Deciphering Chronic Low Back Pain

Research reveals a multifaceted condition for which invasive treatments don’t measure up. Image credit: lightwise/123RF Stock Photo.

Research reveals a multifaceted condition for which invasive treatments don’t measure up. Image credit: lightwise/123RF Stock Photo.

About 80% of us will experience low back pain at some point in our lives. For some, the pain is a constant and dull aching sensation, while for others it’s a sharp shooting pain that comes on suddenly and can be completely incapacitating. The consequences of low back pain extend well beyond the pain itself—it’s the most common cause of disability among people under the age of 45, accounts for one-quarter of lost work days, and costs the U.S. at least $100 billion each year. Low back pain isn’t just a problem in developed countries. It is responsible for more global disability than any other health condition.

For acute low back pain, the prognosis is excellent, and most people find relief in a few weeks, says Richard Deyo, a back pain researcher at Oregon Health and Science University in Portland, US. However, in about 20% of cases, the pain persists for more than three months and is considered chronic low back pain. The condition can have a variety of physical causes, and leads to changes in the brain as well. Psychosocial factors such as beliefs about pain can also influence the level of pain an individual experiences. For the vast majority of patients with chronic low back pain, research indicates that less invasive treatments like exercise and psychotherapy are much more beneficial than more invasive options like surgery.

Causes of low back pain
In a fraction of patients, back pain is caused by degeneration of the intervertebral discs, whose main functions are to hold the vertebrae together and absorb the shock from spine movements. Disc degeneration is one of the few changes observed in back pain patients that can be seen using X-ray or magnetic resonance imaging (MRI), which makes it easier to study than some of the other culprits of chronic low back pain.

Healthy discs have a gel-like substance inside of them that absorbs shock. As discs start to degenerate, they deflate, making them less able to buffer against motion, explains Laura Stone, a pain researcher at McGill University in Quebec, Canada. As the discs collapse, they begin to compress the spinal nerves that run through them, leading to a painful pinched nerve. Advanced disc degeneration also causes pain when the gel inside the disc leaks out (a herniated disc), leading to bulges that can compress nerves or the spinal cord itself. In addition to back pain, people with disc degeneration can also experience pain that radiates down one or both legs (sciatica).

Stone uses animal models to study disc degeneration. People with disc degeneration have lower levels of a protein called SPARC. Similarly, mice lacking SPARC show accelerated rates of disc degeneration and seem to experience both low back pain as well as spinal and radiating leg pain. Stone and colleagues have also shown that, compared to normal mice, those lacking SPARC have an increased number of nerve fibers supplying the discs and the areas around discs, which may at least partially explain how disc degeneration causes back pain. “We’ve also found that degenerating discs have high levels of a growth factor called NGF [nerve growth factor], which attracts pain-sensing fibers to the area, and that blocking NGF with a drug seems to improve back pain in mice,” says Stone. Anti-NGF therapies are currently in clinical trials for back pain and arthritis. “It’s really exciting because this is a brand new way of treating pain and, in the case of back pain, one of the ways it seems to be working is at the disc,” she added.

Although Stone and other researchers are making progress in understanding how disc degeneration causes back pain, most people with back pain have normal disc function. “In the vast majority of cases of acute or chronic back pain, we can’t actually tell what’s wrong. There isn’t an obvious cause,” said Stone. In general, people with back pain are not able to point to a specific incident that caused their pain. Researchers are divided on exactly where the underlying problem is. Current candidates are the muscles, ligaments, and joints in the back, as well as the spine, spinal cord, and even the brain. “[For most people] chronic low back pain is likely caused by a combination of many things,” said Stone, and problems in one area may lead to trouble in another. For example, in individuals with a worn-out disc or a damaged joint, their muscles will try to compensate, leading to muscle pain. Conversely, a pulled muscle might cause a change in posture, ultimately leading to joint damage and low back pain.

The brain in pain
Although chronic low back pain originates in the back, over time it leads to changes in the brain. This is also true of other chronic pain conditions. In general, people who have experienced chronic pain, including chronic low back pain, have a reduced thickness of gray matter (brain tissue where the cell bodies of neurons are concentrated) in the outermost, folded portion of the brain known as the cerebral cortex. This area is responsible for memory, language, perception, thought, and other forms of consciousness.

“[Although the exact cortical regions affected vary across studies], the consistent finding is that patients [with chronic low back pain] generally have less gray matter in their cortex, and a lot of these changes correlate with the duration and severity of the pain,” says David Seminowicz, a pain researcher at the University of Maryland in Baltimore, US.

