The Role of Imaging in the Evaluation of Low Back Pain

Mark P. Bowes, PhD

  ^*Medical Writer, Portland, Oregon.
  Address correspondence to: Mark P. Bowes, PhD, Medical Writer, 7135 SE 18th Avenue, Portland, OR 97202. E-mail: mpbowes@gmail.com.

Disclosure Statement: Dr Bowes reports having no financial or advisory relationships with corporate organizations related to this activity.

ABSTRACT

Low back pain is among the most common reasons for physician visits in the United States, and is associated with considerable patient distress, limitation of normal activities, and work-related disability. Back pain may be caused by injury or disease of bone, muscle, nerves, spinal discs, or several other spinal structures, and imaging techniques are often essential in making the correct diagnosis. Back pain may be classified by pain duration, severity, or the underlying pathophysiology of the pain. Injury or degeneration of intervertebral discs—fibrous pads that cushion the vertebrae from one another and that help the spine to distribute and support weight—is a common cause of back pain. Disc pain may occur when a damaged disc compresses nearby nerve roots or from the release of chemical mediators that irritate the surrounding tissues. Many other conditions may also cause back pain, including spinal stenosis (narrowing of the spine), vertebral fractures, cancer, and infection. The routine use of imaging for patients with acute back pain is controversial. Imaging is recommended for patients who have certain high-risk features that suggest the presence of a serious underlying disease process (eg, cancer or a spinal infection). In the absence of these "red flags," imaging is not recommended for patients with back pain within the first 4 weeks. There is little relationship between spine imaging results and pain symptoms in these patients, and most individuals with acute low back pain improve spontaneously with conservative management. Guidelines for the diagnosis and treatment of back pain recommend specific imaging techniques for patients with certain high-risk features, including magnetic resonance imaging for patients with suspected cancer, spinal infection, compression of the spinal roots at the base of the spine, and other conditions involving primarily the soft tissues. Plain radiography is recommended for suspected vertebral compression fractures and ankylosing spondylitis (an inflammatory condition involving the vertebral joints). Imaging techniques are also performed in conjunction with invasive diagnostic procedures or pain treatments (eg, image-guided injection of local anesthetics or steroids). Due to the physical and emotional burden of chronic or severe pain, patients with pain present unique challenges in the imaging facility. An attitude of professionalism and empathy is essential to ensure that patients receive the medical care they need in an effective and efficient manner.

Introduction
ow back pain is the fifth most common reason for all physician visits in the United States.¹ Approximately 60% to 80% of the US population experiences low back pain at some point during the lifespan, with approximately 14% experiencing serious low back pain (ie, pain persisting for more than 2 weeks),² and nearly 8% reporting at least 1 episode of severe acute low back pain.³ Although back pain usually resolves spontaneously within 1 to 4 weeks, approximately 33% of individuals with low back pain continue to have persistent moderate-to-severe pain 1 year later, and approximately 20% of patients with back pain have pain that is severe enough to cause substantial limitations of normal activities.^1,4 Low back pain is the leading cause of work-related disability for individuals under the age of 45.² The longer the patient is away from work due to back pain, the less likely the patient is to ever return to full-time employment.⁵ Timely assessment and treatment of back pain is therefore essential to relieve the patient's pain and distress and to decrease the likelihood of long-term disability. 

Diagnosis of back pain can be challenging because of the large number of bones, muscles, nerves, and other spinal structures that are potential sources of pain.⁶ Imaging of the lower back is a very common procedure for the identification of potential causes of back pain, in planning for invasive therapies (such as spine surgery or the injection of steroids or analgesics into the spine), in evaluating the success of treatment, and in clinical studies of new treatments for back pain. This article provides an overview of the role of imaging in the assessment and treatment of low back pain, including the causes of back pain, guidelines on the role of imaging, common procedures for imaging the lower back, and the role of imaging in invasive treatment strategies.

