ESSENTIALS OF DIAGNOSIS
Seen primarily in immigrants from developing countries or immunocompromised patients.
Back pain and gibbus deformity.
Radiographic evidence of vertebral involvement.
Evidence of Mycobacterium tuberculosis in aspirate or biopsies of spinal lesions.
In the developing world, children primarily bear the burden of musculoskeletal tuberculosis. In the United States, however, musculoskeletal infection is more often seen in adult immigrants from countries where tuberculosis is prevalent, or it develops in the setting of immunosuppression (eg, HIV infection, therapy with TNF inhibitors). Spinal tuberculosis (Pott disease) accounts for about 50% of musculoskeletal infection due to M tuberculosis (see Chapter 9-13). Seeding of the vertebrae may occur through hematogenous spread from the respiratory tract at the time of primary infection, with clinical disease developing years later as a consequence of reactivation, or through lymphatics from infected foci in the pleura or kidneys. The thoracic and lumbar vertebrae are the most common sites of spinal involvement; vertebral infection is associated with paravertebral cold abscesses in 75% of cases.
Patients complain of back pain, often present for months and sometimes associated with radicular pain and lower extremity weakness. Constitutional symptoms are usually absent, and less than 20% have active pulmonary disease. Destruction of the anterior aspect of the vertebral body can produce the characteristic gibbus deformity.
Most patients have a positive reaction to purified protein derivative (PPD) or a positive interferon-gamma release assay. Cultures of paravertebral abscesses and biopsies of vertebral lesions are positive in up to 70–90%. Biopsies reveal characteristic caseating granulomas in most cases. Isolation of M tuberculosis from an extraspinal site is sufficient to establish the diagnosis in the proper clinical setting.
Radiographs can reveal lytic and sclerotic lesions and bony destruction of vertebrae but are normal early in the disease course. CT scanning can demonstrate paraspinal soft tissue extensions of the infection; MRI is the imaging technique of choice to detect compression of the spinal cord or cauda equina.
Spinal tuberculosis must be differentiated from subacute and chronic spinal infections due to pyogenic organisms, Brucella, and fungi as well as from malignancy.
Paraplegia due to compression of the spinal cord or cauda equina is the most serious complication of spinal tuberculosis.
Antimicrobial therapy should be administered for 6–9 months, usually in the form of isoniazid, rifampin, pyrazinamide, and ethambutol for 2 months followed by isoniazid and rifampin for an additional 4–7 months (see also Chapter 9-13). Medical management alone is often sufficient. Surgical intervention, however, may be indicated when there is neurologic compromise or severe spinal instability.