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Make the Diagnosis: Low Back Pain

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Prior Probability

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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.

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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.

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Population for Whom Herniated Disk With Radiculopathy Should Be Considered

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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).

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Table Graphic Jump Location
Table 7-8Utility of the Clinical Examination for Herniated Disk or Cancer Among Patients With Back Pain
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Population for Whom Cancer Should Be Considered

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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).

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Reference Standard Tests

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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. However, clinicians must ...

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