Pain Mechanisms and Pathways
A complete review of the anatomy and physiology of pain perception is beyond the scope of this article. However, a basic understanding of pain pathways is helpful in appreciating the role of imaging techniques in the diagnosis of pain. At the most basic level, the perception of pain usually occurs when specialized nerve endings that are embedded in tissues throughout the body detect tissue injury or the potential for tissue injury. These nociceptors respond to a variety of specific signals, including heat, cold, vibration, stretch, or the presence of chemical substances that are released from damaged cells.⁷ Information from these nociceptive fibers is relayed along afferent nerve pathways (nerves that convey information from the periphery to the brain or spinal cord) and enters the spinal cord through structures called the dorsal roots, which are adjacent to the spinal cord (Figure 1).⁸ It is important to note that the cell bodies of sensory neurons are actually located within the spinal nerve roots, in a structure called the dorsal root ganglion (plural, dorsal root ganglia) which is adjacent to, but outside of, the spinal cord (Figure 1). There are 2 nerve roots and 2 dorsal root ganglia for every vertebra. In contrast, the cell bodies of motor neurons are located inside the spinal cord itself. At each level of the spinal cord, the sensory and motor nerves travel to an innervate a particular portion of the body (Figure 2).⁹ Thus, in some patients with injury to the spine, the pattern of sensory or motor impairments provides important clues about the location of the injury.

Preliminary processing of incoming pain information is performed by nerve cells that are located entirely within the spinal cord (interneurons), and the pain impulses are then relayed by ascending fiber tracts to various structures within the brain. In addition, there are other nerve pathways that originate within the brain and that descend into the spinal cord. These descending nerve fibers increase or decrease the activity of spinal pain-processing neurons, and provide another mechanism to modulate the transmission of pain information from the periphery to the brain.^8,10

It should be clear from this discussion that pain disorders can arise from problems at many different points in this process. For example, pain might be caused by disease or injury that damages the peripheral tissues, stimulates nociceptors without actually causing tissue damage, or affects the spinal roots, or from abnormal processes within the spinal cord, dysfunction of the brain stem or higher brain centers, or at any of the nerve pathways that connect these different points. Due to the diversity of the potential mechanisms that can cause pain, imaging studies and other objective methods are often essential in making the correct diagnosis. 

Classifying Pain
There are many ways to categorize or classify pain, including pain duration (acute, subacute, or chronic), severity (mild, moderate, or severe), or as cancer pain versus noncancer pain (sometimes referred to as benign pain). A significant obstacle to discussing pain diagnosis and treatment is that terminology is often not used consistently by different physicians or researchers. For example, some clinicians define "chronic" pain as pain that lasts for 6 months or longer, whereas others may define chronic pain as lasting for more than 3 months, or that continues after the acute injury has healed.^1,7,11 Another important challenge is that pain is an entirely subjective, personal experience that is often out of proportion to visible tissue injury. Although imaging techniques and other objective tests are often essential to examine potential pain sources, pain assessment still depends on the patient's self-reported experience of pain and pain-related behaviors, such as moaning, limping, avoiding movement, and so on.¹¹  

It is also essential to understand an important distinction between nociceptive and neuropathic pain. Nociceptive pain is caused by the stimulation of peripheral nociceptors. Nociceptive pain signals tissue injury or potential tissue injury, and lasts until the tissue-damaging stimulus is removed.⁸ Nociceptive pain may be subdivided into 2 additional pain types: somatic pain and visceral pain.⁷

• Somatic pain originates in the skin, muscles, joints, or bones, and is usually well-defined and localized. Superficial somatic pain (eg, pain affecting the skin) is often described as "sharp," "burning," or "prickling," whereas deeper somatic pain may be described as "dull" or "aching." Examples of somatic pain include dental pain, a joint sprain or strain, burn pain, or pain at the site of a surgical incision.
• Visceral pain originates in the internal organs, tends to be more diffuse and poorly localized, and is often described as an "aching" or "squeezing" sensation.⁷ Examples of visceral pain include heart attack, peptic ulcer, ruptured appendix, some cancers, and other causes of internal injury or dysfunction.

