Mechanical or inflammatory low back pain. What are the potential signs and symptoms?
From: Manual Therapy Journal. In Press – published online 16 June 2008
Non specific low back pain is commonly conceptualised and managed as being inflammatory and/or mechanical in nature. This study was designed to identify common symptoms or signs that may allow discrimination between inflammatory low back pain and mechanical low back pain. Experienced health professionals from five professions were surveyed using a questionnaire listing 27 signs/symptoms.
Morning pain on waking demonstrated high levels of agreement as an indicator of inflammatory low back pain. Pain when lifting demonstrated high levels of agreement as an indicator of mechanical low back pain. Constant pain, pain that wakes, and stiffness after resting were generally considered as moderate indicators of inflammatory low back pain, while intermittent pain during the day, pain that develops later in the day, pain on standing for a while, with lifting, bending forward a little, on trunk flexion or extension, doing a sit up, when driving long distances, getting out of a chair, and pain on repetitive bending, running, coughing or sneezing were all generally considered as moderate indicators of mechanical low back pain.
This study identified two groups of factors that were generally considered as indicators of inflammatory low back pain or mechanical low back pain. However, none of these factors were thought to strongly discriminate between inflammatory low back pain and mechanical low back pain.
Low back pain is a common problem with point prevalence ranging from 12% to 33%, 1-year prevalence 22–65% and lifetime prevalence 11–84%. While low back pain is usually self-limiting, it can persist resulting in a substantial personal, social and economic burden. In the majority of cases, a specific diagnosis for low back pain cannot be defined on the basis of anatomical or physiological abnormalities. Although imaging strategies can be employed to exclude serious causes of low back pain (such as tumours and infections), anatomical abnormalities, such as those associated with the aging process, are commonly observed in otherwise asymptomatic, healthy individuals. While specific therapies can be employed to correct identifiable anatomical or physiological abnormalities, non-specific low back pain can only be treated empirically.
Systematic reviews have described the benefit of a broad range of physical and pharmacological interventions over natural history or placebo therapies, but have conceded that effect sizes are small, with little difference in outcomes observed when alternative therapies are compared. This apparent lack of effect may, at least in part, be due to the tendency to treat non specific low back pain as a homogenous condition, rather than a heterogeneous collection of as yet undefined but differing conditions, some of which might respond and others that do not respond to a particular therapy.
There is therefore a need to identify subgroups within the broad classification of non specific low back pain, and given the failure of classification on the basis of anatomical and physiological abnormalities, attempts have been made to identify subgroups on the basis of symptoms and physical signs. This syndromic approach has been limited in the past because of the poor inter-rater reliability of proposed classifications. More recently, however, several subgroup classification systems have been demonstrated to have moderate or good inter-rater reliability. Subsequent randomised controlled trials have indicated that patients with non specific low back pain who receive treatment matched to subgroup classifications have better outcomes than those who receive alternative therapies. It therefore seems likely non specific low back pain does represent a heterogeneous collection of conditions and that the identification of subgroups can result in improved outcomes through directed therapies.
non specific low back pain is commonly described as being mechanical or inflammatory. Although these labels have no universally accepted definitions, there is evidence to support the involvement of both mechanical and inflammatory factors in the generation of low back pain. Further, there are two distinct types of treatment for low back pain that seem to follow this nosological separation. That is, mechanical treatments such as mobilisation, manipulation, traction and exercise are contrasted with notionally anti-inflammatory treatments like non-steroidal anti-inflammatory medications and corticosteroid injections. There are studies that examine signs and symptoms of specific inflammatory arthritides of the spine such as ankylosing spondylitis. But once conditions like ankylosing spondylitis have been ruled out there are no studies that determine whether or not inflammatory low back pain and mechanical low back pain subgroups can be differentiated within the non specific low back pain classification.
It would therefore seem useful to attempt to divide low back pain sufferers into groups that may respond more readily to two types of treatment, mechanical or inflammatory. If this were possible the number of inappropriate therapy decisions could be decreased.
The aims of this study were to identify common symptoms or signs that may allow discrimination between inflammatory low back pain and mechanical low back pain and determine whether the different groups involved in the management of low back pain interpret these signs and symptoms in a similar manner.
Although non specific low back pain is commonly described as being mechanical or inflammatory in nature and is treated by mechanical and anti-inflammatory therapies, there have been no previous attempts to distinguish these subgroups on the basis of symptoms or clinical signs. However, Rudwaleit et al. did study the clinical history of 101 ankylosing spondylitis patients and 112 patients without ankylosing spondylitis thereafter labeled as mechanical low back pain patients. In their methods they used an external reference standard known as the New York Criteria to diagnose ankylosing spondylitis. They found four factors that potentially separated the two groups, these were morning stiffness greater than 30min, improvement with exercise but not with rest, awakening because of back pain in the second half of the night and alternating buttock pain. However, despite some similarity in their results, their study differs from ours insofar as they compared a specific inflammatory arthritide (ankylosing spondylitis) with all other cases of back pain which they tagged mechanical low back pain.
In contrast we asked expert respondents to compare non-specific inflammatory low back pain with non-specific mechanical low back pain. In our questionnaire there were no pre-determined definitions or external reference standards (other than exclusions) to categorise non-specific inflammatory low back pain or mechanical low back pain. Indeed this was the reason for our study, to measure the opinion of experts about the extent to which mechanical low back pain and inflammatory low back pain can be distinguished by signs and symptoms.
