Endgames Picture Quiz

A man with back pain

BMJ 2011; 343 doi: https://doi.org/10.1136/bmj.d4132 (Published 20 July 2011) Cite this as: BMJ 2011;343:d4132
  1. B R K Smith, specialist registrar in radiology,
  2. A Shaw, specialist registrar in radiology,
  3. D Howlett, consultant radiologist
  1. 1Eastbourne District General Hospital, East Sussex Hospitals Trust, Eastbourne BN21 2UD, UK
  1. Correspondence to: B R K Smith brksmith{at}doctors.org.uk

A 41 year old man presented to the emergency department with a one week history of severe and worsening lower thoracic back pain. Examination was unremarkable, with no focal neurological signs. His blood tests were normal except for an isolated raised C reactive protein of 21 mg/L (reference range 0-6). Thoracolumbar spine radiographs showed a T11 wedge fracture, which was unchanged from an earlier radiograph taken six weeks previously. This radiograph had been taken after a fall in which he also fractured his left hip, which needed internal fixation. During that admission he was treated for an Escherichia coli urinary tract infection.

At the current presentation he was unable to mobilise and required admission for analgesia. Over the next 48 hours his pain gradually worsened and at day four he developed a fever (39°C). Blood cultures grew E coli. Urgent magnetic resonance imaging of the spine was arranged (fig 1).

Figure1

Fig 1 Sagittal T2 weighted magnetic resonance imaging scan of the thoracolumbar spine without contrast

Questions

  • 1 What are the radiological findings?

  • 2 What is the most likely diagnosis?

  • 3 What additional investigations may be helpful?

  • 4 How should this condition be managed?

Answers

1 What are the radiological findings?

Short answer

The image shows an anterior wedge fracture of T11 (fig 2). There is abnormal high signal within the T10/11 disc space and destruction of the adjacent vertebral endplates with associated angulation of the spine. Soft tissue is projecting posteriorly and causing narrowing of the spinal canal and compression of the distal cord. Oedema is seen within the T10/11 vertebral bodies.

Figure2

Fig 2 Sagittal T2 weighted magnetic resonance imaging scan of the thoracolumbar spine without contrast showing abnormal high signal in the T10/11 disc space with destruction of the adjacent endplates (white arrow). The adjacent vertebrae display marrow oedema, and there is cord compression at this level

Long answer

In the early stages of discitis the plain radiographs may be normal—changes are usually seen two to four weeks after the onset of symptoms. Plain radiography therefore has a limited role in the diagnosis and surveillance of discitis. The earliest sign is a decrease in disc space height, which is caused by intraosseous herniation of the nucleus pulposus into the vertebral body through the weakened endplate. Ill defined endplates may be seen, and there may be evidence of endplate destruction. After prolonged periods endplate sclerosis may be seen as part of the healing process. Chronic discitis can lead to bone fusion.

With the advent of magnetic resonance imaging, computed tomography no longer has a major role in the imaging of discitis, but it can help identify paravertebral inflammatory masses and other causes of back pain. In addition, computed tomography is useful for obtaining image guided biopsies of the affected disc. Some patients are unable to tolerate magnetic resonance imaging or have a contraindication (such as metal implants), and in these instances computed tomography is still used.

Magnetic resonance imaging is highly sensitive and specific in the diagnosis of discitis and can detect early changes long before abnormalities are seen on plain films.1 In the early stages the disc height is preserved but there may be variable intensity signal in the disc space on T2 weighted images because of disc oedema. This will progress to a loss of disc height and enhancement post-contrast. Erosion and destruction of the adjacent endplates may be seen. Marrow intensity is usually decreased (low T1 signal, high T2 signal) because of oedema in the surrounding vertebrae. Post-contrast images can show avid enhancement in the disc space and surrounding area, including vertebral endplate enhancement (fig 3). Epidural soft tissue extension, a paravertebral mass, spinal cord compression, and altered signal within the spinal cord may also be present. Extensive disease can cause erosion of the surrounding vertebrae and collapse. Diffusion weighted magnetic resonance imaging is a useful technique for differentiating between degenerative and infectious endplate pathology.2

Figure3

Fig 3 Sagittal T1 weighted magnetic resonance imaging scan of the thoracolumbar spine taken after intravenous gadolinium contrast showing strong enhancement of the vertebral endplates, disc space, and surrounding area (white arrows)

2 What is the most likely diagnosis?

Short answer

The clinical history and features on magnetic resonance imaging are consistent with a diagnosis of infective discitis. Discitis is an infection or inflammation of the intervertebral disc space or vertebral endplate. The presence of intractable back pain and fever should alert the clinician to the possibility of this condition.

Long answer

Discitis is an infection or inflammation of the intervertebral disc space or vertebral endplate. The infection is usually the result of systemic bacteraemia from a distant septic focus—our patient’s urinary tract infection is the likely source for the subsequent discitis.

Discitis is a rare condition, with an incidence of about one in 100 000 in the Western world. It is more common in males than in females, with a ratio of 2-5:1. The age of onset follows a bimodal distribution, with a peak at 7 years of age and a second peak at 50 years. There is no racial predilection.