In contrast, neuropathic pain is generated by a lesion or other type of abnormal activity within the nervous system and does not depend on the activation of pain receptors in peripheral tissues. Neuropathic pain is often described by patients as "tingling," "burning," "stabbing," or "like an electrical shock." Although some clinicians refer to this type of pain as "neurogenic," this label is considered to be inaccurate by some pain experts because all pain is neurogenic (ie, all pain arises from the activity of the nervous system).⁷ A hallmark of neuropathic pain is that it often persists long after the initial trauma has resolved. Neuropathic pain may be subdivided into several different pain syndromes^7,12:

• Mononeuropathies: Conditions that involve a single isolated nerve. Examples include inflammation of a single spinal nerve root, or pain that originates at the stump of an amputated limb.
• Polyneuropathies: Neuropathic pain conditions that affect 2 or more nerves. Nerve damage caused by diabetes, AIDS, or excessive alcohol consumption may cause polyneuropathy.
• Deafferentation: Deafferentation pain occurs when there is a loss of sensory input from the peripheral tissues to the central nervous system (ie, removal of afferent, or inward-bound, nerve impulses). For example, the loss of sensory input following a limb amputation can cause phantom pain, the continued perception of pain from the amputated limb.
• Complex regional pain syndrome (CRPS): A type of pain that develops following nerve injury, and that generally involves 1 or more limbs. CRPS often presents as burning pain, swelling, changes in limb blood flow or color, sweating, and other sensory and motor disturbances of the affected limb.

It should also be noted that patients often have combinations of various types of pain, and that low back pain may include both nociceptive and neuropathic components. Finally, some experts describe other pain classifications or subtypes, including inflammatory pain (sensitization of pain receptors that occurs after inflammation, during the healing process) and dysfunctional pain (pain that occurs without any identifiable tissue injury or inflammation).⁸

Sources of Low Back Pain
The structure of the spine and the spinal nerves is illustrated in Figure 2.⁹ The spinal column is divided into 31 bony segments, or vertebrae. Each segment is associated with one pair of spinal sensory nerves, which innervate the right and left sides of the body, respectively. As shown in Figure 3,¹³ the spine is subdivided into 4 principal regions (cervical, thoracic, lumbar, and sacral), each of which is composed of varying numbers of vertebrae. Vertebrae are numbered from the proximal end (nearest the head) to the distal end (toward the base of the spinal cord) within each section. For example, the second thoracic vertebra is referred to as T2; the first lumbar vertebra is L1. The lumbar and sacral sections of the spine are joined at the L5/S1 (lumbosacral) joint. At the base of the spinal cord, many spinal nerves converge to form a structure that is said to resemble a horse tail—the cauda equina.

Low back pain is often caused by some kind of underlying structural problem or disease process. Injury or degeneration of the intervertebral disc is among the most common causes of back pain, and many imaging techniques have been developed to assess disc structure and function.¹⁴ These discs are circular, spongy pads that sit between the spinal vertebrae and act to absorb and distribute weight and to cushion the vertebrae from each other. The disc consists of an outer rim (the annulus fibrosus), which is composed of fibrous tissue; an inner core (the nucleus pulposus), which is approximately 70% water and that also contains several chemical substances; and cartilage-rich top and bottom end plates, which rest against the adjacent vertebrae.¹⁵ Nearly all cases of painful herniated discs are at L4/L5 or L5/S1, where approximately 80% to 90% of flexion and extension of the spine occurs.^2,15 Injury or disease of the intervertebral discs can produce back pain in several different ways. When discs rupture, lose their shape, or expand, they may compress nearby nerve roots and cause back and leg pain in the parts of the body where these nerves terminate. Chemical substances within the intervertebral discs may be released when a disc ruptures, and these substances may also cause tissue injury or nerve irritation within adjacent nerve roots or other surrounding tissues.² The outer portion of the intervertebral disc is heavily supplied with nerve endings, and the discs may be internally disrupted and intrinsically painful even without affecting nearby nerve roots. For example, discs may lose their structural integrity and develop radial tears even though they have not yet ruptured. In addition, the disc may become painful when the contents of the inner disc portion come into contact with the nerve fibers that supply the outer disc. Clinical signs and symptoms are usually not sufficient to distinguish painful intervertebral discs from other sources of back pain, and imaging techniques are therefore essential for the evaluation of intervertebral discs.¹⁶

Back pain is also caused by several other structural or mechanical problems, including^1,15:

