As mentioned at different points in this chapter, there is a high rate of inconsequential lumbar spine abnormalities in the general population who have no back or radicular symptoms but it is interesting that disc herniation is found on MRI in under 1 percent (Jensen and colleagues). Administration of gadolinium at the time of MRI enhances regions of inflammation and tumor but is not particularly helpful in cases of degenerative and disc disease of the spine. The decision to administer an intravenous contrast agent depends on the degree of suspicion of infiltration of the bones or spinal canal by cancer or the need to detect spinal nerve root tumors. MRI has replaced conventional myelography for the examination of spinal disease but the latter examination, when combined with CT, provides detailed information about the dural sleeves that surround the spinal roots, disclosing subtle truncations caused by laterally situated disc herniations and at times revealing surface abnormalities of the spinal cord, such as arteriovenous malformations. When metallic devices, such as a pacemaker, preclude the performance of MRI, CT, with or without myelography, remains very useful for diagnosis.
Nerve conduction studies and electromyography (EMG) are also helpful in suspected root and nerve diseases as indicated further on in the discussion of lumbar disc disease. However, all the aforementioned tests must be interpreted in the context of the history and clinical examination; otherwise they are subject to overuse and overinterpretation.
Conditions Giving Rise to Pain in the Lower Back
Peptic ulcer disease and carcinoma of the stomach and pancreas most typically induce pain in the epigastric region. However, if the posterior stomach wall is involved, particularly if there is retroperitoneal extension, the pain may be felt in the thoracic spine, centrally or to one or both sides. If intense, it may seem to encircle the body. The back pain tends to reflect the temporal characteristics of the pain from the affected organ; for example, if caused by peptic ulceration, it appears about 2 h after a meal and is relieved by food and antacids. Diseases of the pancreas are apt to cause pain in the back, being more to the right of the spine if the head of the pancreas is involved and to the left if the body and tail are implicated. Retroperitoneal neoplasms—for example, lymphomas, renal cell tumors, sarcomas, and other malignancies—may evoke pain in the lower thoracic or lumbar spine with a tendency to radiate to the lower part of the abdomen, groins, anterior thighs, or flank. A tumor in the iliopsoas region often produces a unilateral lumbar ache with radiation toward the groin and labia or testicle; there may also be signs of involvement of the upper lumbar spinal roots. An aneurysm of the abdominal aorta may induce pain localized to an analogous region of the spine. The sudden appearance of lumbar pain in a patient receiving anticoagulants should arouse suspicion of retroperitoneal bleeding; this pain may also be referred to the groin. Retroperitoneal appendicitis may have an odd referral of pain to the low flank and back.