Numbness and pain in the left leg: 1. If it is sudden, it is considered to be caused by cerebrovascular disease, which can be seen in the thalamus lesion, and can be caused by thalamic infarction, occupancy or microhemorrhage, and can be diagnosed by head CT or MRI. 2. Clinically, it can be seen in the lumbar intervertebral disc herniation, as the herniated lumbar intervertebral disc presses on the dural sac, and stimulates the nerve root, which can lead to the left leg numbness and pain, and can lead to radiating pain when it is serious. 3. Clinically, it can also be seen in the spinal cord occupation, there can be sensory abnormalities, nuclear magnetic examination can be found in the spinal cord occupation. 4, clinically, it can also be seen in the peripheral nerve injury of the left leg, it can be traumatic injury, it can be caused by exposure to toxic chemicals, you can check the electromyography to confirm the diagnosis. 5, clinically, it can also be seen in the lower limb arteriosclerosis occlusive disease, there can be weakness, pain, numbness and pain in the left leg, it can be seen in the left leg, it can be seen in the lower limb arteriosclerosis occlusive disease. Left leg weakness, pain, numbness symptoms are relatively light, while lower extremity venous thrombosis can also appear in the left leg pain, swelling, numbness symptoms are not heavy, if necessary, you can check the left side of the lower extremity arterial ultrasound.