• Spinal stenosis: A narrowing of the spinal canal that puts pressure on the nerve roots at the base of the spine.
• Radiculopathy: A disease of the nerve roots that can cause pain, abnormal reflexes, and sensory impairments.
• Pain originating at the facet joints, which are places on each vertebra where the bone articulates with another vertebra, with a rib, or with both.
• Ankylosing spondylitis: A disease of the spine that causes inflammation of the joints between the vertebrae; eventually, the vertebrae may fuse together.
• Cauda equina syndrome: A rare but serious medical condition in which the nerve roots at the base of the spine are compressed; may cause permanent sensory and motor impairments, including paralysis and incontinence of the bladder and bowel.
• Vertebral fractures
• Cancer
• Infection
• Other underlying structural causes or disease processes

Guidelines for Imaging Back Pain
Back pain is usually subdivided into acute (pain that is present for up to 4 weeks), subacute (symptoms are present for up to 3 months), and chronic (back pain lasting for more than 3 months).¹ The role of routine imaging in patients with acute low back pain is controversial. Most patients with back pain improve within 4 weeks of conservative management (eg, with over-the-counter pain relievers).¹⁷ In addition, it has been estimated that for as many as 85% of patients with low back pain, it is not possible to identify a clear cause of pain using imaging techniques.¹ 

A recent set of guidelines for the diagnosis and treatment of low back pain was developed by the American College of Physicians (ACP) and the American Pain Society (ASP).¹ The goal of the examination of patients with back pain is to classify patients into one of 3 general groups: back pain associated with radiculopathy; back pain associated with another specific identifiable cause (eg, a tumor or spinal infection); and back pain for which no particular cause may be identified (nonspecific back pain). Patients are evaluated for signs or symptoms suggesting severe or rapidly progressing neurologic deficits, including movement problems that involve more than 1 level of the spine, fecal incontinence or bladder dysfunction, or urinary retention. The ACP/ASP guidelines recommend diagnostic imaging and other objective tests of nerve function for patients with low back pain who have severe or progressing neurologic symptoms, or when the history or symptoms suggest that the patient might have a serious underlying medical problem such as a tumor, infection, or cauda equina syndrome (sometimes referred to as "red flags"; Table).¹⁸ In these cases, imaging will often be ordered as rapidly as possible because treatment delays may result in irreversible loss of function in patients with severe spinal conditions.¹

The guidelines recommend certain imaging approaches for patients who are thought to be at risk of the following conditions:

• Cancer: Magnetic resonance imaging (MRI) is recommended for patients with a history of cancer who have a new onset of low back pain; lumbosacral plain radiography is recommended for individuals with unexplained weight loss, failure to improve after 1 month, or who are over the age of 50. Either plain radiography or MRI is recommended for individuals with more than 1 of these cancer risk factors.
• Vertebral infection: MRI is recommended for the assessment of patients with suspected vertebral infection.
• Cauda equina syndrome: MRI is recommended for patients with features suggestive of cauda equina syndrome, including urinary retention, motor deficits that encompass multiple levels of the spinal cord, fecal incontinence, or "saddle anesthesia" (loss of sensation in the buttocks and perineum).
• Vertebral compression fracture: Lumbosacral plain radiography is recommended for individuals with risk factors for vertebral compression fractures (including older age, history of osteoporosis, or a history of steroid use).
• Ankylosing spondylitis: Risk factors for ankylosing spondylitis include younger age, morning stiffness, improvement in symptoms with exercise, alternating buttock pain, and awakening due to back pain during the second part of the night. Anteroposterior pelvis plain radiography is recommended for these patients.
• Severe/progressive neurologic deficits: MRI is recommended for individuals with severe or progressive weakness or other deficits.
• Herniated disc: ACP/ASP guidelines do not recommend imaging studies for suspected herniated discs unless the pain has been present for at least 1 month. For pain lasting 1 month or longer, MRI is recommended for visualizing the spine.
• Spinal stenosis is suggested by a pattern of radiating leg pain, and is more common among older patients. As with a herniated disc, imaging is generally recommended only when symptoms have persisted for at least 1 month.

