Australian Doctor Australian Doctor 7th September 2018 | Page 26

7 SEPTEMBER 2018 australiandoctor. com. au causes that may present with back pain.

Other clinical situations that may warrant investigation

Radicular pain is described as shooting, narrow, quasi-dermatomal, with buttock and / or leg involvement. Radiculopathy involves sensory loss, reduced reflexes and myotomal weakness in a spinal nerve distribution. There is no urgency to perform radiological investigation in these patients as around 40-50 % will experience improvement in symptoms in the first six weeks with conservative management. 2 MRI is indicated if a guided transforaminal injection or surgery is being considered.

Non-mechanical pain is pain that is not related to movement. This feature should prompt clinicians to carefully revisit the history and examination for missed red flags. Close monitoring of these patients is recommended. Consider rheumatological disease in patients aged over 45 with inflammatory features. These include morning stiffness lasting more than 30 minutes, which improves with activity, and peripheral manifestations such as arthritis, uveitis, enthesitis, and rash.

Figure 1 provides a suggested approach to triaging patients to imaging or observant management based on the clinical features and findings.

Figure 1. Algorithm for red flags and radiology.

Major risk factors for cancer * new onset of low back pain with history of cancer

Risk factors for( or signs of) cauda equina syndrome * new urinary retention * faecal incontinence * saddle anaesthesia

Weaker risk factors for cancer * unexplained weight loss * age > 50 years * ESR 100mm / h or above * haemocrit < 30 %

Risk factors for vertebral compression fracture * use of corticosteroids * significant trauma * older age( above 70) * female gender

Immediate imaging( MRI)

Defer MRI after a trial of therapy

Risk factors for spinal infection New onset of low back pain in the presence of risk factors: * fever * history of IV drug use, recent infection or recent invasive procedure * elevated CRP or WBC count * high clinical suspicion in an at-risk patient

Sever neurological deficits * progressive motor weakness * motor deficits at multiple neurological levels

Risk factors for( or signs of) ankylosing spondylitis * morning stiffness that improves with exercise * alternating buttock pain * awakening because of back pain during the second part of the night * younger age( 20-40)

Plain radiography if negative and persistent clinical suspicion, then MRI

Interpreting radiological investigations

Investigation results require careful evaluation and interpretation. The priority is to identify / exclude red flags or lesions requiring surgical intervention. Red flag lesions may precipitate further evaluation at specialist level. Lesions that may require surgical intervention are not always clear-cut, and close correlation between the abnormality and the clinical signs and symptoms is paramount.

Knowing the prevalence of various radiological abnormalities in a normal, asymptomatic population is important( see table 1). 5

Nuclear medicine bone scan is slightly better than CT at predicting facet joints as a nociceptive source. 6 However, joints with increased activity on bone scan are often not the nociceptive source and cold joints may be the major source. Thus the bone scan’ s main purpose is detecting red flag lesions, not identifying the source of pain.

Controlled medial branch blocks are the only reliable method to determine if a facet joint is a major nociceptive source. 6

The prevalence of disc degeneration in individuals with and without back pain has been extensively studied. MRI studies looking at disc signal intensity, reduced disc height and annular tears reveal that these features are only very slightly associated with an increased incidence of low back pain. Overall, degenerative changes on plain X-ray, CT and MRI have a very poor correlation with spinal pain( see figure 2). 2 The author’ s preferred terminology is age-related change, as opposed to degenerative change.

Internal disc disruption needs to be clearly differentiated from age-related changes seen on radiography. Unlike age-related changes, internal disc disruption radiological changes do correlate with low back pain.

Internal disc disruption occurs when there is disruption to the nucleus pulposus, resulting in fissures to the annulus. This results in increased mechanical stress on the annulus, increased inflammatory chemical leak around nociceptors in the outer one-third of the annulus and neo-innervation of the radial fi s s u r e s. 5 This process is a response to injury and has specific radiological changes that distinguish it from‘ degeneration’.

Pressure-controlled CT discography is the gold standard diagnostic tool for internal disc disruption. 6 However, because of its invasive nature and the degree of training required to perform it accurately, it is not commonly performed in Australia.

There are MRI changes to intervertebral

Based on Traeger2 and Bogduk 5

100

Risk factors for( or symptoms of) spinal stenosis in patients who are candidates for surgery * radiating leg pain * older age * pseudoclaudication

90 80 70 60 50

40 30 20 10

discs that have a strong correlation with discography. They are known as Modic type 1 changes( see figure 3) and high intensity zones. Type 1 changes represent inflammatory oedema surrounding the disc. They are associated with disruption and fissuring of the endplate, and the presence of interleukin 6, interleukin 8, and prostaglandin E2. They can resolve, or evolve into type 2 changes( representing marrow ischaemia).

High intensity zones( see figure 4) are

20-39 40-59 60-80

defined as spots of intensely high signal within the posterior annulus of a disc viewed in heavily T2-weighted MRI images. In sagittal images, they represent the appearance of large radial or circumferential fissures.

Conclusion

In most cases of back pain, radiology rarely makes the diagnosis. Needless imaging has a public cost and may involve exposure to ionising radiation. A patient’ s recovery can

Figure 2. Abnormalities on MRI in asymptomatic patients. HNP: herniated nucleus pulposus, disc D: disc desiccation.( left)

0

HNP Bulge Disc D

Figure 3. Modic type 1

Traeger 2 changes at the L4 / 5 disc.

Table 1. Age-specific prevalence estimates of degenerative spine imaging findings in asymptomatic patients *

Imagine finding

Age( years)

20 30 40 50 60 70 80 Disc degeneration 37 % 52 % 68 % 80 % 88 % 93 % 96 % Disc signal loss 17 % 33 % 54 % 73 % 86 % 94 % 97 %

Disc height loss 24 % 34 % 45 % 56 % 67 % 76 % 84 % Disc bulge 30 % 40 % 50 % 60 % 69 % 77 % 84 % Disc protrusion 29 % 31 % 33 % 36 % 38 % 40 % 43 % Annular fissure 19 % 20 % 22 % 23 % 25 % 27 % 29 % Facet degeneration 4 % 9 % 18 % 32 % 50 % 69 % 83 % Spondylolisthesis 3 % 5 % 8 % 14 % 23 % 35 % 50 %

* Prevalence rates estimated with a generalised linear mixed-effects model for the age-specific prevalence estimate( binomial outcome) clustering on study and adjusting for the midpoint of each reported age interval of the study.

Radiologic Clinics of North America 2012 5

Defer imaging after a trial of therapy MRI

Signs and symptoms of radiculopathy in patients who are candidates for surgery or epidural steroid injection * back pain with leg pain in an L4, L5 or S1 nerve root distribution * positive result on straight leg raise * crossed straight leg raise test

Figure 4. High intensity zones, posterior annulus L5 / S1 disc.

also be substantially delayed if they or clinicians interpret benign changes as serious pathology. In addition, there is a high rate of‘ degenerative’( age-related) change on imaging in asymptomatic populations.

A key to rational ordering of spinal radiology is to consider whether‘ red flags’ for spinal pathology are present, or whether the clinical features point to a lesion that warrants prompt surgical intervention. References on request.