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Separating fact from fiction in treating low back pain

From the May 1995 ACP Observer, copyright © 1995 by the American College of Physicians.

By Bob Keaton

How much do you know about treating low back pain? Take this true-or-false quiz:

Bed rest helps.

False. It doesn't, except perhaps in cases of acute sciatica or a disc herniation. In other cases, brief, if any, bed rest is needed.

An MRI will give you the answer.

False. In most cases it won't, and it may even mislead you.

A diagnosis can always be made.

False. It can't. An NIH consensus panel concluded a decade ago that some 85% of all cases of back pain can't be given a precise diagnosis.

Primary care physicians are in an excellent position to help dispel these and other myths and to provide effective therapy for their patients, said Richard A. Deyo, FACP, professor in the departments of medicine and health services at the University of Washington School of Medicine and the School of Public Health in Seattle, during a Meet the Professor session on low back pain.

Studies show that back pain ranks among the top 10 most common diagnoses given by internists. Back pain is also the second most common reason for surgery in this country. It consumes $25 billion of direct medical care costs annually, plus indirect costs such as the cost of work loss, insurance or disability compensation.

Dr. Deyo called for a systematic and rational early approach to treating back pain. In an early diagnostic evaluation, the clinical history and physical examination should go a long way toward answering three key questions:

  • Is there any underlying systemic disease or infection causing the pain? "The good news is that the dreaded diseases we worry about--metastatic cancer, spinal osteomyelitis, epidural abscess--count for only about 1% of the patients with back pain," Dr. Deyo said.

He added that about 80% of patients with an underlying malignancy are over 50 and advised physicians to carefully evaluate any patient with a history of malignancy. "Systemic signs such as unexplained weight loss, lymphadenopathy or hematuria should also prompt further investigation," he said.

The optimal next steps are unclear, but the "lowly sedimentation rate is useful as a screening tool because of its sensitivity, and a plain X-ray can be useful, too." Studies suggest that if the X-ray is normal and the sed rate is normal, the likelihood of underlying cancer is close to zero, he added.

Most spinal infections are blood-borne from another site, he explained. Spine tenderness to percussion is a relatively sensitive finding for bacterial infection and a sed rate can be helpful. Patients with fever should be investigated further.

  • Is there a neurologic deficit that may require surgical evaluation? The most common cause of neurologic impairment in patients with back pain is a herniated disc. Since 95% of disc herniations occur at the lowest two lumbar intervertebral levels, neurologic examinations should emphasize ankle dorsiflexion strength, great toe dorsiflexion strength, ankle reflexes and the sensory examination. Ipsilateral straight leg raising is a moderately sensitive--but non-specific--test for nerve root irritation, Dr. Deyo said. In contrast, a crossed straight leg raising sign (reproduction of leg pain when raising the opposite leg) is a highly specific--but relatively insensitive--sign for nerve root irritation.

The other causes of neurologic impairment to look for include spinal stenosis and cauda equina syndrome. Spinal stenosis typically occurs in older patients, who can experience pain in their legs or neurologic deficits after walking. "Unfortunately, only about 60% of patients who undergo surgery for spinal stenosis have this finding," Dr. Deyo said. Patients with spinal stenosis also experience increased pain when standing, unlike those with herniated discs, who generally find sitting or bending painful.

Cauda equina syndrome is a rare diagnosis, with urinary retention being the most consistent finding (occurring in about 90% of patients). About 75% of patients with this syndrome have "saddle anesthesia," over the buttocks, posterior superior thighs and perineum. In 60% to 80% of the cases, anal sphincter tone is reduced. The cauda equina syndrome is the only indication for emergency surgical referral. Dr. Deyo warned, however, that patients with severe neurologic deficits or those who fail to progress in the face of conservative therapy should also be referred to a surgical specialist.

  • Is there any psychosocial problem that may affect recovery? Depression, substance abuse, obesity, previous back problems or whether the patient is applying for workman's compensation can affect recovery. "Workman's compensation probably tops the list," Dr. Deyo said. "If it's involved there are all kinds of incentives not to get better."

Important tipoffs that psychological factors are at play include patients with numbness in the whole leg, patients whose leg keeps giving way or those who say the pain never changes and that nothing helps. "These are not typical of people with organic causes of pain," Dr. Deyo said.

Plain X-rays, which Dr. Deyo said he believes are overused, can be useful when there is unexplained weight loss, fever or systemic signs. They may also yield useful findings when a patient is not getting better after six weeks of therapy or is over 50 and never had any X-rays. Growing evidence suggests, however, that the traditional five-view X-ray (AP, lateral, two obliques and a coned lateral of the L5-SI junction) is unnecessary for most patients. Limiting the routine lumbar spine X-ray to an AP and lateral eliminates two-thirds of the radiation exposure and costs. At least five studies show that few diagnoses are missed by omitting these views, and those diagnoses in turn rarely affect therapy.

MRI and CT should be reserved as presurgical tests to confirm the diagnosis and help plan for surgery, Dr. Deyo said. Both are expensive and oversensitive, and they often show abnormalities in people who have never had back pain.

Randomized trials show that non-steroidal anti-inflammatory drugs can be effective therapy for low back pain. Muscle relaxants are also effective, but because of the side effects, dosage should be limited to a week or two. Tricyclic antidepressants can be effective in cases where chronic pain and depression coexist, but it is unclear whether they work on chronic back pain without depression.

Clinical trials suggest that exercise helps. Dr. Deyo recommends extension exercise and general fitness exercises for acute situations (after the most severe symptoms subside) and a supervised combined regimen of flexion and extension for chronic situations.

Bob Keaton is an Atlanta-based freelance writer specializing in medical issues.

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