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Between 60% and 70% of U.S. residents experience low back pain at least once.¹ The majority of these cases are self-limiting and resolve within about 6 weeks. Although most presentations of lumbar pain have a benign or idiopathic origin, careful attention is needed to identify the few patients who may experience back pan as a result of life-threatening or life-changing pathologies.

The differential diagnoses for low back pain are vast and can include anything from the common lumbar strain to obscure causes such as epidural abscess. Vigilant observation for red flags (Table 1) will help avoid poor outcomes.

History

As with any presenting complaint, a good history of the events leading to low back pain is essential. Specific attention should be paid to the onset of the pain. A history of low back pain after lifting heavy objects or turning in a certain direction is suggestive of lumbar strain that will likely resolve spontaneously with care directed at symptomatic relief.

The presence of sciatica may represent a herniated disk. Sciatica is defined as pain radiating down the back or side of the leg beyond the knee. About 95% of patients with a herniated disk report sciatica, making it a key point in the evaluation of the patient.¹

Bilateral sciatica, along with progressive neurologic symptoms such as bowel or bladder dysfunction, saddle paresthesia or leg weakness, are red flags for cauda equina syndrome and require emergent referral.

A history of back pain with fever and neurologic deficit is the classic red flag finding for an infectious process such as epidural abscess or spondylitis (vertebral osteomyelitis). In one study, only 13% of patients with spinal epidural abscess presented with this triad of complaints.² For this reason, consider risk factors for spinal infection as well as presenting complaints (Table 2). Remember, however, that up to 20% of patients with epidural abscess have none of the listed risk factors, making the diagnosis of this debilitating disease extremely difficult.³

Pain that is more severe at night and does not relent or decrease with rest raises a concern for malignancy. Other red flags for malignancy include back pain with weight loss and pain that has lasted longer than 4 to 6 weeks. A known history of cancer should also be considered.

Physical Examination

Every physical examination of the back should begin with inspection. Have the patient stand erect. While he or she does so, visualize the curvature of the spine. Abnormal curvatures of the spine, such as kyphosis or lordosis, may signal muscle spasm or strain. These curvatures are not likely acute, however, and they may lend little assistance in the determination of pathology for acute back pain.

Next palpate each spinal process and paravertebral muscle. Percuss each spinal process by tapping with one finger and then rapping each side of the spine along the paravertebral muscles using the ulnar aspect of the fist. Muscle spasms can often be detected during this palpation, revealing the etiology of the pain. Tenderness along the spinal process during percussion may indicate infection such as spondylitis.

Ask the patient to bend forward. Note the degree to which he or she is able to perform this function. The expected normal amount of flexion is 75 degrees to 90 degrees. Ask the patient to bend backward. This should demonstrate a hyperextension of about 30 degrees. Lateral movement is considered normal when it is about 35 degrees to each side.⁴ Make note of these angles in the patient's chart during the initial examination. This information is helpful during later exams, to determine the effectiveness of treatment.

When sciatica or herniated disk is a possibility, perform the straight leg raise test. To perform this test, have the patient lie supine on the exam table. Slowly raise each of the patient's legs; the patient should keep each knee locked in the straightened position. Reproduction of the patient's pain between 30 degrees and 70 degrees flexion is considered a positive finding for herniated disk. The straight leg raise test can also be performed while the patient is sitting in the upright position, but the sensitivity of the results are greatly reduced.⁵

Diagnostic Testing

After a thorough history and physical examination, the majority of patients who present with back pain have no specific, identifiable spinal abnormality or disease process. In fact, nearly 85% of patients who present to primary care providers with low back pain have no identifiable abnormality.⁶ With this fact in mind, diagnostic imaging or other studies should be considered when pain continues past 4 to 6 weeks.

Routine imaging is not recommended for patients with low back pain, but NPs should consider computed tomography (CT) or magnetic resonance imaging (MRI) for patients who present with red flags or who experience prolonged pain. Of the two tests, MRI is generally considered the diagnostic study of choice, when available.⁶