Semi-quantitative analysis with 99mTc-Besilesomab in musculoskeletal system infections.

Objectives: To evaluate the usefulness of 99mTc-Besilesomab to diagnose infectious processes by using monoclonal antibodies BW 250/183 in a semi-quantitative analysis, and to determine the effect on diagnostic capacity of different thresholds for the difference between counts in early versus delayed images. Methods: The study included 77 patients with suspected osteomyelitis who underwent scintigraphy with 99mTc-Besilesomab. After confirming the absence of human anti-mouse antibodies in all patients, early and delayed static images were acquired at 4 and 24 h post-injection, respectively. Visual and semi-quantitative analyses were conducted of regions of interest (ROIs) in areas suspected of infection on early and delayed images. Findings were considered positive when the ratio between counts in delayed and early images exceeded a given threshold after correction for decay. The definitive diagnosis was obtained by clinical follow-up, microbiological culture, or response to medical and/or surgical treatment. Results: The optimal threshold was 1.02 (i.e., positive result = count increase of >2 % in delayed image), obtaining a sensitivity of 0.864, specificity of 0.858, positive predictive value of 0.708, negative predictive value of 0.940, and accuracy of 0.860. Application of the usual threshold of 1.10 (10 %) reduced the sensitivity to 0.734. Conclusion: Semi-quantitative analysis of studies with 99mTc-Besilesomab is a useful technique for the diagnosis of musculoskeletal system infections and contributes to the definitive diagnosis when visual assessments are doubtful or non-conclusive.