Neurogenic pain in the low back region can be associated with herpes zoster as manifest in shingles or in femoral nerve mononeuropathy that is often associated with diabetes. Pain is due to loss of the pain inhibitory system in the central or peripheral nervous system. It is described as burning, tingling, or skin crawling. It is intensified by what would otherwise be nonpainful sensory stimulation, such as light touch (allodynia). It may persist after cessation of the provoking stimulus (hyperpathia).
Additionally, pain of remote origin, even outside the spine itself, can present as lumbar pain. Lesions within the central nervous system, and in the spinal cord at or above the lumbar area, can also produce both low back pain and radicular leg discomfort. Parasagittal brain tumors and thoracic root lesions, including neurofibromata, can simulate lumbar root syndromes.
Distal nerve entrapment syndromes also can present with primary complaints of lumbosacral pain. The most notable example of this situation is tibial nerve entrapment (S1) in the tarsal tunnel behind the medial ankle malleolus.
Pain to direct palpation over the ischial tuberosities, greater trochanters, or sciatic notches may suggest localized abnormality, including a bursitis at the tuberosity or trochanter or an enthesitis; that is, inflammation at the tendinous attachment of muscle to bone, at the insertion of the hip abductor and extensor muscle groups. Trochanteric bursitis itself can mimic lumbar radiculopathy with distal pain referral along the iliotibial band to the lateral knee. Excessive lateral trunk sway to the stance leg during ambulation, a compensated Trendelenburg gait, suggests primary intraarticular hip abnormality. On examination, corroborative evidence of an initial loss of hip internal rotation may be associated with medial groin pain and a positive Patrick sign, which may radiate to the knee. Attempting to "walk around," primary hip disease produces excessive stress at both the ipsilateral sacroiliac joint and the greater trochanter. Each, singly or together, may initially appear to be the salient problem until the loss of hip mobility is identified as the progenitor of the other complaints.
Based on their shared segmental innervation, pain from visceral disorders, including those of kidney, pancreas, and gallbladder; duodenal ulcers; colonic diverticulitis; expanding abdominal aortic aneurysm; epidural hematoma or abscess; and endometriosis, can all mimic primary low back disorders. Pain from a leaking abdominal aortic aneurysm is constant and aching and may be referred to the lower abdomen and inguinal areas as well as the low back. In the evaluation of low back pain in the elderly, an abdominal aortic aneurysm must always be considered in the differential diagnosis. Costovertebral angle percussion pain is invariably associated with retroperitoneal pathology, most often kidney. Spinal cord compression can develop as a first sign of malignancy or as a complication. It is usually associated with back pain and should always be suspected if there are any neurologic signs or sphincter dysfunction. A history of associated systemic symptoms and a lack of therapeutic response to a trial of initial bedrest, combined with an abnormal abdominal, pelvic, neurologic, or rectal examination, are usually sufficient to redirect the examination to the appropriate extraspinal problem.12
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