In adults, discitis typically presents with a slow and gradual onset of pain and non-specific symptoms. Plain radiographs may remain normal for several weeks. The diagnosis of discitis is often delayed for these reasons. Fever, rigors, and weight loss may be present but are uncommon. In suspected cases, the threshold for early magnetic resonance imaging should be low.

In children the clinical course is much more rapid. Children often present with acute onset of back pain and difficulty with mobilising. Fever is a common symptom.

Discitis is generally the result of haematogenous bacterial spread. The most commonly implicated infections are pneumonias, urinary tract infections, and skin infections. Injecting drug users have a high risk of developing discitis because of direct contamination of the bloodstream. The most common organisms are Staphylococcus aureus, E coli, and Proteus spp. Although less common in the UK, tuberculosis must always be considered as a cause of discitis, and it can affect multiple disc levels.3 In injecting drug users and immunocompromised patients Pseudomonas is commonly implicated. Another important cause of discitis is recent spinal surgery; the bacterial profile in these cases is different and includes Staphylococcus epidermidis and Streptococcus spp.

Unexplained back pain can be difficult to manage. When evaluating back pain look for “red flag” symptoms and signs, which can indicate serious underlying pathology.4 Red flags include age under 20 or over 55 years at first onset of back pain; trauma; constant or worsening pain; pain that causes the patient to wake at night; weight loss; neurological deficit; steroid treatment; HIV; history of cancer.

3 What additional investigations may be helpful?

Short answer

Magnetic resonance imaging with contrast imaging is the most sensitive and specific test for discitis (fig 3). This can be supplemented with disc space biopsy (either needle or open), which can help confirm the diagnosis if the clinical or imaging findings are equivocal.

Long answer

Even in the presence of convincing radiological evidence of infective discitis, a specific microbiological diagnosis should be sought to enable targeted long term antimicrobial treatment.5 Peripheral blood cultures may help but are not always fruitful. Disc space biopsy is the most sensitive technique for obtaining an accurate microbiological diagnosis. Biopsy cultures are positive in as many as 92% of patients who have discitis, with Staphylococcus aureus being the most common organism.6 The sensitivity and specificity of disc biopsy have been cited at 72% and 94%, respectively.7

If the magnetic resonance imaging findings are typical, the blood cultures are positive, and the patient has no neurological symptoms a disc biopsy may not be needed and treatment can be based on the peripheral blood culture results.8

4 How should this condition be managed?

Short answer

The mainstay of management of infective discitis is a prolonged course of targeted antimicrobial treatment, usually given intravenously. This can be supplemented by surgical debridement if necessary.

Long answer

In the early stages of the disease immobilisation of the patient plays an important role in allowing anatomically aligned fusion of the affected vertebrae. It is common to advise bed rest for two to three weeks at least. After this, spinal bracing devices are often used to immobilise the spine for up to six months.

The mainstay of treatment is antimicrobial drugs. These are usually given intravenously for a prolonged course of at least six to eight weeks, and often much longer. In the absence of positive cultures, broad spectrum antibiotics are given, but otherwise targeted treatment is the norm. Inflammatory markers, including C reactive protein and erythrocyte sedimentation rate, should be monitored throughout. Although erythrocyte sedimentation rate was traditionally the marker of choice for monitoring discitis, several studies have suggested that serial C reactive protein measurements may be more useful. In particular, C reactive protein increases more acutely at the onset of discitis and normalises more quickly after successful treatment.9 10 Nevertheless, recommendations on criteria for ending treatment still include observing a roughly 50% reduction in erythrocyte sedimentation rate and the absence of a neurological deficit.11 12 No benefit has been shown for the routine use of oral antibiotics after the intravenous course.

Surgery for discitis is usually reserved for patients with one or more of the following:

  • Negative blood cultures (percutaneous disc biopsy generally indicated)

  • Neurological impairment

  • Extradural abscesses (which can cause neurological deficit)

  • Progressive spinal deformity (patients should be closely monitored for this)

  • Failure of medical treatment, or uncertainty in the diagnosis of infection.

The surgical procedure generally involves thorough debridement of the affected area. The surgeon has the option to provide surgical fusion at this time, which may help expedite the recovery process but can lead to further complications. Extradural abscesses may need drainage and laminectomy. Progressive spinal deformities can be managed with a spinal stabilisation procedure.

Most patients are cured by surgery—only 15% are left with a residual neurological deficit. The recurrence rate is 5-10%.8 One of the main tools for patient follow-up is monitoring of the erythrocyte sedimentation rate. Radiological evaluation does have a role, but imaging findings often lag a long way behind the active clinical state.

Patient outcome

The patient’s blood cultures grew E coli. After an eight week course of targeted intravenous antibiotics given through a peripherally inserted central catheter the symptoms gradually settled and the patient can now mobilise normally. He has a small amount of residual back pain, but no neurological deficit.

Notes

Cite this as: BMJ 2011;343:d4132

Footnotes

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Provenance and peer review: Not commissioned; externally peer reviewed.

  • Patient consent obtained.

References

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