The guidelines also recommend that clinicians should not perform routine imaging assessments on individuals with nonspecific low back pain during the first 4 weeks.¹ In the absence of red flags, few patients with acute back pain have serious conditions that require immediate intervention, and most patients will improve with conservative management.¹⁹ Findings on computed tomography (CT) or MRI in patients with nonspecific low back pain are often not very closely related to the patient's actual symptoms. The routine use of plain radiography, CT, or MRI for these patients has not been shown to significantly improve patient outcomes,¹⁹ increases total treatment costs, and is associated with significant potential risks. For example, a typical plain radiograph with 2 views of the lumbar spine exposes the patient to an amount of radiation that is equivalent to undergoing a chest X ray every day for more than 1 year.^1,20 In addition, it is possible for imaging studies to reveal "abnormal" findings that may not be involved in the patient's pain. These findings may cause the patient to be "labeled" with a diagnosis based on anatomy that is not actually the cause of the patient's pain, and may also subject the patient to additional and unnecessary tests or procedures.¹⁹ Finally, the guidelines recommend that patients with suspected radiculopathy or spinal stenosis should only undergo imaging if they are considered potential candidates for surgery or epidural steroid injection. MRI or CT is preferred for these patients because they provide better visualization of spinal discs than a plain radiograph.

Despite the fact that many studies and clinical guidelines have suggested that routine imaging is no better than conservative management for patients with acute or subacute back pain, routine imaging of these patients is still widely used for many reasons, including patient pressure to perform evaluations, the physician's desire to try to identify a specific cause of the pain, or because reimbursement structures favor the use of additional testing.¹⁹

Methods for Imaging Low Back Pain
Many imaging techniques are used in the evaluation of patients with back pain. The various options provide different types of information about the back, and each is associated with its own advantages and limitations.^11,21

Plain radiography is the most commonly used technique for the initial imaging of back pain, especially for patients with pain that is thought to be related to diseases of the bone (eg, fractures, inflammatory bone diseases, or bone tumors). Anteroposterior and lateral views are generally used for the initial assessment of back pain because oblique views are associated with higher levels of radiation exposure, especially to the reproductive organs.¹⁷ For suspected compression fractures, images of the entire spine may be obtained because fractures tend to occur at more than one level.¹⁷ Oblique views are often ordered for the evaluation of spondylolysis, a defect of bone that is associated with vertebral fractures and the loss of proper alignment of the vertebrae.²² Plain radiography is often used for the identification of disc degeneration, including fissures within a disc, narrowing of the joint space, and other alterations of the adjacent vertebrae.¹⁴ However, similar findings are often noted in individuals without back pain, and the procedure requires a considerable amount of radiation exposure.

Computed tomography provides greater resolution of soft tissues than plain radiography, and is useful for evaluating potential sources of back pain such as disc rupture, spinal stenosis, or vertebral fractures. It is more widely available than MRI, may be performed in patients with metallic implants who are not candidates for MRI, provides high resolution, and may be performed quickly. CT scans are superior to MRI for the assessment of cortical bone, which is the dense outer layer of bone that makes up the spinal vertebrae.¹⁷ CT is also a useful alternative for patients who cannot tolerate the enclosed space of the MRI apparatus. CT scanners with fast acquisition times have been used to study spinal motion, which can provide important information about spine degeneration and instability. However, the usefulness of CT in the diagnosis of low back pain is often limited because disc changes or other structural abnormalities identified on CT may not be directly related to the patient's back pain. CT scanning is also less able to distinguish soft tissues from one another than an MRI scan, and it is generally less useful for examining the internal structure of the intervertebral discs.¹⁴

