Imaging studies for acute low back pain

Postgraduate Medicine ISSN: 0032-5481 (Print) 1941-9260 (Online) Journal homepage: http://www.tandfonline.com/loi/ipgm20 Imaging studies for acute low back pain Thomas O. Staiger MD, Douglas S. Paauw MD, Richard A. Deyo MD & Jeffrey G. Jarvik MD To cite this article: Thomas O. Staiger MD, Douglas S. Paauw MD, Richard A. Deyo MD & Jeffrey G. Jarvik MD (1999) Imaging studies for acute low back pain, Postgraduate Medicine, 105:4, 161-172, DOI: 10.3810/pgm.1999.04.682 To link to this article: http://dx.doi.org/10.3810/pgm.1999.04.682 Published online: 30 Jun 2015. Submit your article to this journal Article views: 7 View related articles Citing articles: 3 View citing articles Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ipgm20 Download by: [The UC San Diego Library] Date: 04 May 2017, At: 15:17 Imaging studies for acute low back pain When and when not to order them Thomas 0. Staiger, MD DouglasS. Paauw, MD Richard A. Deyo, MD PREVIEW Acute low back pain is generally a self-limited condition, and most patients recover within a few weeks without the need for imaging studies. However, physicians need to be on the lookout for red flags that point to more serious conditions, such as infection or malignancy, which require imaging. In this article, the authors identify these warning signs and discuss the appropriate use of imaging studies for a variety of symptoms and conditions. E very year, roughly 50% of working adults experience low back pain. Of these, about 90% recover to tolerance of activities within 1 month and about 2% have symptoms of sciatica (radicular pain radiating down the posterior or lateral leg, usually to the foot or ankle). More than half of patients with sciaticaimprove substantially within 6 weeks, and only 5% to 10% eventually require surgery. 1 The approach to evaluation of low back pain varies considerably among physicians, and current evidence suggests that many of the tests performed are unnecessary. To evaluate the approach taken in 183 patients, Schroth and associates 2 used recommendations for management of low back pain similar to the 1994 guidelines of the Agency for Health Care Policy and Research (AHCPR). 3 The investigators concluded that 10 (26%) of 38lumbar spine films and 12 (66%) of 18 computed tomography (CT) and magnetic resonance imaging ( MRI) scans were inappropriate. Carey and Garretr4 found that overuse of imaging studies ranged from 20% among primary care physicians to 70% among orthopedists. Disadvantages of overuse include gonadal radiation exposures, increased costs, and irrelevant findings that can lead to inappropriate diagnoses and treatment. Up to 25% of asymptomatic adults show degenerative changes on plain films of the lumbar spine. Jensen and associates5 found that 52% of adults without back pain had bulging disks and 28% had disk herniations (figure 1). Of the latter, 27% had disk protrusions and 1% had disk extrusions (distinct and VOL 105/ NO 4/ APRIL 1999/ POSTGRADUATE MEDICINE /IMAGING Jeffrey G. Jarvik, MD potentially more clinically important extensions of the disk beyond the interspaces). Warning signs of serious conditions In most cases of back pain of less than 4 weeks' duration, history taking and physical examination are sufficient for evaluation. 3 The history may reveal red flags that suggest an increased risk of neoplasm or infection. Such warning signs include history of cancer, constitutional symptoms (eg, fever, weight loss), risk factors for infection ( eg, recent bacterial infection, intravenous drug use, immunocompromised state), pain that is not diminished by rest, and age over 50. Warning signs of possible spinal fracture are major trauma ( eg, motor vehicle accident, blunt trauma, fall from a height), minor trauma in a patient over 50, prolonged corticosteroid use, osteoporosis, and age over 70. Symptoms suggestive of cauda equina syndrome, which requires urgent surgical consultation, include saddle anesthesia (found in 75% of patients), recent onset of bladder or bowel dysfunction (with urinary retencontinued 161 Imaging, continued Figure 1. Magnetic resonance Imaging scan of asymptomatic patient with disk herniations at L4·5 (long arrow) and L5·S1 (arrowhead) and a bulging disk at L3·4 (short arrow). tion the most common symptom), and severe or progressive lower extremity weakness. Symptoms and signs that suggest back pain from nonspinous causes, such as subclinical pyelonephritis, kidney stones, or dissecting aneurysm, should also be