Effect of Causative Micro-organisms on Patterns of Labeled White Blood Cells in Osteomyelitis

OBJECTIVE: The aim of this study is to investigate the effect of microbiological characteristics of causative organisms on the scintigraphic patterns of labeled-white blood cells (WBC) scan in cases of proven osteomyelitis. MATERIALS AND METHODS: Retrospective analysis of 25 patients referred with suspected osteomyelitis and had both bone and labeled-WBC scans performed and complete records of the microbiological culture of the causative organism. The bone and labeled-WBC scans were retrieved and reviewed by two nuclear medicine physicians. Any definite focal accumulation of labeled WBCs within the bone was considered positive for osteomyelitis. Diagnosis of osteomyelitis in the discharge summary was considered the reference standard and was based on a combination of the clinical scenario, imaging, and laboratory findings including microbiology. Correlation of the pattern of labeled WBC and the type of microorganisms was done. RESULTS: A total of 16 patients were included in this study, seven females and nine males. Of these, seven patients had Gram-positive whereas nine patients had Gram-negative organisms. The majority (85.7%) of Gram-positive organisms showed increased accumulation of labeled WBCs, whereas only one-third (33.3%) of patients with Gram-negative organisms had such finding. CONCLUSION: The pattern observed in this study shows that the false-negative results of labeled-WBC scans were mainly noted in patients with Gram-negative as opposed to Gram-positive infections. This confirms the experimental animal study findings that the secretion of anti-chemotactic factors by Gram-negative organisms, seems to be inhibiting the migration of labeled WBCs to the site of infection. The inhabitation is decreasing the accumulation of labeled WBCs and consequently resulting in a false-negative finding. The study adds to evidence that microbiological characteristics of the causative organisms are another explanation for the false-negative WBC in proven osteomyelitis.