Spinal Infections Workup

Updated: Feb 13, 2018
  • Author: Federico C Vinas, MD; Chief Editor: Jeffrey A Goldstein, MD  more...
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Workup

Approach Considerations

In 2015, the Infectious Diseases Society of America (IDSA) published clinical practice guidelines for the diagnosis of native vertebral osteomyelitis (NVO) in adults (see Guidelines). [37]

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Laboratory Studies

Leukocytosis, the usual indication of infection, is often absent or minimal in patients with chronic pyogenic vertebral osteomyelitis.

Elevation of the erythrocyte sedimentation rate (ESR), though nonspecific, is the most common laboratory abnormality. Back pain coupled with an increased ESR should lead the clinician to suspect vertebral disease such as infection, neoplasia, or rheumatoid disorder.

Blood cultures should always be obtained before administration of antibiotics.

C-reactive protein (CRP), synthesized by hepatocytes, is an excellent indicator of inflammation. Patients with bacterial diskitis have higher serum CRP and fibrin levels. Patients with nonseptic diskitis (ie, chemical diskitis) have only dense fibrotic histologic changes, and serum CRP and fibrin findings are normal.

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Plain Radiography

The process of diagnosing a spinal infection usually begins with a radiograph, though radiographic findings are usually normal in the first 2-4 weeks. If the disk space is involved (diskitis), the disk space may narrow, and destruction of the endplates around the disk may be seen on the radiograph. (See the image below.)

Spinal infections. Lateral plain radiographs of Pa Spinal infections. Lateral plain radiographs of Patient A with diskitis at C4-5. Note the severe disk space narrowing and subluxation seen at C4-5.

Later, plain radiographs usually reveal rarefaction, loss of bony trabeculation close to the cartilaginous plate, and an irregular narrowing of the vertebral disk space. Vertebral body collapse may also be seen (see the image below). Simultaneously, evidence of rapid bone regeneration may be evident, with the development of bone spurs and dense new bone. A paravertebral soft-tissue mass may also be present.

Spinal infections. A 47-year-old woman (Patient B) Spinal infections. A 47-year-old woman (Patient B) who presented with intractable back pain. Radiographs reveal significant collapse and destruction of the L4 vertebral body. An MRI of the lumbar spine was ordered.
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CT and PET

Computed tomography (CT) depicts osteomyelitis earlier than plain films do. CT findings include hypodensity at the site of infected disks, lytic fragmentation of the involved bone, gas within an involved vertebra, and decreased density of adjacent vertebrae and nearby soft tissues. Epidural and paraspinal extension of infection may also be seen.

The use of 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in conjunction with CT is helpful in the diagnosis of vertebral osteomyelitis. In a study by Kouijzer et al, which compared 18F-FDG-PET/CT and MRI with the clinical diagnosis, 18F-FDG-PET/CT had a sensitivity of 100%, a specificity of 83.3%, a positive predictive value of 90.9%, and a negative predictive value of 100% for diagnosing vertebral osteomyelitis. [38] In particular, 18F-FDG-PET/CT had an advantage for visualization of metastatic infection, especially in bacteremic patients.

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Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) of the spine provides information that CT does not. [39]  Characteristic MRI findings include destructive and expansile lesions involving two adjacent vertebrae and their intervening disk.

Low-density changes in bone and disk are seen on T1-weighted images, whereas high-density changes are seen in these structures on T2-weighted images, presumably from their increased water content. Intravenous infusion of gadolinium shows enhancement of the involved structures. Paravertebral infection, collections under the posterior longitudinal ligament, and epidural abscesses may also be shown. (See the images below.)

An MRI of Patient B reveals an enhancing mass affe An MRI of Patient B reveals an enhancing mass affecting the L4 vertebral body with compromise of the spinal canal. The patient underwent several blood cultures and a CT-guided trocar biopsy; culture results were negative. A surgical procedure was necessary.
Spinal infections. T2-weighted MRI of Patient A. E Spinal infections. T2-weighted MRI of Patient A. Evidence of osteomyelitis and diskitis, as well as a small epidural abscess, is present. The patient underwent a C4-5 anterior cervical diskectomy and arthrodesis using autologous iliac crest bone graft and instrumental fixation with a titanium plate and screws.

Diffusion-weighted imaging is useful in distinguishing between degenerative and infectious endplate abnormalities. Compared with positron emission tomography (PET), diffusion-weighted MRI costs less, has faster imaging times, and does not involve the use of ionizing radiation. [40]

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Radionuclide Scanning

Radionuclide scans with technetium-99m are very sensitive early indicators of pyogenic vertebral osteomyelitis. Radionuclide scan findings become positive long before plain film changes are evident.

Technetium-99m bone scanning is not useful for specifically differentiating infection from metastasis or osteoarthritis. Gallium is more likely to localize an inflammatory lesion, and technetium-99m combined with gallium-167 demonstrates virtually all pyogenic vertebral infections. [41]

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Myelography

In the past, myelography was used in the evaluation of vertebral osteomyelitis to delineate areas of epidural spread and neural compression. MRI has largely supplanted myelography because of its ability to depict not only bony changes but also pus and granulation tissue under the posterior longitudinal ligament and epidural infection.

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Other Tests

Urodynamic studies may be helpful. Patients with vertebral osteomyelitis can develop urinary retention. Methods of objectively testing the behavior of the lower urinary tract during filling, storage, and micturition include the following:

  • Uroflowmetry
  • Cystometry
  • Sphincteric electromyography
  • Combined studies

When appropriately used, urodynamic testing provides valuable information for the evaluation and subsequent treatment of neurourologic dysfunction.

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Biopsy

CT-guided percutaneous biopsy of the infected vertebra or disk may be done via a needle or trocar. Findings are positive only 60-70% of the time. This is a minimally invasive test used to obtain histologic confirmation of the disease and tissue samples for culture. Trocar biopsies have proved more useful than fine-needle aspiration (FNA) because they allow a larger amount of material from the infected area to be examined histologically as well as cultured.

As with blood cultures, the likelihood of positive tissue culture findings decreases if antibiotic therapy has already been initiated. A 10-year retrospective review suggested that paravertebral soft tissues may also be considered viable biopsy targets. [42]

If blood cultures and percutaneous biopsy fail to identify the infecting organism, open surgical biopsy is indicated. An open surgical biopsy has the highest yield in terms of positive culture findings and diagnostic confirmation. [43]

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Histologic Findings

Histologic findings are similar to those of any bacterial pyogenic infection. Local destruction of the disk and endplates occurs with infiltration of neutrophils in the early stages. Later, a lymphocytic infiltrate predominates.

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