Abstract
Purpose: White blood cell (WBC) scintigraphy is considered the gold-standard nuclear imaging technique for diagnosing fracture-related infection (FRI). Correct interpretation of WBC scans in FRI is important since a false positive or false negative diagnosis has major consequences for the patient in terms of clinical decision-making. The European Association of Nuclear Medicine (EANM) guideline for correct analysis and interpretation of WBC scans recommends semiquantitative analysis of visually equivocal scans. Therefore, this study aims to assess the diagnostic accuracy of semiquantitative analysis of visually equivocal WBC scans for diagnosing FRI. Methods: A retrospective single-center study was performed in consecutive patients who received WBC scintigraphy in the diagnostic work-up for FRI between February 2012 and January 2017. All the visually equivocal scans were analysed using semiquantitative analysis by comparing leukocyte uptake in the manually selected suspected infection focus with the contralateral bone marrow (L/R ratio). Cut-off points for a ‘positive’ scan result of >0%, >10% and >20% leukocyte increase between the early and late scans were used in separate analyses. The discriminative ability was quantified by calculating the sensitivity, specificity and diagnostic accuracy. Results: In total, 153 WBC scans were eligible for inclusion. After visual assessment of all the scans, 28 visually equivocal scans were included. Dichotomization of the ratios using the cut-off of >0% resulted in a sensitivity of 30%, a specificity of 45% and a diagnostic accuracy of 40%. The >10% cut-off point resulted in a sensitivity of 18%, a specificity of 82% and a diagnostic accuracy of 66%. The >20% cut-off point resulted in a sensitivity of 0%, a specificity of 89% and a diagnostic accuracy of 67%. Conclusion: Semiquantitative analysis of visually equivocal WBC scans is insufficient for correctly diagnosing FRI.
Highlights
Diagnosing fracture-related infection (FRI) can be challenging, and several diagnostic imaging modalities have been proposed [1,2,3,4,5,6,7]
White blood cell (WBC) scintigraphy has been proven to be accurate in diagnosing infections of both bone and soft tissue
A recent retrospective study from our study group analyzed the accuracy of WBC scintigraphy in 192 patients with suspected FRI using the current acquisition and interpretation guidelines and found a diagnostic accuracy of 92% using qualitative assessment [6]
Summary
Diagnosing fracture-related infection (FRI) can be challenging, and several diagnostic imaging modalities have been proposed [1,2,3,4,5,6,7]. In 2013, a dual timepoint acquisition protocol was proposed with imaging 3–4 and 20–24 h after injection of autologous technetium-labeled white blood cells. This protocol has become the standard and is recommended in the latest European Association of Nuclear Medicine (EANM) guideline on WBC scintigraphy [8]. In case of equivocal visual findings, semiquantitative analysis of leucocyte uptake between the early and late scans is recommend in the guideline This semiquantitative method comparing the uptake in a manually selected suspected infection focus with the contralateral bone marrow showed high diagnostic accuracy in a small number of patients with FRI [7]. Similar results were reported in a group of suspected prosthetic joint infections [9]
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