, can also appear the symptoms of the fourth finger of the left hand wood, then the diagnosis and treatment should be carried out for the head of the nuclear magnetic examination.