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Article Excerpt
After completing this article, the reader should be able to:
* Describe the anatomy of the spine and explain why precise diagnosis of back pain is difficult.
* Summarize some of the ways in which psychosocial factors might influence back pain.
* Discuss which imaging studies are used to assist in diagnosis and what drawbacks exist to imaging in the absence of red flags.
* Address special considerations in imaging back pain patients.
* Explain different treatment options, including complementary treatments.
Back pain in its varied presentations is notoriously difficult to diagnose, and descriptions of diagnostic errors unfortunately abound. Imaging plays an increasing role in helping physicians pinpoint the cause of back pain, determine what treatments might be most appropriate and gain a better understanding of the processes underlying this all-too-common phenomenon.
About 10% of adults suffer from chronic pain, and back pain is the leading cause of chronic pain. Chronic pain predictably reduces the quality of life, increases anxiety and depression and now is associated with cognitive and morphological brain abnormalities. (1) Some researchers claim that the proportion of patients whose chronic low back pain (LBP) cannot be diagnosed properly would be reduced by as much as 50% if the potential of modern diagnostic techniques (ie, imaging) were recognized. (2) Imaging also is used to explore brain activity associated with pain, assisting scientists in obtaining a new understanding of the physiological changes associated with pain.
Still, obtaining an accurate diagnosis can be a long process. In 1 instance, a 71-year-old woman was referred to neurosurgeons following a history of LBP that had lasted for more than 10 years. (3) At first, as is typical practice, the woman's general practitioner attributed the back pain to a mechanical cause and recommended conservative treatment that resulted in some level of improvement. After 5 years, however, the pain worsened, and several other diagnoses were proposed, including arthritis, muscle strain and even psychosomatic pain. A full 10 years into the saga, the patient began to experience radiating pain near her knee, numbness and a decreased knee jerk. A neurological examination was otherwise normal, and lumbar-spine radiography showed only expected arthritic changes. Finally, magnetic resonance (MR) imaging permitted physicians to see a mass attached to a nerve root in the lumbar spine. Once the mass was removed, the patient experienced complete relief of her long-term symptoms. It had taken more than 10 years to achieve an accurate diagnosis and obtain true relief of her pain.
Sometimes, pain does not prompt diagnosis and treatment. In another case, a 29-year-old man who had no pain simply went for a Chinese massage, during which a mass was palpated in his right lower abdomen. Although he did not demonstrate any neurological impairment, an MR scan showed a large mass ventral to the spinal column (see Figure 1). The benign tumor was removed surgically without any adverse consequences. (4)
How Common Is Back Pain?
The only neurological complaint more common than back pain is headache. (5) Back problems are recurrent--rarely do they go away and stay away. (6) Between 5% and 10% of patients will develop chronic back pain. (7) Back pain generally is characterized as LBP or other, less common forms of back pain. With respect to acute LBP, the annual consultation rate is at least 35 per 1000 adults. (8) Americans spend more than $50 billion each year on LBP, which is the most common cause of job-related disability and a major contributor to missed work. (5) The American Academy of Orthopaedic Surgeons reported that back pain leads to nearly 12 million visits to physicians' offices each year and that 80% of the population will at some time experience some form of back pain. (9) Other estimates place the figure even higher, predicting that up to 95% of Americans will experience back pain during the course of their lifetimes. (10) Approximately 15% of all adults have recurring LBP, and at least 5% become disabled due to LBE. (11) In 1998, total expenditures associated with back pain in the United States were reported to be more than $90 billion. (12) In 2003, the most recent year data are available, that figure was reported to be a full $10 billion higher. (13)
Americans have not cornered the market on back pain. In the United Kingdom, direct costs associated with disability due to LBP in 1998 were estimated at around 1.6 billion [pounds sterling] per year, with approximately 120 million work days lost. (14) At least once a year, a full 7% of the UK adult population consults a physician regarding LBP. (15) Researchers claim that more than 70% of people in developed countries will experience LBP at some point. (7) In the Netherlands, the costs to society of LBP have been estimated to be 1.7% of the gross national product, with 64% of those costs attributed to absenteeism from work. (16)
Much of back pain can be attributed to lifestyle choices: obesity, sedentary work and home environments and lack of consistent exercise. For some, including health care workers, back pain may be an occupational risk. Given the inherent costs to society, some argue that back pain should be demedicalized and in the absence of clear pathology and red flags indicating probable complications patients should be referred for physical therapy and prescribed exercise programs. (8) That argument might be bolstered by the results of some studies that have shown that about 90% of patients with LBP will have stopped conulting their primary care physician within 3 months. (17)
[FIGURE 1 OMITTED]
Early and accurate diagnosis of back pain and targeting appropriate treatment will reduce patient suffering and the medical and work-related costs of back pain. Diagnostic accuracy is essential for effective treatment. With respect to disk pain, pain patterns provide minimal diagnostic information, and the practice of diagnosing back pain based solely on patients' pain maps or drawings has been shown to have little real success. (2) Rarely can physical examinations distinguish between pain caused by a disk problem and some other cause. In children and adolescents, it is essential to rule out an organic etiology as a cause of back pain. (18) Thus, imaging has an important role to play in refining diagnoses and choosing a treatment. This article focuses on when and how imaging can contribute to a better solution to the problem of back pain.
