Recently, some authors reported that discogenic low back pain should be regarded as a referred pain in respect of neural pathway. The afferent pathways of discogenic low back pain is transmitted mainly by sympathetic afferent fibres from the sinuvertebral nerves in the second lumbar nerve root. This pain arises from the lumbar intervertebral discs, and it had been transmitted mainly through the sympathetic afferent fibres contained in the second lumbar spinal nerve root. Second lumbar dermatome corresponds to the low back area. We experienced a case of low back pain which could not be controlled by conventional therapy and progressed wax and wane. The CT finding showed bulging disc between $L_4$ and $L_5$ and spinal stenosis in $L_4$ area. And epiduroscopic feature showed severe adhesion in $L_4$, $L_5$ and $S_1$. After we blocked $L_2$ root, pain score decreased 10 to 2. Therefore, the $L_2$ root block may be a useful diagnostic procedure as well as provide therapeutic value.