Magnetic resonance imaging provides high-resolution images of spinal structures that are often used for the diagnosis of back pain (Figure 4).¹⁴ MRI is especially useful for imaging tumors of the soft tissues, as well as disease or injury of the nerves, muscles, ligaments, and blood vessels. MRI is generally preferred for visualizing spinal stenosis and disc degeneration in patients with chronic back pain, and for evaluating the spinal roots. The addition of gadolinium contrast can help to identify inflammation and infection. T1 and T2 imaging in sagittal and axial planes are standard MRI assessments of the lower back.¹⁶ T2-weighted MRI imaging often identifies dehydrated, degenerated, or ruptured discs, which are sources of low back pain for many patients.¹⁴ Gradient-echo or diffusion-weighted imaging are sometimes used in specific clinical circumstances, such as the assessment of joint inflammation in a patient with ankylosing spondylitis.^23,24 However, as with CT scanning, abnormal findings on MRI are not always the cause of a patient's low back pain, and MRI is usually not performed as an initial step in the diagnosis of low back pain.¹⁷ Disc degeneration or tearing are common findings, and invasive testing is often required to show that the disc changes observed on MRI are in fact related to the patient's pain. A high-intensity T2 signal or bright spot located at the posterior portion of the disc has also been described as a potential diagnostic marker for degenerated intervertebral discs and disc tears (Figure 4), although the association between these high-intensity zones and back pain symptoms is not exact. Other applications of MRI imaging in the evaluation of low back pain include the use of gadolinium chelates to visualize collagen, which is an important component of the intervertebral disc and is crucial to the ability of the disc to bear weight, as well as MRI neurography (high-resolution T2 images to examine changes in the spinal roots), and dynamic imaging to evaluate spine mobility and load-bearing performance.¹⁴ Some experts have suggested that obtaining images while the patient is in the position that normally elicits pain may help to identify lesions that are not evident while the patient is in a neutral posture.²⁵ MRI is often used as the initial imaging method in patients with severe, serious, or progressive neurologic impairments, when a delay in diagnosis might result in significantly worse clinical outcome.¹⁷ It is rarely used for patients with acute back pain unless there is suspicion of a significant underlying disorder, and may be contraindicated in patients with certain metallic implants.

Nuclear bone scans using a variety of radioactive tracers can be used to identify abnormalities of bone metabolism, including tumors, infection, and fractures. Bone scans can also distinguish between new fractures and older fractures that have healed.¹⁷ However, their spatial resolution is generally too low to provide enough information to diagnose other forms of low back pain. Single photon emission CT imaging provides more detailed, 3-dimensional views, and can detect increased metabolic activity in facet joints, vertebral bodies, and discs. It is more time consuming and technically demanding than conventional nuclear imaging.¹⁴

Ultrasound provides less detail than other procedures, but is rapid, widely available, and relatively inexpensive. Ultrasound has been used primarily for research purposes, but has not been extensively applied to the clinical evaluation of back pain.

Invasive Techniques That Employ Imaging of the Lower Back
Image-Guided Injections for the Diagnosis of Back Pain
As noted previously, CT, MRI, or plain radiography often reveal structural abnormalities in both patients with pain and in asymptomatic individuals. Invasive approaches are often needed to relate these anatomic or structural abnormalities to the patient's symptoms.¹⁴ Image-guided spinal injections are used to assess the functioning of anatomic structures that are thought to be important sources of back pain. Injections are used to test the hypothesis that a particular structure is an important source of the patient's pain.⁶ The most commonly identified sites of low back pain include the facet joints, the sacroiliac joints (where the spine joins the pelvis), the intervertebral discs, and the nerve roots. Therefore, invasive imaging techniques are most often used to evaluate these structures. Some commonly used techniques include⁶:

• Selective nerve root injection: Injection of a local anesthetic into a single spinal nerve root under image guidance. If injection of the anesthetic relieves the patient's low back pain, then that spinal nerve root is likely to be a cause of the pain. If the examination of more than 1 level of the spine is required, each level may be tested in a separate test session. In some cases, the same structure may be injected during 2 separate sessions, one using an anesthetic and the other using a saline injection as a placebo, to further verify the structure as a cause of pain. Spinal imaging with CT or fluoroscopy is commonly used to guide needle placement. The addition of a contrast agent may help to determine the spread of the anesthetic through the tissues to ensure that adjacent structures are not inadvertently affected by the anesthetic. MRI may be used when it is desirable to avoid radiation exposure (eg, in younger patients or in those who require many procedures).
• Facet joint or sacroiliac joint injection: Similar to selective nerve root injection, a local anesthetic is injected into the facet or sacroiliac joint. These structures are often sources of low back pain that may be difficult to identify using noninvasive imaging. Relief of pain following anesthetic injection suggests that the target structure is a significant source of back pain.
• Discography: Injection of a contrast dye into a spinal disc that is suspected as the source of back pain. The disc is then imaged using radiography, and the dye helps to identify structural abnormalities. In addition, injection of the contrast agent may reproduce the patient's typical low back pain, either by increasing pressure within the disc, or by directly stimulating nerve endings in or near the disc. The stimulation of the patient's typical back pain during discography provides additional evidence for the involvement of that disc.