considered. The AHCPR guidelines for evaluation and treatment of low back pain, 3 which were based on a review of over 10,000 studies, suggest that back pain of less than 3 months' duration can be categorized according to findings of a focused patient history and physical examination. The categories are ( 1) potentially serious underlying conditions, such as neoplasm, infection, fracture, or major neurologic compromise, ( 2) sciatica symptoms, which suggest lumbosacral nerve root impingement, or (3) nonspecific symptoms, often caused by musculoligamentous or degenerative changes, which suggest neither a potentially serious underlying condition nor a nerve root impingement. Most patients with acute or recurrent low back pain fall into the third category; they recover spontaneously or improve significantly within 4 weeks and require no diagnostic studies. Nonradicular back pain If patients have no history of trauma and no warning signs of Thomas 0. Staiger, MD, DouglasS. Paauw, MD, Richard A. Deyo, MD, and JeHrey G. Jarvlk, MD Dr Staiger is assistant professor, Dr Paauw is associate professor, and Dr Deyo is professor, depart· ment of medicine; and Dr Jarvik is assistant professor, department of radiology; University of Washington School of Medicine, Seattle. Correspondence: Thomas 0. Staiger, MD, Department of Medicine, Box 354760, University of Washington School of Medicine, Seattle, WA 98195. E-mail: [email protected]. a potentially serious underlying condition, it is reasonable to wait 4 weeks before ordering lumbar spine films (table 1); 90% of such patients experience significant improvement over this time. Findings on plain films correlate poorly with low back symptoms. Many patients who show degenerative changes on plain films have no low back symptoms, and many patients with back pain do not have any degenerative changes. Generally, when plain films are ordered, they should be limited to anteroposterior and lateral views. Oblique and coned lateral views significantly increase radiation exposure in patients, particularly women, and have been shown to add little new diagnostic information. If symptoms do not improve within 4 weeks, a complete blood cell (CBC) count and an erythrocyte sedimentation rate (ESR) can be helpful in identifying those patients at risk for occult neoplasms or osteomyelitis. In 1988, Deyo and Diehl6 studied 1,975 walk-in patients with back pain and found occult neoplasms in 13 (0.66%). An ESR greater than 20 mm/hr was 78% sensitive and 33% specific in detecting malignancy, while anemia was 54% sensitive and 14% specific. Every patient with cancer had either an abnormal film, an elevated ESR, or both. An elevated ESR is generally believed to be continued 162 IMAGING I VOL 105/ NO 4/ APRIL 1999/ POSTGRADUATE MEDICINE Imaging, continued quite sensitive in detecting osteomyelitis, but the level of sensitivity has not been well established. If, on the basis of red flags or laboratory findings, an occult infection or neoplasm is suspected, bone scan can be moderately sensitive in detecting these conditions.3 An alternative test is MRI; it provides greater sensitivity, specificity, and anatomic definition at a cost roughly twice that of bone scan. 7 Plain films of patients with persistent back pain sometimes indicate spondylolisthesis, a forward slippage of a vertebra over the vertebra below, most common at the L5-Sl joint. Mild spondylolisthesis may be asymptomatic, but about 15% of patients have radicular symptoms. Conservative treatment is indicated initially for patients who do not have neurologic symptoms. Patients with intractable pain that does not respond to conservative treatment or those who have neurologic symptoms may benefit from surgical consultation to determine whether CT, MRI, bone scan, or flexionextension films are warranted. 8 Radicular back pain About 95% of clinically important disk herniations occur at the L4-5 or the L5-Sl disk level. Herniations of these disks, along with root compression, can cause Table 1. Appropriate imaging studies in patients with low back pain Findings Nonradicular pain No history of trauma or red flags Study Wait 4 weeks for back films (limit to anteroposterior and lateral views) Occult infection or neoplasm suspected Bone scan or MRI Spondylolisthesis that does not respond to conservative treatment or accompanied by neurologic symptoms Consider surgical consultation regarding selection of flexionextension films, CT, MRI, or bone scan Radicular pain Persistent sciatic symptoms with obvious level