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Make the Diagnosis: Low Back Pain

Prior Probability

Because of the weak associations among symptoms, physical findings, imaging results, and electromyograms, a majority of patients with low back pain (≍ 85%) cannot be given a definitive diagnosis. Among asymptomatic individuals, 20% to 30% have evidence of a herniated disk on computed tomography (CT) or MRI. However, only small portions (2%) of individuals with low back pain eventually undergo surgery for disk herniation. Thus, the prevalence of clinically important disk herniations is low.

In the primary care setting, the prevalence of compression fracture and spondylolisthesis is small, at 4% and 3%, respectively, in patients with low back pain. Fortunately, low back pain as a result of spinal malignancy, ankylosing spondylitis, or spinal infection is rare. The prevalence of these conditions among patients with back pain is approximately 0.7%, 0.3%, and 0.01%, respectively.

Population for Whom Herniated Disk With Radiculopathy Should Be Considered

Although it accounts for less than 1% of patients with back pain, cancer is the most common of systemic causes. Cancer should be considered as a possible cause of low back pain in patients older than 50 years with low back pain and in patients with a history of cancer (especially prostate, lung, or breast carcinoma). In addition, patients who fail to improve after 4 to 6 weeks of conservative therapy should be evaluated for underlying systemic diseases such as cancer (Table 7-8).

Table 7-8Utility of the Clinical Examination for Herniated Disk or Cancer Among Patients With Back Pain

Population for Whom Cancer Should Be Considered

A herniated disk with radiculopathy should be considered in any adult with back and leg pain. Herniated disks causing sciatica are most common in middle-aged adults (30-55 years) and are somewhat less common in older adults (Table 7-8).

Reference Standard Tests

For herniated disks, surgical findings may be a gold standard for diagnosis, but back surgery should never be considered just to confirm the absence of a disk hernia among patients with a negative clinical and imaging examination result. For patients who do not undergo surgery, CT or MRI demonstrating a disk herniation with nerve root impingement might be considered a gold standard. In addition, electromyography may confirm nerve root involvement. ...

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