The day before yesterday, I saw a 70-year-old woman, supporting her child, come in. She complained of pain in the lateral left calf for 2 weeks. Present medical history: 2 weeks ago, she suddenly had pain in the lateral left calf, accompanied by pain in the posterior side of the lateral left thigh. He visited a nearby Chinese medicine hospital and checked the CT of lumbar spine, which showed that the lumbar spine with multiple discs was herniated and treated with small acupuncture and nerve root closure. However, the pain recurred quickly on both occasions. The orthopaedic surgeon suggested to open the surgery and play the nail. The patient was indecisive and came to my clinic. Physical examination: left straight leg raise test, significant pressure pain in the lateral calf, no obvious skin changes. Preliminary diagnosis: sciatica, suspected to be caused by lumbar disc herniation, but the straight leg raising test was not consistent. Treatment: Since he had just undergone nerve root treatment at an outside hospital, a sciatic nerve block was decided, and the family agreed. Procedure: First, ultrasound observation revealed mild inflammation of the left lateral calf muscle, but it was not obvious. He saw signs of plaster behind the knee (above the N fossa) and asked the patient, complaining that the N fossa was also painful, but the calf was more painful. Ultrasound observation of the sciatic nerve revealed significant inflammatory adhesions of the sciatic nerve to the surrounding muscle tissue 10 cm above the N fossa, and the intact sciatic nerve was visible further up. Therefore, sciatic neuritis was judged. Under ultrasound guidance from the posterior aspect of the thigh, the needle was advanced to the inflamed common peroneal nerve, and the patient clearly felt an overdrive-like tingling to the lateral calf, injected medication into the peroneal nerve of the sciatic nerve, and injected a small amount of medication into the surrounding muscles with inflammation. There was no injection into the patient’s painful calf. 1 minute later the patient’s calf pain was completely relieved. Tracing the medical history, the weather was suddenly cold some time ago, and it is possible that the back side of the thigh got cold at night, and the inflammation stimulated the sciatic nerve after getting cold, which led to the pain in the calf. The patient’s history was traced back to the previous period of time when the weather was suddenly cold at night on the back side of the thigh.