Pott Disease (Tuberculous [TB] Spondylitis) Workup

Updated: Aug 08, 2019
  • Author: Jose A Hidalgo, MD; Chief Editor: John L Brusch, MD, FACP  more...
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Workup

Approach Considerations

Laboratory studies used in the diagnosis of Pott disease include the following:

  • Tuberculin skin test (PPD) - Results are positive in 84-95% of patients with Pott disease who are not infected with HIV
  • Erythrocyte sedimentation rate (ESR) - May be markedly elevated (>100 mm/h)
  • Microbiologic and PCR studies - Used to confirm the diagnosis

With regard to the above-mentioned microbiologic studies, bone tissue or abscess samples are obtained to stain for acid-fast bacilli (AFB), culture and susceptibility, and DNA amplification. Procedures guided by computed tomography (CT) scanning can be used to guide percutaneous sampling of affected bone or soft-tissue structures. These study findings are positive in only about 50% of the cases. A 2015 multicentric, multinational study involving 35 centers and 314 cases reported that the causative agent was identified in 41% of cases. [28] Surgical biopsies can also be considered for tissue sampling.

Nonculture methods (DNA amplification) using skeletal tissue samples offer a high diagnostic yield and high specificity (96%), high sensitivity (95%), and rapid results (2 days). [29, 30, 31] An additional potential advantage is simultaneously identifying drug resistance and improving outcomes. [32]

Biopsy

Percutaneous, CT scan ̶ guided needle biopsy of bone lesions is a safe procedure that also allows therapeutic drainage of large paraspinal abscesses. Obtain a tissue sample for microbiologic and pathologic studies to confirm diagnosis and to isolate organisms for culture and susceptibility. Positive culture yield of percutaneous is 50-83% and appears to be influenced by technical details, such as decontamination of specimens prior to culture. [33]

Histologic findings

Because microbiologic studies may be nondiagnostic of Pott disease, anatomic pathology can be significant. Gross pathologic findings include exudative granulation tissue with interspersed abscesses. Coalescence of abscesses results in areas of caseating necrosis.

Drainage

Some cases of Pott disease are diagnosed following an open drainage procedure (eg, following presentation with acute neurologic deterioration).

Scintigraphy

Radionuclide scanning findings are not specific for Pott disease. Gallium and technetium bone scans yield high false-negative rates (70% and up to 35%, respectively). [34]

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Radiography

Radiographic changes associated with Pott disease present relatively late. The following are radiographic changes characteristic of spinal tuberculosis on plain radiography: [35]

  • Lytic destruction of anterior portion of vertebral body

  • Increased anterior wedging

  • Collapse of vertebral body

  • Reactive sclerosis on a progressive lytic process

  • Enlarged psoas shadow with or without calcification

Additional radiographic findings may include the following:

  • Vertebral end plates are osteoporotic.

  • Intervertebral disks may be shrunk or destroyed.

  • Vertebral bodies show variable degrees of destruction.

  • Fusiform paravertebral shadows suggest abscess formation.

  • Bone lesions may occur at more than 1 level.

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CT Scanning

CT scanning provides much better bony detail of irregular lytic lesions, sclerosis, disk collapse, and disruption of bone circumference. [36]

Low-contrast resolution provides a better assessment of soft tissue, particularly in epidural and paraspinal areas.

CT scanning reveals early lesions and is more effective for defining the shape and calcification of soft-tissue abscesses. In contrast to pyogenic disease, calcification is common in tuberculous lesions.

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MRI

Magnetic resonance imaging (MRI) is the criterion standard for evaluating disk-space infection and osteomyelitis of the spine and is most effective for demonstrating the extension of disease into soft tissues and the spread of tuberculous debris under the anterior and posterior longitudinal ligaments. [37] MRI is also the most effective imaging study for demonstrating neural compression. [38, 39]

Contrast-enhanced MRI findings are useful in differentiating tuberculous spondylitis from pyogenic spondylitis. MRI findings in Pott disease include thin and smooth enhancement of the abscess wall and a well-defined paraspinal abnormal signal. Thick and irregular enhancement of the abscess wall and an ill-defined paraspinal abnormal signal suggest pyogenic spondylitis. [40] The images below are studies of a man aged 31 years with spinal tuberculosis.

Involvement of the disk is typically a characteristic of infectious spondylitis; however, this may not always be the case, and Pott disease can present with atypical features resembling neoplastic lesions. Findings of an intradural extramedullary mass at the lower end of the spinal cord associated with holocord T2 hyperintensities of the choroid has been described in intramedullary tubercular abscesses ”precipitation sign." [41, 42, 43, 44]

Three MRI parameters have been found to be strongly suggestive of spinal tuberculosis: subligamentous spread of abscess, vertebral body collapse, and large abscess collection with thin abscess wall. A combination of these MRI findings has a higher predictive value, an odds ratio of 16.3 when comparing a group of patients with spinal tuberculosis versus a group of patients evaluated for spondylodiscitis with a different diagnosis. [45]

MRI of a 31-year-old man with tuberculosis of the MRI of a 31-year-old man with tuberculosis of the spine. Images show the thoracic spine before and after an infusion of intravenous gadolinium contrast. The abscess and subsequent destruction of the T11-T12 disc interspace is marked with arrowheads. Vertebral body alignment is normal. Courtesy of Mark C. Diamond, MD, and J. Antonio Bouffard, MD, Detroit, Mich.
MRI of the T11 in a 31-year-old man with tuberculo MRI of the T11 in a 31-year-old man with tuberculosis of the spine. Extensive bone destruction consistent with tuberculous osteomyelitis is evident. The spinal cord has normal caliber and signal. No evidence of spinal cord compression or significant spinal stenosis is distinguishable. Courtesy of Mark C. Diamond, MD, and J. Antonio Bouffard, MD, Detroit, Mich.
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