Introduction to Imaging
Medical imaging is a frequently used tool by medical and allied health professionals. In certain circumstances, it forms a vital part of the effective investigation of lower back pain. However, in other instances it can add unnecessary expense, delay commencement of care, and even at times cause harm. Like many clinical decisions, the use of imaging in lower back pain is not simple.
Within this article I am aim to outline:
- What medical imaging is
- When it may be necessary
- When it is not necessary
- What is “normal” in medical imaging
- The risks associated with imaging
01. What is medical imaging?
Medical imaging refers to all types of diagnostic imaging used in the investigation of medical presentations. In the case of the lower back, this would commonly include x ray, CT (Computed tomography), MRI (Magnetic Resonance Imaging), or Bone scan (Bone Scintigraphy). A full discussion of the pros and cons of each of these modalities beyond the scope of this article, but each the these modalities have their relative costs and benefits. The most appropriate imaging type is driven by the suspected condition being investigated. As an example, CT is often recognised as the gold standard in accessing for fracture, however if someone is presenting with a suspected disc, or nerve root injury, then MRI is a better choice. The take away here is that it is not a case of one size fits all, and the choice of modality should be driven by a patient’s clinical presentation.
02. When medical imaging may be necessary
Lower back pain is very common. It has been shown that approximately 80% of people will suffer from lower back pain at some stage in their life. In most instances, this pain will resolve. Critically, the management and care in these cases would not be changed by the use of imaging. I will refer to presentations such as this as simple lower back pain. However there are instances of not so simple lower back pain, in which imaging may be necessary.
During an examination of a patient presenting with lower back pain, clinicians aim to identify what are called Red Flags. Red Flags are simply assessment findings that are suggestive of the potential for not so simple lower back pain. If found during the examination the use of appropriate medical imaging may well be necessary.
Examples of red flags in assessing lower back pain include:
- a history of cancer
- unexplained weight loss
- unexplained lethargy or fatigue
- signs or symptoms of infection
- signs or symptoms of immunosuppression
- a history of IV drug use
- history or corticosteroid use
- changes in bowel or bladder function
- acute or progressive changes in strength
- acute or progressive changes in sensation
- changes in reflexes
- failure to improve with conservative management.
03. When medical imaging is not necessary
In the absence of any clinical red flags, imaging is generally accepted as not necessary. For patients, this should be viewed as a positive outcome following a clinical exam, as essentially it indicates that it is unlikely that you are suffering from more serious (not so simple) lower back pain. I have often had patients ask “why not just do it anyway”, or “can we do an MRI anyway” and for someone in pain, and looking to understand why, this at face value is not an unreasonable request.
So why not just do it anyway? Well there are a number 0f good reasons not to image in cases of simple lower back pain. These reasons include:
- Cost to the patient
- Cost to the heath care system
- Delay in commencing care
- Potential exposure to radiation
- Increasing patient fear
- Pathologising normal findings (see the next section for a further explanation of this)
0.4 What is “normal” in medical imaging
Most of these points are pretty simple to understand, but the concept of pathologising normal findings is worth discussing further. Medical imaging is highly sensitive and demonstrates changes in most people. In fact, in the majority of people with no pain, imaging will show structural changes. The following table is taken from a research paper completed in 2014 by Brinjikji et al titled “Systematic literature review of imaging features of spinal degeneration in asymptomatic populations”.
What we see in this is that with increasing age, increasing changes are evident, however again these people are not experiencing pain. Now take the scenario in which a person with asymptomatic changes, starts to develop back pain, and an MRI or CT Scan is completed. The risk is that the person, or the treating health professional will falsely ascribe their pain to these changes. Changes which, were present prior to the onset of pain, and will likely remain evident following its resolution. The challenge as a clinician is too have imaging inform, not make the diagnosis. Treatment based on imaging alone has the potential to increase the use of invasive, or surgical intervention aimed at restoring “normal” anatomy.
05. The risks associated with imaging
Beyond the ability of treatments based on imaging to misdirect management, a number of risks are present with imaging. These risks include exposure to radiation in the case of x-ray and CT, reaction to contrast if used in CT and MRI and increasing fear and stress for patients. Moreover the cost, time delay, and failure to commence care while waiting on imaging can all lead to less optimal patient outcomes.
The use of imaging can be an important part of investigating not so simple lower back pain. However in cases of simple lower back pain, use of imaging can delay care, add cost, and expose patients unnecessarily to radiation. As with many clinical decisions, the choice of whether to image or not needs to balance the relative risks and benefits and based on the patient specific presentation.