118 Korean J Pain Vol. 25, No. 2, 2012 week after the procedure, periods without pain had con- tinued for two to three days and gait abnormality had also disappeared during this period, but at the time of visit, a pain of VAS 5/10 was experienced by the patient. Hence, it was decided that the psoas compartment blockade was effective, so it was performed three times in two week intervals. As a result, the patient has shown improvements in pain of about VAS 3/10, so we are still monitoring his progress. DISCUSSION The psoas muscle is the muscle involved with the curve of the pelvis and spine, which starts at the thoracic verte- brae to connect with the lower vertebral body and trans- verse process. It goes past the pelvis and extends up the lesser trochanter [1]. When standing, it pulls the spine for- ward, while keeping the balance of the body when sitting, so it has an important role during walking motion. There- fore, when the psoas muscle continuously contracts from injury or stress, the vital dynamics of the pelvis, lumbar, and even the cervical vertebrae can be disturbed. This in- congruity can cause pain in the lower back, pelvis, but- tocks, and the femoral region. Also, there could be a transformation in the hip joint curve, and as a result, movement can be limited when using the hip joint. Thus, when there is a problem in the psoas muscle, it can trigger a distinctive psoas gait, where the patient drags their leg while walking as the leg cannot be strongly pushed forward [2]. The differential diagnosis for patients with these symptoms can consider infectious diseases, such as an Fig. 2. Anteroposterior (A) and lateral (B) fluoroscopic images of the psoas com- partment block. abscess in the psoas muscle, hemorrhagic lesions, such as hematoma, and the metastasis of cancer. An abscess in the psoas muscle is not common, but is recently showing an increasing trend. Uncontrollable diabetes can be an im- portant preceding factor [7], and symptoms, such as fever, pain in the side or hip area, and limitation in movement of the hip joints appear. Hemorrhagic lesions, such as hematomas, are known to occur more in patients who are either taking antiplatelet agents or anticoagulant treat- ment, or patients with blood coagulation disorders [8]. It is not common for cancer to spread to the psoas muscle, but for patients with a history of cancer, it must be taken into consideration that the psoas compartment can be a channel for the tumors to directly infiltrate the retro- peritoneal, skeletal muscles, and pelvis [9]. There is also a report that, in a patient with rectal cancer, a biopsy per- formed in suspicion of an abscess in the psoas muscle, re- vealed the metastasis of cancer [10]. Treatment methods can be different for these diseases, such as internal medi- cine and surgery, so an accurate diagnosis is important. After differentiating the suspected diagnosis to a certain degree, through medical history, physical examination, and blood tests, it can be further confirmed through imaging. Our case shows the discovery of the lateral disc her- niation in the MRI. The case of lateral disc herniation is where the disc is herniated to the side of the root foramen, toward the outside of the spinal canal. Lateral disc hernia- tion is a lesion that is easily missed because it is difficult to observe in a MRI image [11]. Even in our case, the re- inforced image of T2 did not show a herniated disc or com- pression of the nerves (Fig. 1C), so if lesions in the psoas www.epain.org