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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 .