Anatomy of the Back
Back pain is difficult to diagnose, largely due to the back's complex anatomical structure. It is composed of bone, muscle, ligaments, tendons and a network of neurological components. (19) The spine, or spinal column, which is made up of more than 30 vertebrae, supports the weight of the upper body and surrounds and protects the spinal cord. (5) More than 50 nerve roots enter and exit the spinal cord through spaces between the vertebrae; the intervertebral spaces are maintained by circular, spongy pads of cartilage known as intervertebral disks. (5) These cushioning disks allow flexibility in the lower back and act as a form of shock absorber. Facet joints are the places on each vertebra where the bone articulates with another vertebra, rib or both. (10,20) In the lower back, facet joints carry from 10% to 15% of the compressive load. (10) Ligaments and tendons hold the vertebrae in place and attach muscles to the spinal column.
[FIGURE 2 OMITTED]
The vertebrae are divided into 4 sections: There are 7 cervical (neck) vertebrae (C1-7), 12 thoracic (upper back) vertebrae (Tl-12), 5 lumbar (lower back) vertebrae (L1-5), and a group of bones fused together at the base of the spine known as the sacrum and coccyx (see Figure 2). (5) When the anatomical structure of the spine is altered so that the various parts cannot interact properly, dysfunction results and pain can occur. Predictably, most back pain is found in the lumbar area, which is responsible for supporting the majority of the upper body's weight. This is also the area of the spine that exhibits the most movement. Lumbar spinal motion is quite varied: The healthy lumbar spine flexes, extends, bends laterally and rotates on its axis. (10)
The lumbar disks are composed of:
* An outer rim or annulus fibrosus, which is made up of fibrous tissue.
* The core or nucleus pulposus. A healthy core is approximately 70% water.
* The top and bottom of the disk, also known as the cartilaginous end plates, which are the portions that rest against the neighboring vertebrae. (21)
Disks are the largest structures without a vascular system in the body. Blood vessels lie on the surface only, and so they obtain nutrition from diffusion through the end plates. In addition, disks are only minimally innervated; nerve endings are found only on the surface of the disk. (21)
Disks are designed with crisscrossing fibers that permit them to withstand twisting and other dynamic loads, but they still can tear and cause "discogenic" pain. Lumbar disk herniations are one of the most common diagnoses, and there is significant controversy concerning what treatment is most appropriate for herniated disks. When a disk becomes herniated, either the core or the outer rim of the disk protrudes through its confining membrane. (20) Sometimes these bulges impinge on nerve roots, resulting in pain. Often, however, they are asymptomatic. (21)
The Varied Faces of Pain
Dorland's Medical Dictionary defines pain as "a more or less localized sensation of discomfort, distress, or agony, resulting from the stimulation of specialized nerve endings. It serves as a protective mechanism insofar as it induces the sufferer to remove or withdraw from the source." (20)
Pain teaches us not to touch a hot stove, tells us when we should stop running and sends us to the doctor's office for explanation and relief. Learning from painful experiences also can enhance chances of survival. Pain control--largely approached in Western medicine through the use of pharmaceuticals--has become an area of medical specialty, yet consistent relief of this "symptom" is often elusive:
In the 21st century, it is ironic that although we have made significant advances in our understanding of how pain affects the nervous system and continue to develop innovative treatments, many pain sufferers, including dying cancer patients, receive little or no treatment. One possible explanation is the dizzying development of scientific theories of pain physiology, including the different subtypes of pain and the associated improvements in available treatment options, counterbalanced by increasing regulatory scrutiny and limited financial resources for some patients. (22)
Further complicating the picture, studies show that people experience pain differently; there are varying responses to pain in different ethnic groups and, in turn, varying responses to treatment. (23) Pain responses to stimuli understandably differ. The annoying paper cut results in a dramatically different pain response than does, for example, a broken leg, cancer or pain experienced by heart attack victims. Moreover, pain is impossible to measure objectively: Patients with the same diagnosis and profile might rate their pain on a scale of 1 to 10 and come up with very different numbers. Although the intricate, complicated knot of factors that determines how pain is experienced and reported can render the accurate diagnosis of back pain extremely problematic, imaging is making significant contributions to the understanding of pain and pain behavior.