To examine whether these changes are reversible, Seminowicz, Stone and colleagues have examined brain anatomy in chronic low back pain patients before and after treatment using magnetic resonance imagining (MRI). Before treatment, patients showed less gray matter in a region of the cortex called the dorsolateral prefrontal cortex (DLPFC) that plays an especially important role in cognitive functioning. Six months after treatment (spine surgery or injection of steroids into the space around the spine), patients who responded to treatment by showing less pain and disability had an increase of gray matter in the DLPFC.

“The less pain patients had after treatment, the more gray matter recovery there was in the DLPFC,” Seminowicz said. The researchers found similar results using a different kind of MRI scan that measures brain activity that occurs when subjects are given a task to complete. The DLPFC showed less activity during a cognitive task in chronic low back pain patients than normal subjects before treatment, but brain activity returned to normal levels following treatment.

“A simple take-home message is that if you remove the pain, the brain starts appearing anatomically more normal and functioning more like the brain of a healthy, pain-free person,” Seminowicz explained.

The mind-body connection
Early research in the pain field started by investigating the biological aspects of pain, but over time researchers began to appreciate that psychological and social factors interact with biology to produce pain. Collectively, this is known as the biopsychosocial model of pain, says Steven George, a pain researcher at the University of Florida in Gainesville, US.

If biological factors were solely to blame for chronic low back pain, the degree of injury would strongly correlate with the amount of pain, but in fact, this correlation is often quite weak, said George. “People need to understand that chronic pain is multidimensional, and that biological factors are just the seed,” he added.

Beliefs, thoughts, and feelings about pain can influence how it feels. For example, being afraid of pain makes it feel more intense. The social context in which people experience pain, such as their healthcare system, work environment, and cultural beliefs about pain can also affect pain perception, George said. In other words, “you can increase or decrease the meaning of the pain depending on the context,” he added.

In a recent study, George and colleagues examined the psychosocial factors that best predict whether or not a person will have recovered from low back pain. Patients answered questionnaires at the beginning of the study and after six months. Patients with poorer scores on a psychosocial screening tool (indicating higher risk for psychological difficulties), more depression symptoms, and higher pain levels at the start of the study were the least likely to report recovery after six months. After six months, those patients who strongly believed that physical and job-associated activities would exacerbate their pain were also less likely to have recovered.

Developing research standards        
Given that so many other factors beyond what is happening in the back itself seem to play a role in chronic low back pain, it’s perhaps not surprising that anatomical characterizations of the back using MRIs and other forms of imaging are not particularly predictive of who will get better and who won’t, Deyo tells RELIEF. For most patients, he cautions against rushing into MRI scans or invasive tests too quickly. For those who don’t have any overt muscle weakness or a history of an underlying disease like cancer, jumping into an imaging test can sometimes lead to unnecessary and unhelpful interventions. “You often see something that looks alarming, but because it’s difficult to be sure exactly what the source of the pain may be, it leads to trying to fix something that may not be the cause of the pain in the first place,” he says.

“Over the last couple of decades, we’ve seen increasingly intense treatments for back pain, and yet disability from back pain has actually gotten worse over that time. It looks like things are going in the wrong direction,” said Deyo, citing several-fold increases in the use of diagnostic imaging, narcotics, and invasive treatments like injections and back surgeries over that time.

In response to these alarming statistics, and in an effort to re-examine the research approach to chronic low back pain, in 2012 the National Institutes of Health (NIH) convened a Task Force on Research Standards for Chronic Low Back Pain, which Deyo co-chaired. “The hope of the Task Force was to improve the quality of research by classifying patients based on characteristics that predict their prognosis,” Deyo says.

In order to determine patient characteristics that best predict recovery, there needs to be a set of research standards for future studies, so that researchers can assemble groups of patients that are more alike and be better able to compare results from one study to the next. “The Task Force was charged with coming up with a minimum set of factors that should be included in any and all future studies of chronic low back pain,” explains Task Force member Partap Khalsa, of the National Center for Complementary and Integrative Health, which is part of the US National Institutes of Health (NIH).

After several years of work, the Task Force published a report in 2014 that provided a set of guidelines about how researchers should define chronic low back pain and measure study outcomes. It also listed the key information that should be collected for each study participant: demographic, social, and psychological characteristics; measures of function; and past medical history including health behaviors such as smoking.

“Establishing research standards is a big step scientifically because it enables researchers to speak a common language [for low back pain research] so they can better communicate findings and advance the field even further,” Khalsa tells RELIEF.