Our study demonstrated some evidence that a number of signs and symptoms are possible indicators of inflammatory low back pain or mechanical low back pain. However, there was no clear agreement either within or between professions regarding whether statements based on common signs and symptoms of low back pain are either indicative of, or can distinguish between inflammatory or mechanical causes of low back pain.
An ideal statement for inclusion in an instrument that distinguishes between inflammatory low back pain and mechanical low back pain would have a high score for one form of low back pain, a low score for the other form, a significant difference between the scores for both forms and no significant difference between professions with respect to interpretation. None of the studied statements met each of these criteria.
Although morning pain on waking and pain that wakes the person up were thought to be broadly indicative of inflammatory low back pain and pain on lifting was thought to be broadly indicative of mechanical pain, this was not universally recognised either within or between professional groups. Of these, morning pain on waking is commonly used as a marker of pain due to inflammation.
The fact that morning pain is used as a marker of disease severity in inflammatory spondyloarthopathies such as ankylosing spondylitis could explain why several respondents suggested that this marker should have been expanded in our survey to reflect the length of time the pain lasted in the morning.
The relationship between inflammation and pain, however, is not clear. Although a recent study found that the mean intensity of pain over 24h was independently associated with high levels of high sensitivity C reactive protein in patients with acute sciatica (less than 8 weeks), this association was not found in patients with chronic low back pain.
Similarly, the relationship between pain that wakes a patient up and inflammation is not clear. Sleep disturbance is commonly reported in people with non-specific chronic pain, as well as those with inflammatory arthritis. The mechanisms by which pain and inflammation cause sleep disturbance have not, however, been well described and may differ.
Although the levels of inflammatory cytokines, such as interleukin-6 may alter sleep behaviour, there did not appear to be an association between improvements in pain and joint stiffness, and improvements in sleep disturbance, in a small group of patients being treated for rheumatoid arthritis with non-steroidal anti-inflammatory drugs.
Although pain on lifting is commonly thought to represent mechanical pain, the relationship between spinal load and pain is not clear. Whilst there is strong evidence that work activities such as lifting, bending, twisting and vibration are a risk factor for the onset and reporting of non specific low back pain, overall it appears that the size of the effect is less than that of other individual factors. It is postulated that load, posture and creep may alter the mechanical properties of the spine, resulting in stress concentration in innervated tissues such as the intervertebral discs, facet joints and ligaments, but there is little direct evidence that such factors are important in non specific low back pain. In overview the results could be interpreted to suggest that movement or activity-related symptoms are more broadly indicative of mechanical low back pain and that pain at rest is more indicative of inflammatory low back pain.
Interestingly no variable was considered to represent both inflammatory low back pain and mechanical low back pain and using our analysis, 10 variables were not considered indicative of either inflammatory low back pain or mechanical low back pain.
While it is possible that varying educational paradigms could explain variability between professional groups, it does not obviously explain the variability we found within groups. As the key participants (experts) in this study were selected on their academic and professional standing, it is likely that these differences will be transmitted down through the ranks of each profession and sustains the inadequacy of the evidence.
The strength of this study is its good response rate and its generalisability to a wide range of practitioners; however, the study does have some limitations. First, the respondents were not randomly selected from within their professional groups, therefore one cannot generalise the results to the entire population of professionals in each group. However, our purposeful intention was to get the opinion of approximately 20 experts from each group. In this way the answers to our primary questions are more likely to have content validity. Secondly, the best method for defining subgroups within the broad diagnosis of non specific low back pain has not been established.
The approach of this study was to suggest two possible subgroups, inflammatory low back pain and mechanical low back pain and investigate whether experts within relevant professional groups could independently agree on certain symptoms and signs. This approach highlighted the variation within and between participating groups. A similar approach would be to use the Delphi technique (using an iterative/consensus method) to define a set of symptoms and signs that could be measured in trials of mechanical and anti-inflammatory therapies. If symptoms and signs could be used to define subgroups of patients with inflammatory low back pain and mechanical low back pain, trials could be conducted to determine if those who receive subgroup specific treatment do better with the subgroup-specific treatment rather than non-specific treatment, thereby confirming the validity of the subgroups. Despite the limitations of this study, it is clear that considerable diversity of opinion exists regarding symptoms or signs that might be used to distinguish between mechanical low back pain and inflammatory low back pain, both within and between the professional groups involved in the management of non specific low back pain.
non specific low back pain is commonly labelled, conceptualised and managed as being inflammatory and/or mechanical in nature and this study identified two groups of factors that were generally considered as indicators of inflammatory low back pain or mechanical low back pain. However, we identified few, if any, signs or symptoms that members of professions involved in the management of non specific low back pain could highly agree distinguished between these aetiologies. While the general absence of agreement regarding signs and symptoms of inflammatory low back pain and mechanical low back pain does not invalidate the pathophysiological paradigms of mechanical and inflammatory pains, it does, however, signal the need for further research.
This research should be aimed at testing the 17 indicators identified for their ability to predict the outcome of mechanical and anti-inflammatory treatments of low back pain. If further study establishes that they are able to predict the outcome of the two treatment types, the number of inappropriate decisions to use either may be decreased.
