This process is presented in juxtaposition to epidural abscess, with which it is closely aligned. As with other forms of osteomyelitis, vertebral infection is typically due to hematogenous implantation of bacteria during episodes of bacteremia or, it is associated with the exogenous introduction of bacteria during spinal surgery, particularly if catheters or other devices, including for spinal stabilization, are incorporated. In the case of postsurgical infection, coagulase-negative staphylococci or propionibacterium are almost always implicated, whereas with bacteremia, a number of low-virulence organisms including staphylococcus are found and multiple organisms may be involved. The source of bacteremia may be urinary infection, endocarditis, or intravenous drug abuse but many affected individuals also have diabetes, are immunosuppressed, have cancer, or are receiving dialysis for renal failure. In the group of immunocompromised patients, unusual or endemic organisms such as Brucella may be found. However, in almost half of patients who have not had surgery, no source is identified. Approximately one-fifth of cases have an associated epidural abscess, as discussed above. This is often indicated by an increase in local back pain or extremely severe pain from the onset.
The lumbar spine is the region most affected (in contrast to the frequent thoracic distribution of epidural abscess). The typical presentation is relatively nondescript with back pain, elevated white blood cell count and C-reactive protein level. Fever, however, is inconsistent. Several types of imaging studies may be used to demonstrate the infection, however, MRI more dependably than CT shows edema within the bone marrow and, if there is destruction of the disc adjacent to an effective vertebral body, infection is almost certain. Technetium bone scans were popular for the demonstration of osteomyelitis in general but the findings may be nonspecific. A well-known adage is that neoplasms affecting the vertebral body do not cross the disc space whereas infections do so.
A point of contention has been the need for biopsy of the affected bone when blood cultures are negative and no obvious source of infection in the body can be found. This procedure is generally suggested although extension of the infection from the vertebral body to the paravertebral or epidural spaces may also be performed under CT guidance.
Initiating therapy with oral fluoroquinolones, with or without rifampin, has been suggested as a broad approach while the specific infecting bacteria are identified. Therapy is generally continued for at least 4 to 6 weeks, if not longer but no clear guidance is available on the appropriate duration. Surgical removal of infected bone is generally not undertaken unless the osteomyelitis is the result of implanted hardware during previous spinal surgery. Almost invariably, this hardware must be removed. Surveillance for persistent infection after treatment is probably appropriate but the MRI has not proven useful for this purpose. Inflammatory markers in the blood are apparently more dependable. A thorough review of this subject can be found in the clinical practice article by Zimmerli.