Imaging of Lumbar Degenerative Disc Disease

TY - JOUR

T1 - Imaging of Lumbar Degenerative Disc Disease

AU - Carrino, John A.

AU - Morrison, William B.

N1 - Funding Information: Currently, there are many options available for spine imaging evaluation, which contribute to the quandary of how to use them best. Radiography is typically the first line imaging of the lumbar spine and often is used as a “screening” test, in part because it is readily available, has a rapid acquisition time, and provides a reasonable global assessment. CT is used predominately for trauma, when MRI is not available or contraindicated, or for a specific problem solving application related to osseous integrity. Scintigraphy is useful for a global physiologic assessment. MRI has become the mainstay for advanced imaging of the spine and offers complementary features to radiography so most patients with chronic symptoms will have these 2 imaging modalities. Discography is a provocative examination performed under image guidance, and is most useful for establishing a discogenic pain origin and confirming if there is an anular tear or contained protrusion often as a prelude to intradiscal therapy or fusion. CT myelography is also predominantly used as a preoperative test to provide a “roadmap” to surgical planning. MRI can underestimate root compression caused by degenerative changes in the lateral recess, while conventional and CT myelography are more accurate when using surgery as the reference standard to confirm degenerative root impingement in the lateral recess as the cause of radiculopathy. 33 The role of the scintigraphy in patients with acute low back pain is limited. The bone scan is a moderately sensitive test for detecting the presence of tumor, infection, or occult fractures of the vertebrae but not for specifying the diagnosis. The yield is very low in the presence of normal radiographs and laboratory evaluation, and highest in known malignancy. 34 High-resolution isotope imaging, including SPECT, may localize the source of pain in patients with articular facet osteoarthritis before therapeutic facet injection. 35 Similar scans may be helpful for detecting and localizing the site of painful pseudarthrosis in patients following lumbar spinal fusion. 36 The isotope bone scan remains invaluable when a survey of the entire skeleton is needed. Imaging costs have been cited as a major reason for increases in health care expenditures. Actual cost information for delivering radiology services is difficult to quantify accurately using traditional methods. Activity-based costing focuses on processes that drive cost. By tracing health care activities back to events that generate cost, a more accurate measurement of financial performance is possible. However, this is not available for lumbar spine imaging. Charges by institutions and reimbursements by insurers are not true reflections of cost. However, to gain an appreciation of how imaging modalities are valued by the US government, Medicare global reimbursement (circa 2000) was as follows (in US dollars) (1) radiography ($36), (2) scinitigraphy ($204), (3) CT ($280), (4) discography ($335), (5) myelography ($352), and (6) MRI ($542). These dollar values have to be put into the context of information gained, risk to the patient, and downstream relevance to treatment. The value of information to a provider or a patient, albeit often negative or exclusionary, has not been emphasized but has likely been a substantial driving force. Given the high incidence and prevalence of back symptoms, a reduction in imaging expenditures in this domain is an area that health care payers, health services researchers, and evidenced based medical groups have focused on. Low back pain is most frequently associated with degenerative disc disease. Conversely, imaging reveals asymptomatic disc abnormalities in a substantial proportion of patients. Unfortunately, this is the framework that spine providers must contend with. The basic algorithm for low back pain used by many providers traditionally consisted of initial radiographs, followed by cross-sectional imaging (CT or MR) if the radiographs were not definitive. This paradigm assumes that the different etiologies of back pain are of similar consequence and ignores the fluctuation in symptoms characteristic of many chronic disorders. The high prevalence of abnormal MRI or CT findings in the asymptomatic population also makes this approach problematic. Unfortunately, there is no specific imaging biomarker for discogenic pain. On MRI of the lumbar spine, about one-third of asymptomatic subjects have a substantial abnormality. 37 Many people without back pain have disc bulges or protrusions but not extrusions. Given the high prevalence of these findings and of back pain, the discovery by MRI of bulges or protrusions in people with low back pain may frequently be coincidental. 38 Findings on MRI in asymptomatic people are not predictive of the development or duration of low back pain. In a longitudinal study of initially asymptomatic individuals, a poor correlation was found with the development of back pain and the degree of anatomic abnormality on presymptomatic imaging. 39 There is also evidence that abnormalities should be correlated with age in addition to clinical signs and symptoms before operative treatment is contemplated. In patients younger than 50 years old, disc extrusion and sequestration, nerve root compression, end plate abnormalities, and osteoarthritis of the facet joints are less common and, therefore, may be predictive of low back pain in symptomatic patients. 