Several months later, the patient complained of severe back pain in the mid-dorsal spine. Physical examination was unremarkable except for point tenderness in the mid-dorsal spine. The only exposure to tuberculosis was to his father who had active disease in his youth. Lab results showed normal WBC, low RBC, low hematocrit, and persistently elevated ESR of 105 mm/hr., which never went below 100 mm/hr.
Two months later the patient complained of vague low back pain. Plain films showed left SI joint destruction. CT (arrow) and Gallium-67 citrate scintigraphy (arrow) showed left psoas abscess with SI joint destruction. Results of a CT guided aspiration of the psoas abscess were positive for tuberculous bacillus.
Skeletal tuberculosis constitutes 35% of extrapulmonary disease with the spine affected 50-60% of the time (2). The thoracolumbar spine is most often affected (2) with less frequent involvement of the cervical and sacral spine. Unilateral SI joint involvement is not uncommon (2,3). Pott's disease presents in the mid-thoracic spine and thoracolumbar junction.
The primary focus for infection is different for different age groups. In a series of 499 patients, 31% showed a radiographically demonstrated source in the lung. Of these 78% were children. The remaining 69% showed a normal chest X-ray and were mostly adults. In the adult, silent foci such as kidney, gut, and tonsil were the primary source.
Owing to the distribution of the vertebral arterial supply, involvement of adjacent vertebrae are possible. When large vertebral segments or multiple segments with intervening normal zones are present, the paravertebral venous plexus of Batson is implicated. Bony changes are seen two to five months after infection. Usually, the subchondral regions of the vertebral body are affected. When the anterior and lateral portions of the vertebral body are affected, vertebral collapse occurs resulting in kyphosis and gibbus deformity. Involvement of the posterior vertebral body results in cavitation and an extradural mass. Kyphosis occurs in the thoracic spine while the lumbar spine telescopes on itself as it collapses. The disc space is eventually destroyed, but at a slower rate than pyogenic infection.
Tuberculosis can spread from a spinal focus by direct extension through the disc space. Once a paravertebral abscess is formed, the disease can spread via anterior/posterior longitudinal ligaments and extend to the pleural space. From the cervical vertebrae the disease can travel to the posterior triangle of the neck or retropharnyx. The abscess can also track along fascial planes to create a psoas abscess or can extend posteriorly to form an extradural abscess.
Clinically patients present with pain over the affected vertebra, low grade fever, chills, weight loss. ESR may be elevated. Duration of symptoms range from 2 weeks - 3 years with a mean of one year. Positive skin tests range from 77% to 100% (2). Significant number of smears and cultures of spinal biopsies may be negative (2). In the advanced stage, cold abscesses, spinal deformity, and sinus tracts develop. Neurological deficits also occur and affect 13% of patients. Years after resolution of the initial infection, stretching of spinal cord over bony deformity can lead to paraplegia. Calcification may occur in long-standing abscesses.
Plain films and tomography are useful for assessing vertebral destruction, but they may be normal. CT demonstrates the extent of bony and soft tissue involvement. Technetium-99m MDP bone scintigraphy, though invaluable, can remain positive for a very long time which limits the value of this modality for following response to therapy. When a bone scan is positive, specificity can be improved by doing pinhole views which can differentiate tuberculosis from pyogenic spondylitis or from metastasis (4). Normal Tc-99m bone scans have been reported where there were radiographically and surgically proven sites of active disease. This finding may be due to either the indolent nature of the infection or overwhelming infection inciting little bone response. Ga-67 citrate scintigraphy is useful to define total extent of infection and follow response to therapy since the scans resolve within months of initial therapy. A few cases in the literature have shown normal Ga-67 citrate scans (2,3). No explanation could be found for this. In the instances of negative scans, In-111 white cell imaging may be useful, but this experience is limited.
Tuberculous spondylitis is a complex disease with varied manifestations. Radionuclide imaging is valuable in detection and follow-up of this disease. When radionuclide imaging is normal, one should obtain tissue specimen to confirm or exclude presence of disease.
2) Gorse GJ, Pais JM, et al. Tuberculous spondylitis: a report of six cases and review of the literature. Medicine 1983; 62(3):178-193.
3) Lifeso RM, et al. Tuberculous spondylitis in adults. The Journal of Bone and Joint Surgery. 1985; 65A(9):1405-1413.
4) Bahk YW, et al. Pinhole collimator scintigraphy in differential diagnosis of metastasis, fracture, and infections of the spine. J Nucl Med 1987; 28:447-451.
J. Anthony Parker, MD PhD, email@example.com