of nerve root impingement MRI or referral to surgeon Sciatic symptoms but nerve root dysfunction ambiguous EMG, CT, MRI, or surgical consultation Trauma Motor vehicle accident or minor trauma in patients at risk for osteoporosis Suspected osteomyelitis Point tenderness over vertebrae and fever History of malignancy Abnormalities consistent with metastatic disease Lumbar spine film after careful assessment of mechanism of injury and identification of other red flags (eg, age, pain not relieved by rest) Plain film initially; MRI if there is a high index of suspicion after initial workup Plain film, bone scan, or MRI CT, computed tomography; EMG, electromyography; MRI, magnetic resonance imaging. continued VOL 105/ NO 4 I APRIL 1999/ POSTGRADUATE MEDICINE /IMAGING 165 Imaging, continued Surgery should be avoided for the first 3 months after onset of symptoms in patients with spinal stenosis, because some patients spontaneously improve. pain or numbness that radiates from the posterior thigh down into the foot. Sciatic symptoms are so sensitive (95%) in detecting disk herniation that a clinically meaningful disk herniation is very unlikely in their absence. 9 Impingement at the L2-3 or L3-4 disk level is seen in 2% to 5% of disk herniations. Patients with this condition present with pain or numbness in the posterolateral or anterior thigh that radiates to the anteromedial knee. Sciatic pain that occurs with straight-leg raising of less than 60° is 80% sensitive in detecting disk herniation but is a nonspecific finding, because limitation caused by pain is commonly seen in the absence of disk herniation as well. The most common neurologic findings in patients with low back pain and leg symptoms are weakness of ankle and great toe dorsiflexion (L-5), decreased ankle reflexes or plantar flexion strength (S-1), and decreased foot sensation (L-4, L-5, and S-1). Except for the small number of patients with cauda equina symptoms or those with rapidly progressing neurologic compromise, who require immediate sur- gical consultation, patients with low back pain and sciatic symptoms should receive conservative treatment during the first 4 weeks. If a patient who is a surgical candidate has not improved after 4 to 6 weeks and has an obvious level of nerve root impingement on examination, MRI or referral to a surgeon is warranted. If a potential surgical candidate has sciatic symptoms, but nerve root dysfunction is ambiguous on examination, electromyography (EMG) may be warranted to determine whether nerve root impingement is present. Other approaches could include CT or MRI scans or consultation with a surgeon to determine further workup. Many patients with spinal stenosis experience neurogenic claudication, which causes back and leg pain, sometimes accompanied by numbness and weakness, that is exacerbated by walking and relieved by spine flexion. Other patients experience positional radiculopathy manifested by radiating leg pain or paresthesia when standing erect or bending backward. 10 Few studies have compared surgical with nonsurgi- cal outcomes in patients with spinal stenosis. Surgery should generally be avoided for the first 3 months after onset of symptoms, because some patients spontaneously improve. Patients with severe or persistent pain often experience decreased pain and improved walking after surgery, although these improvements may deteriorate with time. Further evaluation in surgical candidates with intractable or progressive symptoms can include MRI, CT, or EMG with sensory evoked potentials. Consultation with a surgeon may be useful before selecting a diagnostic test. Patients with history of trauma Risk factors for fractures include a history of major trauma ( eg, motor vehicle accident) or of minor trauma in patients at risk for osteoporosis. 3 Little published evidence exists to assist physicians in selecting which patients with history of trauma are at the highest risk for fractures. Many patients who have been in a lowspeed motor vehicle accident subsequently experience musculoligamentous low back pain; few have pain due to fracture. In the absence of tested guidelines, such as those published for ankle and cervical spine injuries, physicians evaluating the need for lumbar spine films in ambulatory patients with a history of trauma should continued on page 171 166 IMAGING I VOL 105 I NO 4 I APRIL 1999 I POSTGRADUATE MEDICINE Imaging, continued carefully assess the mechanism of injury experienced by each patient. In addition, physicians should look for