Pott disease (also known as tuberculous spondylitis) refers to vertebral body and intervertebral disc involvement with tuberculosis.
One of the commoner infections of spine is tuberculosis. Unfortunately, the incidence of tuberculous spondylitis, as with other forms of TB, is on the rise, due to new multiple drug resistant strains.
There is usually a slow collapse of one or usually more vertebral bodies, which spreads underneath the longitudinal ligaments. This results in an acute kyphotic or "gibbus" deformity. This angulation, coupled with epidural granulation tissue and bony fragments, can lead to cord compression. Unlike pyogenic infections, the discs can be preserved. In late-stage spinal TB, large paraspinal abscesses without severe pain or frank pus are common, leading to the expression "cold abscess".
The spread of infection is typically described as 'sub-ligamentous' : beneath the anterior longitudinal ligament, usually sparing the posterior elements and often involving multiple levels.
Tuberculous spondylitis can be difficult to detect in early stages because of relative preservation of the disc space.
A reduction in vertebral height is often seen with irregularity of the antero-superior end plate being relatively early and subtle sign. Due to the subligamenotous extension there may be some irregularity of the anterior vertebral margin. This is a classical appearance with TB spondylitis.
Later, collections can develop with can be remarkably large.
Ivory vertebrae can result with re-ossification. Other associated features may include
As with other extrapulmonary TB, the chest film may be unrevealing (no pulmonary lesions seen in up to 50% of cases), with the source being a primary lung lesion that is clinically silent.
CT and MRI
Cross-sectional imaging is required to better assess the extent of involvement and particularly for the presence of an epidural component and cord compression. MRI is the modality of choice for this, with CT with contrast being a distant second.
Features include irregularity of both the endplate and anterior aspect of the vertebral bodies, with bone marrow oedema and enhancement seen on MRI.
The collections are typically well circumscribed, with fluid centers and well defined enhancing margins.
In many parts of the developing world, TB is the most common cause of vertebral body infection, with the majority of cases seen in patients under the age of 20. TB can also affect the meninges of the spine, causing an intense pachymeningitis that enhances dramatically.
- brucellosis - can present as granulomatous osteomyelitis of the spine that can be difficult to distinguish from TB. Both are acid-fast bacilli, which may cause caseating granuloma(s).
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