rotation (FAIR) test, revealed no specific findings except tenderness at the right piriformis muscle and greater sci- atic notch. The patient had previously had a total hyster- ectomy, due to cervical intraepithelial carcinoma 18 years before, as well as a few treatments of radiotherapy and chemotherapy for local recurrence and metastasis. Magnetic resonance imaging (MRI), performed at the time of the visit, showed no specific findings except a minimal diffuse bulging disc at the L3-4 and L4-5. There was no specific finding from the electromyography. There were no findings either by the pelvis MRI or the PET-CT, which may cause lumbosacral plexopathy or sciatic neuropathy by local recurrence and metastatic lesion. No inflammatory finding was revealed in the blood test. Although trigger point injection, epidural steroid injection, lumbar sym- pathetic ganglion blockade, and sacroiliac joint injection were performed to treat the pain, they only resulted in temporary pain relief with no continued improvement. In spite of oral administration of narcotic analgesics, the pain became even more severe. Seven to eight months later, the patient reported decreased leg strength and severe (VAS 7-8/10 score) pain at the buttock and thigh. The decrease in leg strength was limited to under the knee, and the dor- siflexion of the ankle and the plantar flexion was lowered to 3/5 grade, but no muscular atrophy was observed. Though the lumbar spine MRI at that time showed no sig- nificant change in spinal lesion, fatty atrophy was found Fig. 1. Fluoroscopic anteroposterior myogram of the piri- formis. Note contrast flow along the distribution of the piriformis muscle. SY Jeon, et al / Post-radiation Piriformis Syndrome 89 at the right piriformis muscle. In addition, the electro- myography showed right sciatic neuropathy. Suspecting the nerve entrapment syndrome by fatty muscle atrophy, local anesthetic and steroid were injected to the piriformis muscle under the fluoroscopic guide (Fig. 1). After the in- jection, the pain was maintained at the level of VAS 1-2/10 for a few months, but the reduced leg muscle strength was not recovered. After that, no additional treatment was performed because the patient rejected further treatment. DISCUSSION 　　Piriformis syndrome is the uncertain disease entity that pathologic conditions of the piriformis muscle cause pain at the buttocks and legs. The major symptom is pain in the buttock while in the sitting position or pain that is worsened by movement of the legs, sometimes accom- panying pain in the legs. The typical findings include ten- derness on the buttocks from the sacrum to greater tro- chanter without the symptoms at the lower back or hip joint, piriformis muscle tenderness according to pelvic or rectal examination, or pain which is aggravated by FAIR positions. Discrepancy in leg length, weakened pelvis ab- ductor muscles, and pain due to pelvis muscles abduction against resistance in the sitting position can be the find- ings as well [1]. It has been known that pressure on the sciatic nerve by piriformis muscles causes such symptoms. Usually, piriformis syndrome is clinically diagnosed by the symptoms and physical examination, and a definite re- search result has not been reported yet. Recently, it has been possible to evaluate anatomical variation in the sci- atic nerve and piriformis muscles and the sciatic nerve en- trapment of piriformis and adjacent tissue by means of magnetic resonance neurography and an interventional MRI so that a more precise diagnosis and treatment can be possible [4,5]. Through electromyography, normal find- ings are usually shown at the initial stage, but abnormal spontaneous activity can be observed as the pressure on the sciatic nerve continues. On the other hand, it has been known that normal findings in the paraspinal muscles of the lumbosacral spine can be helpful for differentiating radiculoparhy, and peroneal division of sciatic nerve is more susceptible to compression or entrapment [6]. In this case study, the electromyographic findings of paraspinal muscles were normal, which fit with the diagnosis of pir- iformis syndrome, but the neuropathic finding in the tibial