Differentiating Inflammatory and Mechanical Back Pain
Back pain (including neck, thoracic and lumbar pain) is a common presenting condition in physiotherapy practice. Neck and low back pain have been identified as the leading cause of global disability in 2015 in most countries. The lifetime prevalence of low back pain is reported to be 84 percent while the prevalence of chronic low back pain is around 23 percent. Moreover, between 11 and 12 percent of the population are considered disabled by low back pain.
The majority of patients presenting with back pain will be classified as having non-specific mechanical back pain (i.e. pain that is generated by the spine, intervertebral discs and surrounding soft tissue - including muscle strain, disc herniation, lumbar spondylosis, spondylolisthesis, vertebral compression fractures etc). However, it is essential to be able to identify patients who fall outside of this category, including those with back pain of inflammatory origin. This page will highlight some key features that can help to differentiate between mechanical back pain and inflammatory conditions, as well as discussing other red flag features that should always be considered.
When assessing patients with back pain, it is necessary to first consider if there are any red flags present. Only around one percent of all musculoskeletal presentations in primary care will be due to serious pathology (such as spinal infection, cauda equina syndrome, spinal fracture and malignancy). However, as Finucane notes, these conditions should be considered as differential diagnoses when individuals present with back pain - particularly if the patient is not responding in an expected way or is starting to worsen.
Common red flags include:
- Age over 50 years
- Progressive symptoms
- Thoracic pain
- Past history of cancer
- Weight loss
- Drug abuse
- Night pain
- Systemically unwell (fever)
- Night sweats
Other important points to consider include:
- The presence or absence of trauma - could there be a fracture or a risk of osteoporotic fracture?
- Could the pain be referred from visceral organs? An abdominal aortic aneurysm and the kidney can, for instance, both cause low back pain
While targeted towards doctors, the following video provides a summary of key red flags for low back pain.
- For more information on red flags, please click here.
- For more information on spinal malignancy, please click here.
Taking a thorough subjective history is essential to ensure you are able to accurately distinguish between mechanical, inflammatory and other types of back pain. The specific areas that should be included in a subjective assessment are discussed below.
Timeline of Pain
Understanding the timeline of a patient’s pain will help the clinician to gauge whether pain is inflammatory or mechanical. Specific questions that should be included are:
- Was there a recent trauma or is the pain of insidious onset?
- How long has the patient had the pain?
- At what age did his / her pain start?
- Is the pain recurring?
Inflammatory pain would more likely be of insidious onset and of longer duration (i.e. more than three months) whereas mechanical pain tends to be more acute and can often be linked to an injury.
Age at symptom onset is also a very important consideration as spondyloarthropathy occurs in younger adults (i.e. less than 45 years) while other degenerative conditions (such as degenerative disc diseases, facet joint changes or osteoarthritis of the spine) tend to worsen with age.
Aggravating or Easing Factors
Having an understanding of the factors that aggravate or alleviate a patient's back pain can also help you to distinguish between mechanical and inflammatory pain. Important subjective questions to ask include:
- Does pain come on at rest or at night?
- Does pain ease with movement?
An affirmative answer to these questions is indicative of an inflammatory condition as mechanical pain tends to worsen with movement and ease with rest.
24 Hour Pain Pattern
Inflammatory pain will usually have certain characteristics across a 24 hour period. Questions to ask include:
- Do you have night pain?
- Are you waking in the second half of the night?
- Does your pain improve when you first get up in the morning and start moving around?
- Do you have any stiffness associated with your pain that lasts more than 30 minutes?
- NB: mechanical back pain can cause stiffness, but this tends to improve after a few minutes
Positive responses to these questions suggest an inflammatory condition.
A strong genetic component has been identified in spondyloarthropathy. It is, therefore, important in the subjective interview to find out if a patient has a family history of spondyloarthropathy.
Since spondyloarthropathies have other extra-articular manifestations, it is necessary to find out if the patient has any other medical issues, including gut, eye or skin problems.
Similarly, spondyloarthropathies can affect other peripheral joints, tendons and ligaments, so finding out about other musculoskeletal issues can aid in the detection of inflammatory conditions. For instance, it is beneficial to ask if the patient has any enthesitis (e.g. at the heel or achilles tendonopathy, or lateral epicondylalgia). A positive response to these questions can indicate that there is systemic inflammation.
NB: Enthesitis is defined as inflammation of the site where tendons / ligaments insert into bone.
Pain is a complex process and can be influenced by many factors, including motivational, emotional and cognitive states. Rather than just considering the disease state, there is now a general consensus that health and illness result from the interaction between biological, psychological and social factors - i.e. the biopsychosocial model.
Essentially, the biopsychosocial model focuses not on the disease, but on the behaviour that fuels beliefs or attitudes that may perpetuate problems associated with the disease. For instance, one person may experience sensations such as pain, nausea or heart palpitations differently to another. This variation in perception should be considered against the backdrop of the patient's psychological and social context.
The biopsychosocial model is discussed in more detail here and here. However, in terms of differentiating mechanical and inflammatory back pain, it is helpful to gain an understanding of your patient’s social, psychological and biological context. This will enable you to develop a better understanding of the nature of his / her pain.
For more information, on the objective assessment of low back pain, please click here. When differentiating between mechanical and inflammatory back pain in particular, it is useful to assess:
- Gait - is it antalgic or symmetric?
- Posture - does the patient have altered posture, such as a loss of lumbar lordosis or an increase in thoracic kyphosis?
- Chest expansion - does the patient have any restriction in chest expansion?
- Range of motion - is there a reduction in range or stiffness?
- Palpation - is there any tenderness on palpation across the spine and sacroiliac joints?
- Entheses points - is there any pain at these points?
Patients with spondyloarthropathy, particularly axial spondyloarthritis, will often present with pain, stiffness and a loss of motion in the back, as well as abnormal posture, enthesitis, and a restrictive pulmonary pattern due to diminished chest wall expansion and decreased spinal mobility.
As with any assessment, the objective findings may not always be conclusive. A patient may have reasonable range of motion or appear to have normal posture. However, when the objective assessment is considered in conjunction with the subjective assessment, it will be possible to gain a clearer picture of the nature of the patient's pain.
Back pain is a common presentation in clinical practice. While the majority of patients tend to have non-specific mechanical back pain, it is important to consider if there is any indication of inflammatory pain or other red flags.
A thorough subjective and objective assessment will enhance your ability to distinguish between mechanical and inflammatory back pain.
The key differences between mechanical and inflammatory back pain are summarised in the following table:
|Mechanical Back Pain||Inflammatory Back Pain|
|Occurs at any age||Age of onset < 45 years|
|More acute onset||Pain duration > 3 months|
|Onset is variable - may be caused by a specific event||Insidious onset|
|May worsen with movement / exercise||Improves with movement / exercise|
|Improves with rest||Does not improve with rest|
|Little or no morning stiffness||Early morning stiffness which lasts > 30 minutes|
|Pain at night, which may wake the patient|
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