40 Another difficulty is that for patients with nonspecific low back pain, a precise anatomically based diagnosis is often impossible, which leads to various imprecise diagnoses. Radiography is useful for a specific diagnosis in only a minority of patients. MRI and CT are more sensitive than radiography for the detection of early spinal infections, cancer, herniated discs, and spinal stenosis. The role of imaging in other situations is limited because of the poor association between low back pain symptoms and anatomic findings. 41 In isolation, an imaging finding of disc degeneration may represent part of the aging process and, in the absence of extrusion, is of only modest value in diagnosis or treatment decisions. The most common indication for the use of advanced cross-sectional imaging procedures, such as MRI or CT, is the clinical context of low back pain complicated by radiating pain (radiculopathy, sciatica) or cauda equina syndrome (bilateral leg weakness, urinary retention, saddle anesthesia), usually caused by herniated disc and/or canal stenosis. Some believe that the use of advanced imaging should be reserved only for potential candidates for surgery. The Longitudinal Assessment of Imaging and Disability of the Back (LaidBack) study baseline data analysis highlights that a marker for more significant pathology may be a history of multiple episodes of back pain. 42 Those patients who had 5 or more episodes of previous low back pain were much more likely to have a disc extrusion than those who had never had low back pain. The prevalence of moderate or severe central stenosis or nerve root compromise was also higher in those patients with multiple previous episodes of low back pain. Unlike the other MRI findings, which were linked to aging, disc extrusions and nerve root compromise were not significantly associated with age but were associated with previous low back pain. The 3-year follow-up results from this large cohort of initially asymptomatic patients has been recently presented. The incidence of new low back pain was 60%. Overall, the incidence of new imaging findings was low (2% to 9%), and most patients with new imaging findings had no higher incidence of new back pain or sciatica than those without new findings. However, all subjects with new extrusions, new nerve root compression, or new central stenosis also had new low back pain. Although the number of subjects with new imaging findings is too small to permit definitive conclusions, these results suggest that disc extrusions and nerve root compression are likely important imaging findings regarding low back pain. These results also minimize the clinical importance of imaging findings such as anular tears (HIZ) and disc desiccation (T2 signal loss). 43 The differential diagnosis of back pain includes the broad categories of fracture, degeneration, neoplasm, inflammation (infectious and noninfectious), and neurologic. Some back pain causing etiologies are far more serious, requiring an expedited diagnosis and prompt treatment, but the vast majority of causes do not. The nonlife threatening causes can be treated conservatively for several months before embarking on an imaging work-up. With this paradigm in mind, the fist step is to decide whether the patient has any signs of symptoms that fall into one or more serious strata: (1) fracture, (2) cancer and/or infection, or (3) cauda equina syndrome. These signs and symptoms are often referred to as “red flags.” The natural course of many cases of chronic back pain is to wax and wane regardless of what treatment is applied. For adults younger than 50 years old, with no signs or symptoms of systemic disease, symptomatic therapy without imaging is appropriate. If the patient’s symptoms resolve within 4 to 6 weeks, then they can return to normal activities, and no imaging studies are needed. However, if their symptoms persist despite conservative therapy, then further work-up can be pursued. For patients older than 50 years, or those with “red flags,” radiography and simple laboratory tests can almost completely exclude underlying systemic diseases. Looking for “red flags” indicating cancer or infection is a sensitive method, and the use of biochemical markers (Erythrocyte Sedimentation Rate or C-reactive protein) can be helpful. Advanced imaging should be reserved for those patients considering surgery or those in whom systemic disease is strongly suspected. MRI is recommended over CT when the differential includes spinal stenosis, osteomyelitis, epidural abscess, tumor, or recent fracture. A diagnosis of nonmechanical back pain (eg, ankylosing spondylitis) is made only with a strong clinical suspicion. The classic clinical context of ankylosing spondylitis is a young male, with several months of insidious low back pain that is worse predominantly in the morning and improves with exercise. Physical examination reveals tenderness to palpation over the sacroiliac joint region. Treating these patients conservatively for a short time is thought to be appropriate. Compression fractures are a common and possibly preventable cause of low back pain in the elderly osteoporotic population, and should be suspected in an elderly individual with an acute onset of significant axial back