Treating chronic low back pain: what actually works?
When talking about treatments, it’s important to distinguish between acute and chronic low back pain, Deyo says. For acute low back pain, the goal is to minimize pain while natural healing occurs. This is usually accomplished through the application of local heat and nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen.

When acute back pain becomes a persistent problem, it’s time for a different treatment approach. In the past, treatment for chronic low back pain kept patients immobile and on narcotics for long periods of time. It is now recognized that’s not always a good approach, Stone says. Substantial research has demonstrated that recovery is fastest when patients return to their normal lives as soon as possible. “Physical activity is one of the best things you can do if you have low back pain, though of course it’s the last thing you want to do. Bed rest is the worst thing you can do,” she says.

There are a number of steps someone with chronic low back pain can take to feel better. “We now know that there are a range of non-drug approaches all of which seem to provide at least modest benefit,” says Khalsa. As is the case for so many other chronic conditions, there aren’t any cures, but there are many ways to manage the pain, he added.

Mounting evidence demonstrates that the most effective treatments for chronic low back pain, as well as other types of chronic pain, target more than just the physical aspects of the pain, George says. A recent analysis that compiled results from 41 different clinical trials, encompassing nearly 7,000 patients, found that multidisciplinary biopsychosocial rehabilitation—which involved both a physical component such as physical therapy and at least one psychological or social/work-related treatment—was more effective than standard treatment in decreasing pain and disability in patients with chronic low back pain (psychological treatments included forms of cognitive therapy aimed at stress management and pain coping strategies; social/work-related treatments included occupational therapy and training to improve activities of daily living at home and work; and standard treatment was that prescribed by the patient’s physician, and, depending on the study, included treatments like pain medicine, stretching, and surgery). Compared to treatments that only addressed physical factors, multidisciplinary treatment also doubled the chances that patients would return to work within 6-12 months.

“In my mind, the mainstay therapy for chronic low back pain is a combination of supervised physical exercises and cognitive behavioral therapy (CBT),” says Deyo. CBT is a type of psychotherapy that helps patients reframe their problem, address unrealistic expectations about recovery, and reduce their fear of activity. Several clinical trials have shown that this combined CBT plus exercise approach is more effective than exercise programs alone in relieving pain and disability, and in improving quality of life, in patients with chronic low back pain. In addition, a recent analysis that combined results from 21 different clinical trials found that exercise—either alone in or in combination with education—can even prevent low back pain.

Although there is less research on complementary and alternative medicine (CAM) approaches, they also seem to be helpful in reducing chronic low back pain. The three best studied and most widely used CAM therapies are chiropractic care (spinal manipulation), acupuncture, and massage. Yoga can also be beneficial, says Khalsa. Overall, these treatments seem to provide some benefit over standard medical care, although the effects are modest and seem to be short-lived.

Are there any roles for drugs or invasive treatments?
In terms of pharmaceutical treatments, antidepressants are often prescribed not just to treat accompanying depression but also to improve the back pain itself, and older drugs such as tricyclic antidepressants seem to be more effective than newer ones, Deyo says. “It’s often worth a try even in someone who is not depressed,” he added.

There are also a host of more invasive treatments for chronic low back pain, but these are most appropriate for patients with clear anatomical abnormalities such as a degenerated disc and who are experiencing both leg and back pain, Deyo says. For example, epidural steroid injections are given to patients with a herniated disc to decrease nerve inflammation. Clinical trials suggest that while the injections improve function and pain for a few weeks, they do not change long-term outcomes or prevent the need for surgery later on.

Surgery is generally most effective for treating the leg pain, rather than the back pain, associated with a herniated disc. It often provides rapid pain relief, but what most patients don’t realize is that even without surgery, the chances are very good that they will improve over time, though at a slower rate, Deyo says. For example, in one trial, both those who underwent early surgery and those who tried conservative treatment first had similar pain relief after one year, although the relief was achieved faster with surgery. For some patients, the rapid results may be worth the risks of surgery; others would prefer to avoid surgery at all costs.

“Patients really need to be informed about the benefits and risks of both surgical and non-surgical interventions,” so that, together with their doctor, they can make the decision that is right for them, Deyo explains. For the majority of patients whose chronic low back pain does not have a clear anatomical cause, the least invasive treatments are the most effective, he added.

“The good news is that there are a range of things people can do [to improve their chronic low back pain],” says Khalsa. However, “right now, we don’t know which of these options should be tried first, or which of them are going to be best for a given individual,” he says. This is an active area of ongoing research that will hopefully provide answers to these questions in the future, he added.

Allison Marin (Curley), PhD, is a neuroscientist-turned-science writer who resides in Pittsburgh, Pennsylvania, US.