Review Question - QID 2209

Decreasing C-reactive protein (CRP) levels are the most reliable method of tracking response to antibiotic treatment in vertebral osteomyelitis.

Vertebral osteomyelitis occurs most commonly in the lumbar spine in adults in their 50's or 60's. Patients often present afebrile with negative blood cultures and a normal WBC count. Imaging helps narrow the diagnosis and biopsy can be performed to confirm the organism. If no organism is isolated and the patient is neurologically intact without gross instability, treatment with empiric antibiotics is indicated. Response to treatment is judged based on improvement in laboratory studies, specifically CRP given its short half-life of 19 hours.

Mok et. al prospectively followed pre-operative and postoperative CRP and ESR levels in 149 patients undergoing spinal surgery. They found no postoperative trend could be determined for ESR, however, CRP demonstrated a predictable rise and fall with deviations from expected kinetics correlating with infection. They conclude knowledge of normal CRP kinetics postoperatively may assist in the identification of infection.

Cornett et al. reviewed bacterial spine infections with regard to pathophysiology, diagnosis, and treatment. They state that CRP levels are nonspecific but are more useful than ESR in monitoring therapy given shorter normalization time. They found that CRP and ESR are 98% and 100% sensitive, respectively.

Figure A shows T1 sagittal MRI showing L5-S1 with decreased marrow signal of adjacent vertebral endplates and disc space. Figure B shows increased signal in the inferior L5 endplate, superior S1 endplate, and disc space. Figure C shows a post-contrast image with similar L5-S1 post-contrast enhancements.

Incorrect Answers:
Answer 1: Procalcitonin is thought to be slightly less sensitive than CRP for acute osteomyelitis and is under further investigation in musculoskeletal infections.
Answer 2: WBC count is often normal on presentation (45%) and is not as reliable as CRP.
Answer 3: Blood cultures are often negative at presentation and not a reliable method of response to treatment.
Answer 4: ESR takes longer (3 weeks) to normalize and is therefore not as useful for monitoring treatment response.