Image-Guided Treatment of Back Pain
Image-guided spinal injections are also used to treat low back pain once a source of pain has been identified.⁶ In some cases, therapeutic interventions may be performed at the same time as an invasive diagnostic procedure. For example, once a nerve root, facet joint, or sacroiliac joint has been identified as a source of back pain, the patient may be injected with a steroid to relieve the pain, or with various agents that selectively destroy the nerve roots that are causing pain.⁶

Other Objective Testing
Several other objective studies may help to identify potential causes of back pain. According to ACP/ASP guidelines for the diagnosis and treatment of back pain, the following tests may be considered in the diagnostic workup of patients with back pain¹:

• Erythrocyte sedimentation rate: A blood test for systemic inflammation. May be elevated in patients with cancer, vertebral infection, or ankylosing spondylitis.
• C-reactive protein: Another marker of systemic inflammation that may help to identify vertebral infection or ankylosing spondylitis.
• HLA-B27 antigen test: A blood test for the HLA-B27 antigen, which is a marker that is elevated in some individuals with autoimmune diseases. In patients with back pain, HLA-B27 may help to identify ankylosing spondylitis.
• Electromyography (EMG) and nerve conduction velocity (NCV): These tests measure the electrical activity of muscles (EMG) and nerves (NCV). They are recommended to help diagnose severe or progressive neurologic deficits. They may also be used as part of the workup for patients with herniated discs or spinal stenosis, especially when symptoms have been present for 1 month or longer.  

The Patient with Pain
The evaluation and management of patients with pain can present several significant challenges.¹¹ Patients in pain are often viewed as "difficult" or "problem" patients. Because of the emotional impact of chronic or severe pain, these individuals may be impatient, irritable, rude, or otherwise difficult to interact with. Many healthcare professionals view patients who have pain with a high degree of suspicion due to concerns about malingering (falsely claiming to be in pain), exaggerating pain, or trying to obtain narcotic pain relievers for nonmedical purposes. As noted previously, pain is an entirely subjective phenomenon that is often only loosely related to the extent of visible tissue damage. The perception of pain is influenced by many factors, including activation of pain pathways within the nervous system; the patient's memories, cognitive status, and emotional state; the demands of the particular situation in which pain is experienced; genetic factors; and disease processes.¹⁰ In actual clinical practice malingering, substance abuse, and drug seeking are rarely encountered among patients who are being evaluated or treated for chronic pain.²⁶ An attitude of professionalism and empathy is essential in the evaluation and treatment of patients with pain; expressions of indifference, judgmental or dismissive behaviors, or skeptical comments should be avoided.¹¹ Patients with chronic pain often feel misunderstood or even stigmatized by those around them, including their healthcare providers, and the rate of treatment dissatisfaction among individuals with chronic pain is very high. In some cases, these feelings may cause patients to avoid seeking needed medical care.²⁶

Conclusions
Low back pain is among the most commonly encountered conditions in the imaging facility. In many cases, pain resolves spontaneously with conservative management within 4 weeks. Spine imaging is often essential in identifying the source of pain for patients with high-risk features or when pain does not resolve with conservative management. Most experts do not recommend routing imaging for patients with acute back pain. A variety of imaging techniques are helpful in the diagnosis of low back pain, each of which has its own strengths and limitations. Plain radiographs are often very useful for identifying fractures or other bone disease, but expose the patient to radiation and may provide little information about soft tissue pathology. MRI provides high-definition images of spinal discs and other soft tissues, whereas CT is especially important in evaluating compact bone. Bone scans, ultrasound, discography, and other laboratory techniques are also used in the evaluation of low back pain. Imaging techniques are often used to guide therapy for back pain, including the placement of anesthetic agents or the selective destruction of chronically painful nerve roots. Patients with pain may present unique challenges in the imaging facility; an attitude of professionalism and empathy will help to ensure that these patients are treated as effectively and as efficiently as possible.

References
1. Chou R, Qaseem A, Snow V, et al. Diagnosis and treatment of low back pain: a joint clinical practice guideline from the American College of Physicians and the American Pain Society. Ann Intern Med. 2007;147:478-491.

