Vertebral osteomyelitis can be complicated by direct seeding in different compartments, resulting in paravertebral, epidural, or psoas abscesses. In one series, vertebral osteomyelitis was complicated by epidural abscess in 17% of cases, paravertebral abscess in 26%, and a disk-space abscess in 5%. One fourth of patients developed motor weakness or paralysis, with particularly high rates among patients with cervical spine osteomyelitis. Neurologic complications have been reported in 38% of patients with vertebral osteomyelitis. In an analysis of 14 case series, vertebral osteomyelitis was complicated by relapse in 8% of cases, and death in 6%.
What organisms are most frequently implicated in pyogenic vertebral osteomyelitis?
Staphylococcus aureus is the most common microorganism implicated in pyogenic vertebral osteomyelitis, followed by E. coli. Coagulase-negative staphylococci and Propionibacterium acnes cause almost exclusively exogenous osteomyelitis after spine surgery, particularly if fixation devices are used. However, in case of prolonged bacteremia (e.g., pacemaker-electrode associated infection), hematogenous vertebral osteomyelitis due to low-virulence microorganisms (e,g., coagulase-negative staphylococci) has been described.
What tests are highly sensitive for the diagnosis of vertebral osteomyelitis?
Increased CRP is highly sensitive for the diagnosis of osteomyelitis, reported in 100% of cases. CRP is the preferred marker of infection, at least in postoperative spinal wound infection. Increased blood leukocyte counts or a high percentage of neutrophils (above 80%) are insensitive for the diagnosis of osteomyelitis. In a systematic review of studies of vertebral osteomyelitis, positive blood cultures were reported in 58% (range across studies, 30 to 78%).
What diagnostic step is recommended if vertebral osteomyelitis is suspected by imaging procedures and blood cultures show no growth?
If vertebral osteomyelitis is suspected by imaging procedures and blood cultures do not show growth, biopsy is generally warranted. Biopsy should be performed regardless of whether or not blood cultures are negative if polymicrobial osteomyelitis is suspected (e.g., intraabdominal sepsis). If the patient has a paravertebral, epidural, or psoas abscess, CT-guided drainage (with stain and culture of the specimen) may make bone biopsy unnecessary. Culture of a biopsy specimen, either CT-guided or open, has a higher overall yield than blood cultures (77%, range across studies 47 to 100%). Bone samples should be cultured for aerobic and anaerobic bacteria and for fungi. In patients with a suggestive history (e.g., stay in endemic region, subacute presentation), cultures should also be performed for mycobacteria and brucella species. In addition, analysis by histopathology is useful, because the presence of leukocytes in the specimens distinguishes infection from contamination.