After physical neurological examinations, pain questionnaire will be applied for initial pain evaluation which includes pain intensity and character and physical activity and emotion influence form their pain. Patients then will be performed the first MRI/fMRI study (with the MRI informed consent, appendix B) for their lumbar spine and brain condition. Anyone who don't have shown spine problem will be excluded for epidural steroid injection. After patients' MRI/fMRI evaluation, caudal epidural steroid injection (Regiment: 0.2% lidocaine plus kenacort 40 mg for 20 ml,) will then be performed in pain therapy room ( with the Epidural informed consent, appendix C). Caudal epidural block will be performed 2-3 times with 2 week interval to reach optimal analgesia. The pain condition will be followed every month with pain questionnaire for up 3 month. The secondary MRI/fMRI will then be performed 3 months later after the first caudal epidural steroid injection.