2. Hills EC. Mechanical low back pain. Available at: http://emedicine.medscape.com/article/310353-overview. Accessed December 9, 2009.

3. Carey TS, Evans AT, Hadler NM, et al. Acute severe low back pain. A population-based study of prevalence and care-seeking. Spine. 1996;21:339-344.

4. Von Korff M, Saunders K. The course of back pain in primary care. Spine. 1996;21:2833-2837.

5. Waddell G. Low back pain: a twentieth century health care enigma. Spine. 1996;21:2820-2825.

6. Fritz J, Niemeyer T, Clasen S, et al. Management of chronic low back pain: rationales, principles, and targets of imaging-guided spinal injections. RadioGraphics. 2007; 27:1751-1771.

7. Koo PJ. The pain continuum: from acute treatment to chronic management. Adv Stud Pharm. 2009;6:94-99.

8. Costigan M, Scholz J, Woolf CJ. Neuropathic pain: a maladaptive response of the nervous system to damage. Annu Rev Neurosci. 2009;32:1-32.

9. www.seer.cancer.gov. National Cancer Institute. Surveillance Epidemiology and End Results. SEER training: spinal cord. Available at: http://training.seer.cancer.gov/brain/tumors/anatomy/spinal.html. Accessed December 9, 2009.

10. Tracey I. Imaging pain. Br J Anaesth. 2008;101:32-39.

11. Furlow B. Pain management imaging. Radiol Technol. 2009;80:447-467.

12. Rho RH, Brewer RP, Lamer TJ, Wilson PR. Complex regional pain syndrome. Mayo Clin Proc. 2002;77:174-180.

13. www.seer.cancer.gov. National Cancer Institute. Surveillance Epidemiology and End Results. SEER training: axial skeleton. Available at: http://training.seer.cancer.gov/anatomy/skeletal/divisions/axial.html. Accessed December 9, 2009.

14. Finch P. Technology Insight: imaging of low back pain. Nat Clin Pract Rheumatol. 2006;2:554-561.

15. Church EJ, Odle TG. Diagnosis and treatment of back pain. Radiol Technol. 2007;79:126-151.

16. Bartynski WS, Petropoulou KA. The MR imaging features and clinical correlates in low back pain-related syndromes. Magn Reson Imaging Clin N Am. 2007;15:137-154.

17. Lateef H, Patel D. What is the role of imaging in acute low back pain? Curr Rev Musculoskelet Med. 2009;2:69-73.

18. Bigos S, Bowyer O, Braen G, et al. Acute low back problems in adults: clinical practice guideline No. 14. AHCPR publication No. 95-0642. Rockville, MD: Agency for Health Care Policy and Research, Public Health Service, US Department of Health and Human Services; 1994.

19. Chou R, Fu R, Carrino JA, Deyo RA. Imaging strategies for low-back pain: systematic review and meta-analysis. Lancet. 2009;373:463-472.

20. Jarvik JG. Imaging of adults with low back pain in the primary care setting. Neuroimaging Clin N Am. 2003;13:293-305.

21. National Institute of Neurologic Disorders and Stroke. Low back pain fact sheet. Available at: http://www.ninds.nih.gov/disorders/backpain/detail_backpain.htm. Accessed December 3, 2009.

22. Mayo Clinic. Spondylolysis. Available at: http://my.clevelandclinic.org/disorders/Back_Pain/hic_Spondylolysis.aspx. Accessed December 9, 2009.

23. Bozgeyik Z, Ozgocmen S, Kocakoc E. Role of diffusion-weighted MRI in the detection of early active sacroiliitis. AJR Am J Roentgenol. 2008;191:980-986.

24. Ojala R, Klemola R, Karppinen J, et al. Sacro-iliac joint arthrography in low back pain: feasibility of MRI guidance. Eur J Radiol. 2001;40:236-239

25. Gilbert JW, Wheeler GR, Lingreen RA, et al. Imaging in the position that causes pain. Surg Neurol. 2008;69:463-465.

26. Canaday BR. Management strategies for frontline pharmacists. Adv Stud Pharm. 2009;6:108-114.