Traditionally, back pain has been viewed as resulting from some mechanical cause: compression of a nerve or some form of nerve dysfunction. (24) Back pain generally begins after injury or trauma, but it also can be due to degenerative conditions such as arthritis, bone disease, viral infections, irritation to joints or disks and congenital abnormalities. Factors that can contribute to LBP include obesity, smoking, stress, poor physical condition, pregnancy weight gain and poor posture during waking or sleeping hours. (5) Fatigue can increase pain. (25)
Newer approaches to studying the genesis of back pain view the problem on a more minute level, including analysis of immunobiologic and cellular mechanisms. (24) Scientists are continuing to refine their understanding of the underlying cause of back pain as a form of inflammatory process, and studies now focus not only on the vascularization of tissue but also on the types of inflammatory cells found in involved tissue. (24)
Pain can be acute or chronic. Acute pain, such as that suffered by people with appendicitis, serves a clear function: It alerts, warns and provides good indicators as to causation. (22) Acute pain is of short duration and usually subsides once the injury is healed or the problem is resolved. (7) Acute back pain can result from lumbar strain or sprain or from a fracture such as an osteoporotic fracture. (26) Chronic pain, generally defined as pain that lasts longer than 12 weeks, does not serve the same sort of "useful" purpose. Pain that recurs frequently or that lasts beyond the normal healing period also is categorized as chronic pain. (7) Examples of subacute or chronic back conditions include degenerative disk and joint disease, malignancy, fibromyalgia and Parkinson disease. (26) A fundamental step in making an accurate diagnosis is determining whether pain is chronic or acute.
The longer chronic LBP persists, the less the chance of avoiding disability. (17) Many factors appear to determine whether acute back pain will evolve into chronic pain. Some of the factors that contribute to chronic pain include age, physical fitness level, smoking, obesity, low educational level, stress, anxiety, negative moods or emotions, attitudes and beliefs and job dissatisfaction. (16,17) Functional MR (fMR) studies of brain activity connected with chronic pain demonstrate that chronic back pain, no matter what the initial causation, presents a well-defined set of abnormalities. (1) Disconcerting results of fMR studies also reveal a specific pattern of brain chemical changes consistent with decreased gray matter density, which is associated with decreased ability in emotional decision making. (1)
Even more minute changes in brain functioning have been discovered in the brains of people suffering from chronic LBP. Diffusion tensor imaging, which tracks the transport of water molecules in brain tissue, has identified significant alterations in the microstructure of the brain processing centers in these patients. These findings confirm that some effects of chronic pain are a reduction in the plasticity of the brain and flooding of the brain's pain centers with signals. (27)
Magnetic resonance spectroscopy (MRS) can detect biochemical changes, such as pain, that are associated with brain abnormalities. (28) In 1 study, researchers using MRS to analyze biochemical changes in 3 areas of the brain were able to distinguish subjects suffering from LBP from a control group with accuracies of 97% to 100%. (28) Scientists hope that such studies will, in the future, permit development of "brain biochemical fingerprints" of different pain states and that such fingerprints will help physicians choose the most appropriate and effective treatment.
Back pain can be divided into 3 categories: systemic, nonsystemic or osteoporotic (see Table 1). (29) Systemic causes of back pain include tumors, infection and referred pain from causes such as abdominal aortic aneurysms. Systemic back pain demands immediate attention.
Table 1 Types of Back Pain (29) Systemic * Pain patterns are distinctive. * Includes tumors, infections of the vertebrae or intervertebral spaces. * May be due to visceral problems such as intra-abdominal infections aortic or aneurysms. * Pain is usually nonpositional. * Likelihood of cancer increases with patients aged 50 years or older and in patients whose pain has lasted longer than 1 month. * This type of pain qualifies as a red flag and physicians are more likely to order imaging studies early in the course of diagnosis. Nonsystemic * This category of pain is further subdivided into neurogenic and mechanical pain. * Causes of neurogenic pain include spinal stenosis (narrowing of the central or lateral aspect of the lumbar spine, usually with age; ie, arthritis); and sciatica (pain associated with the distribution of the sciatic nerve, usually felt from the buttock down to the foot or in isolated regions of the leg). * Mechanical pain results from a motion or activity that stresses the soft tissues that support the spine (eg, muscles, ligaments, capsules of the facet joints) or that results in disk herniation. The onset of pain is abrupt. In elderly patients, lumbar degenerative disk disease can produce an unstable spine with episodes of acute pain following movement. Osteoporotic * Includes acute vertebral fractures and compression fractures, with pain lasting from 2weeks to 2 months. * Onset of pain is abrupt and intense, may be worse when standing and walking and relieved by lying down.
What Factors Affect How Pain Is Experienced?
Pain has been described as a symphony, in that it is a complex dynamic influenced by pain sensors (physiological), hormones (chemical), emotions and memory. Current research indicates that men and women might use different circuitry to modulate pain. Pain reactions are also highly individualized. In an experiment in which participants' jaw muscles were injected with salt water to simulate temporo-mandibular joint pain, positron emission tomography (PET) brain scans confirmed the differences in participants' pain responses. (13)
Many current studies of the pain process focus on the mind-body connection, looking in particular at the impact emotions have on how pain is experienced and on whether it develops into chronic pain. Studies have consistently demonstrated that the way in which patients handle their emotions (primarily stress) can affect their physical health. In particular, anger and innate hostility have been...
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