pain possibly caused by a minor trauma or mechanical event. In terms of an algorithmic approach, there are several resources available for the evidenced based practitioner. The American College of Radiology (ACR) has developed clinical practice guidelines using a consensus process intended to direct imagers, referring providers, and patients in making initial decisions about diagnostic imaging and therapeutic techniques. The ACR Appropriateness Criteria rank imaging examinations on an ordinal scale from 1 (least appropriate) to 9 (most appropriate) for diagnosis and treatment of specified medical condition(s). There is a guideline for acute low back pain (lumbosacral pain of less than 3 months duration), with or without radiculopathy, with several variants. The use of the ACR Appropriateness Criteria is free to the noncommercial Internet health care community ( www.acr.org ). The NASS is continuously developing clinical guidelines related to the diagnosis and treatment of spinal disorders. These guidelines are developed as educational tools for multidisciplinary spine care professionals to improve patient care by outlining reasonable information-gathering and decision-making processes used in the treatment of low back pain in adults. Phases I and II provide clinical algorithms on low back pain. Phase III provides Clinical Guidelines for Multidisciplinary Spine Care Specialist ( www.spine.org ). These documents are available for a nominal fee from NASS. The National Guideline Clearinghouse is a public resource for evidence based clinical practice guidelines sponsored by the US Agency for Health Care Research and Quality (formerly the US Agency for Health Care Policy and Research) in partnership with the American Medical Association and the American Association of Health Plans. Information regarding spine imaging and treatments may be found on the website ( www.guideline.gov ), and a subscription service is available. The National Guideline Clearinghouse offers guideline abstracts from ACR, NASS, and other sources, links to full-text and ordering information, comparison use for comparing guidelines side by side, guideline syntheses, and annotated bibliographies. The following is a synopsis of the current trend in evidenced based imaging of the lumbar spine. It is obvious from numerous studies and “expert” panels that the majority of uncomplicated acute low back pain is a benign, self-limited condition that does not warrant imaging studies. It is expected that these patients return to their usual activities within 30 days. The challenge for the health care provider confronted with evaluation of these patients is to distinguish the small segment within this larger population that should obtain imaging because of a more serious condition. Indications of a more complicated status (“red flags”) include recent trauma, unexplained weight loss, unexplained fever, immunosuppression, history of cancer, intravenous drug use, risk factors (eg, corticosteroid use) or documentation of osteoporosis, and older than 70 years. 44 Another medical decision making point is to decide if the patient is having primarily low back symptoms, or whether the pain is sciatic or radicular in nature (ie, mechanical versus neurologic pain). In patients with sciatica, early imaging is unnecessary because many patients will improve with conservative therapy and even severe cases may resolve over time. In patients with prolonged or worsening radicular symptoms, MRI or CT can define the lesion and confirm the site of nerve root compression. For chronic (more than 3 months) primarily low back symptoms, lumbosacral radiograph (anteroposterior and lateral views) is appropriate as the initial imaging test. Additional views may not add substantial diagnostic information. The issue of early MRI as a screening test (reduced protocol) and a replacement to radiography has been studied. 45 Radiographs are frequently used as the initial imaging study for low back pain but are neither sensitive nor specific for many causes of low back pain. Recently developed rapid MRI protocols provide more accurate anatomic information. Furthermore, because of reduced imaging time, rapid MRI costs may approach that of radiography. The Seattle Lumbar Imaging Project (SLIP) is a randomized controlled trial measuring cost-effectiveness from the societal perspective of rapid MRI versus radiography for patients with low back pain. This study has completed the data collection portion and is undergoing analyses. The preliminary results suggest that the extra cost of rapid MRI does not result in improved functional status, and, currently, it should not replace radiography in clinical practice. 46 Also in support of a “minimalist” imaging approach is a randomized, unblinded controlled trial performed in the United Kingdom, showing that radiography of the lumbar spine for primary care patients with low back pain of at least 6 weeks’ duration is not associated with improved patient functioning, severity of pain, or overall health status. 47

PY - 2003/12

Y1 - 2003/12

UR - http://www.scopus.com/inward/record.url?scp=0347628881&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0347628881&partnerID=8YFLogxK

U2 - 10.1053/S1040-7383(03)00070-4

DO - 10.1053/S1040-7383(03)00070-4

M3 - Article

AN - SCOPUS:0347628881

SN - 1040-7383

VL - 15

SP - 361

EP - 383

JO - Seminars in Spine Surgery

JF - Seminars in Spine Surgery

IS - 4

ER -