Musculoskeletal infection with M tuberculosis accounts for 1–5% of cases of tuberculosis (TB) and can produce spondylitis (Pott disease), arthritis, osteomyelitis, tenosynovitis, bursitis, and pyomyositis. In developing countries, where the prevalence of TB is high, musculoskeletal TB remains an important source of morbidity and mortality, particularly among children. In the developed world, musculoskeletal TB is uncommon and largely affects adults. Immigrants from countries where TB is prevalent account for a substantial proportion of musculoskeletal TB in the United States and Europe. Musculoskeletal infection has been reported in HIV-infected persons and in patients whose TB reactivated in the setting of anti-tumor necrosis factor therapy. Tuberculosis is a reportable disease and suspected or proven cases should be reported to local public health authorities.

Spinal Tuberculosis (Pott Disease)

Essentials of Diagnosis

• Back pain.
  
• Radiographic evidence of spondylitis or spondylodisciitis.
  
• Identification of M tuberculosis in aspirates or biopsy specimens of skeletal lesions.

General Considerations

Tuberculosis of the spine accounts for approximately 50% of musculoskeletal TB. The thoracic and lumbar vertebrae are most often affected; the cervical spine is involved in less than 10% of cases. Organisms reach the vertebrae either by hematogenous spread (at the time of initial infection or during reactivation) or through lymphatic spread from renal, pleural, or other foci of disease. Most patients do not have active TB at sites outside the skeleton. Pulmonary TB, which is the most common form of concomitant extraskeletal disease, occurs in less than 20% cases.

Infection usually begins within the body of a vertebra and then extends to involve adjacent vertebrae and disks; however, “skipping” to noncontiguous vertebrae is not rare. Soft-tissue involvement is common, and paravertebral cold abscesses develop in about 75% of cases. Isolated involvement of the posterior elements is unusual (5% in one large series).

Clinical Findings

Symptoms and Signs

The most common presenting complaint is pain localized to the spine. The pain typically is not relieved by rest and may be present for months or longer before the patient seeks medical attention. In contrast to pulmonary TB, constitutional symptoms (weight loss, fever, and night sweats) occur in only 50% of cases.

Radicular pain is common. Approximately 50% of patients have lower extremity weakness at presentation; these figures are higher in case series from the developing world. Compression of either the cauda equina or the spinal cord by an inflammatory mass or abscess is the leading cause of neurologic compromise. Meningitis and meningomyelitis are less common. Severe spinal instability can lead to compression or ischemia of the cord.

Destruction of the anterior vertebral body can result in severe angular kyphosis: the gibbus deformity of Pott disease. Paravertebral cold abscesses can track from the lumbar vertebrae along the psoas muscle and present as inguinal masses or can extend from the thoracic spine into the pleural space. Fistulae occur in a small number of patients. In a small percentage of cases, bone can become superinfected with pyogenic organisms.

Laboratory Findings

Routine laboratory investigations are of little diagnostic help. Patients may or may not manifest a peripheral leukocytosis. There usually is a moderate elevation in the erythrocyte sedimentation rate (ESR), but in 10% of cases the ESR is <20 mm/hour.

Imaging Studies

Plain radiographs can be normal early in the course of disease but then demonstrate evidence of spondylitis, including osteolysis, a combination of lytic and sclerotic lesions, and bony destruction that classically is confined to the vertebral body. Although initially there may be relative preservation of the intervertebral disk, disk narrowing is common later in the disease course. CT and MRI reveal changes earlier than plain radiography, provide greater detail of the extent of bony involvement, and can reveal paraspinal abscesses not suspected on clinical grounds. MRI permits prompt detection of compression of the spinal cord or cauda equina and is the preferred imaging technique in cases with signs or symptoms of neurologic compromise.

Special Tests

Most patients (75–90%) have a positive reaction to purified protein derivative (PPD). In one recent series from India, the sensitivity of an interferon-gamma release assay for TB was 84%. Cultures of material obtained by percutaneous needle aspiration of paraspinal abscesses, percutaneous needle biopsy of spinal lesions, and open surgical biopsy are positive for M tuberculosis in 70–90% of reported cases. Smears of biopsy material reveal acid-fast bacilli in a lower percentage (20–25%) than do smears of aspirates of paraspinal abscesses (60%). Biopsies reveal characteristic caseating granulomas in 70%. These percentages on the yields of culture, staining, and histopathology may be inflated by the relatively strict case definitions of the studies. The bacillary burden in spinal TB is low, and some writers with extensive clinical experience in endemic areas estimate that the false-negative rates of aspirates and biopsies approach 50%. Nucleic acid amplification tests may facilitate earlier diagnosis but have only been studied in small numbers of patients with spinal TB, and these tests are not approved by the Food and Drug Administration for diagnosis of extrapulmonary tuberculosis. In patients with extraspinal disease suggestive of tuberculosis, identification of M tuberculosis at another site is sufficient to establish the diagnosis of spinal TB.

Differential Diagnosis

Pyogenic or fungal osteomyelitis or neoplasm can cause disease that is clinically indistinguishable from tuberculous spondylitis. Pyogenic vertebral osteomyelitis generally has a more acute presentation and is more often associated with fever and clinical toxicity than spinal TB. Blood cultures are positive for Staphylococcus aureus, streptococci, or enteric Gram-negative organisms in approximately 50% of cases of pyogenic vertebral osteomyelitis; but in up to 25% of cases, routine bone and blood cultures will not yield an organism. Imaging studies cannot reliably differentiate pyogenic and tuberculous spondylitis. Noncaseating granulomas, which occasionally are the only histologic evidence of spinal TB, can be seen on biopsy specimens of vertebral osteomyelitis due to Brucella or fungi (either of which can mimic spinal TB clinically). Certain imaging features, such as the presence of paravertebral abscesses, can help distinguish spinal TB from neoplastic disease, but these are not always present.

Treatment

Antimicrobial therapy is the cornerstone of treatment for spinal TB. Unless there is strong suspicion of resistance to first-line drugs, most authorities recommend a 6- to 9-month course of therapy with isoniazid, rifampin, pyrazinamide, and ethambutol for 2 months followed by isoniazid and rifampin for 4–7 months.