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Correct application of MRI finds causes of low back pain

Correct application of MRI finds causes of low back pain

Low back pain is extremely common in Western society.1 It is second only to upper respiratory illness as a symptom related reason for visits to the doctor.2 Estimates of total costs per capita per year for low back pain in Europe range from €116 to €399.1

It is generally believed that most cases of low back pain are benign and self-limiting. The real challenge for the clinician is to distinguish serious spinal pathology from nonspecic low back pain.3 The patient's history and the clinical, laboratory, and imaging findings may help in differentiating these causes. The history should include an assessment of psychosocial risk factors, which predict risk for chronic disabling back pain.4

The main role of imaging is to rule out serious pathology and/or to detect and localize and target treatable causes. Disc herniations and degenerative disc disease are the most common treatable reasons for low back pain, though only a minority of patients with these conditions will receive appropriately targeted therapy. Other reasons for imaging may include reassuring the patient and/or clinician, monitoring treatment, and following up a known pathology.

ACUTE PAIN

Low back pain is defined as acute during the first six to 12 weeks and chronic thereafter. Imaging is not typically recommended during an initial episode of acute low back pain in the absence of leg pain unless other specific findings are present. These additional “red flag” findings indicate the possibility of a serious underlying condition such as trauma, cauda equina syndrome, progressive neurologic deficit, infection, and/or malignancy.5,6

A detailed discussion of imaging in spinal trauma is beyond the scope of this article. In short, clinical findings and the patient's history are generally used to determine whether imaging is needed, and whether the first-line tool should be plain-film radiography or CT. Minor trauma may cause compression fractures in patients who are elderly, have a history of osteoporosis, and/or take steroids.

Cauda equina syndrome is typically characterized by low back pain, sciatica, lower extremity sensorimotor loss, and bowel and/or bladder dysfunction. Full-blown cauda equina syndrome includes urinary retention, saddle paresthesia of the perineum, bilateral lower extremity pain, numbness, and weakness. 7 The pathophysiology remains unclear, though damage to the nerve roots composing the cauda equina, from either direct mechanical compression or venous congestion and/or ischemia, may be a contributory cause.

Early diagnosis is often challenging because the initial signs and symptoms are frequently subtle.7 Given that the preferred treatment strategy is urgent surgical decompression of the spinal canal, imaging is a cornerstone in the workup of these patients. Frequent causes of cauda equina syndrome include disc herniation, trauma, and/ or vertebral metastasis with secondary spinal stenosis and compression of the cauda equina. MRI is regarded as the modality of choice owing to the diversity of potential causes of compression, and difficulty ascertaining the thoracolumbar level of compression.

Spinal infections can occur in the bone of the vertebral column, the intervertebral disc space, the spinal canal, or any combination of these locations. Only 0.01% of patients presenting with low back pain will have a spinal infection. These infections are most commonly caused by bacteria and can cause significant levels of pain.

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