Arm and leg pain (sciatica) is often due to nerve root irritation caused by disc herniations in the neck or back. Nerve root blocks are both diagnostic and therapeutic. Injection of local anesthetic freezes the pain temporarily which confirms that the nerve is the source of the person’s pain. Cortisone is usually injected at the same time, which reduces the inflammation that is caused by the disc herniation or nerve root compression. Cortisone can relieve pain for weeks or months and sometimes forever.