other red flags, such as advanced age or pain that is not relieved by rest, which would make fracture more likely. Patients with suspected osteomyelitis Risk factors for the development of pyogenic vertebral osteomyelitis include a history of intravenous drug use or recent skin infection, urinary tract infection, instrumentation, or surgery. Physical examination findings that suggest further workup for vertebral infections include point tenderness over the vertebrae and fever. Initial workup should include CBC count, ESR, and urinalysis. If a high index of suspicion still remains after completion of these tests, spinal imaging is warranted. According to the AHCPR guidelines/ a plain film should be considered as the initial imaging study, supplemented by other studies if findings are normal. The sensitivity of plain films is poor because radiographic abnormalities show up late (2 to 8 weeks after symptoms begin)Y MRI provides a high sensitivity (96%) and specificity (92%) in diagnosis of spinal infection. 12 Involvement of the vertebral bodies, disks, and paravertebral region can be seen better with MRI than with bone scintigraphy. Patients with history of malignancy In patients with a history of malignancy, careful evaluation is necessary to exclude metastatic disease as the possible cause of low back pain. Cancer of the breast, lung, or prostate often causes spinal bony metastases. Age over 50, unexplained weight loss, and persistent, unrelieved back pain are red flags that metastatic malignancy may be the cause of back pain. 3 Plain films are usually ordered first to determine if there are any abnormalities consistent with metastatic disease. Bone scans are more sensitive in detecting metastatic disease than are plain films, and MRI scans are even more sensitive (96%) than bone scans (77%).ll The AHCPR guidelines3 endorse the use of bone, CT, or MRI scans or CT myelogram for evaluation of back pain when spinal tumor is strongly suspected on the basis of the medical history. Counseling patients who request unnecessary imaging Patients often expect that an imaging study will be ordered during an initial visit for back pain. Deyo and DiehP 4 demonstrated that patients who re- VOL 105/ NO 4/ APRIL 1999/ POSTGRADUATE MEDICINE /IMAGING ceived what they perceived to be an adequate explanation for their pain were more satisfied and less likely to want additional diagnostic tests than those who did not. The investigators also found that patients with back pain who received a brief educational intervention (but did not undergo radiography) were equally satisfied with their care as patients who underwent radiography. When there are no red flags in a patient's history, the patient should be informed that the likelihood of a serious underlying condition is low and that imaging studies are appropriate if improvement does not occur as expected. Most patients respond to this approach if they feel they have had a careful evaluation. If a patient remains significantly anxious despite the physician's best efforts to address concerns, plain films may be appropriate to reduce the patient's anxiety and preserve the physician-patient relationship. Conclusion A focused history and physical examination can identify nearly all patients with acute low back pain who can benefit from imaging studies. Most patients, even those with symptoms of nerve root impingement, improve substantially within 4 to 6 weeks of symptom onset and do not recontinued 171 Imaging, continued quire such studies. Clinical judgment is required when deciding whether a single red flag in the patient's history is sufficient to warrant x-ray films and laboratory tests at the initial visit. If multiple red flags are present, plain films and laboratory tests are usually appropriate at the initial visit. Advanced imaging (CT, MRI, or bone scan) should be reserved for patients who fail to improve as expected or for cases in which such imaging is necessary to confirm the diagnosis of a suspected disease. ~m Earn CME credit on the Web. www.postgradmed. com References 1. Wipf JE, Deyo RA. Low back pain. Med Clin North Am 1995;79(2):231-46 2. Schroth WS, Schectman JM, Elinsky EG, et al. Utilization of medical services for the treatment of acute low back pain: conformance with clinical guidelines. J Gen Intem Med 1992;7(5):486-91 3. Acute Low Back Problems Guideline Panel. Agency for Health Care Policy and Research. Acute low back problems in adults: assessment and treatment. 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