Diagnostic methodology in labelled leukocyte scan for prosthetic / non-prosthetic osteoarticular infection: Visual or semi-quantitative analysis? One- or two-day protocol?

OBJECTIVE: as scarce literature on the topic is available, we aimed to compare diagnostic utility of semi-quantitative versus visual analysis in labelled white blood cell scintigraphy (WBCS) for osteoarticular infection. One-day and two-day protocols were assessed, particularly in orthopaedic devices. MATERIAL AND METHODS: prospective study of 79 consecutive patients with suspected osteoarticular infection. In all patients, WBCS were performed at 30min, 4h, 8h and 24h. Images were analysed by grouping in two protocols: one-day-protocol (experts evaluated 30min, 4h and 8h planar images) and two-day-protocol (experts evaluated 30min, 4h and 24h planar images). Planar images were interpreted qualitative and semiquantitatively and also were compared grouping patients with and without orthopaedic devices. To find which cut-off value of the percentage variation could predict of osteoarticular infection, multiple cut-off values were calculated in both protocols from the Youden index. Three blinded readers analysed the images. RESULTS: Comparing final diagnosis visual analysis of the one-day-protocol provided better results with sensitivity of 95.5%, specificity of 93% and diagnostic accuracy of 93.7% (p<001) than the two-day-protocol with values of 86.4%, 94.7% and 92.4%, respectively (p<001). For semi-quantitative analysis, the one-day-protocol also obtained better results with sensitivity of 72.7%, specificity of 78.9% and accuracy of 77.2% (p<001) than two-day-protocol (no significant results; p=0.14), especially in the group of patients with orthopaedic devices (sensitivity of 100%, specificity of 79.5% and accuracy of 82.7%; p<001). CONCLUSIONS: most accurate approach in the diagnosis of osteoarticular infection corresponded to visual analysis in one-day-protocol that showed greater sensitivity and specificity than semi-quantitative analysis. Semi-quantitative analysis only could be useful when visual analysis is doubtful. In patients with joint prostheses, an increase in percentage variation above 9% obtained maximum sensitivity and negative predictive value.

Utility of 8 h and time decay-corrected acquisition scintigraphy with in-vitro labeled white blood cells for the diagnosis of osteoarticular infection.

INTRODUCTION: Except in the spine, labeled white-blood cell scintigraphy (WBCS) with image acquisition up to 24 h is the nuclear medicine test of choice for diagnosing osteoarticular infection. However, distinguishing between inflammation and infection is a challenge. OBJECTIVES: The first aim of this study was to verify earlier research studies that used 4 and 24 h time decay-corrected acquisition (TDCA) to differentiate infection from inflammation. The second aim was to analyze whether 8 h acquisition (1-day protocol) yielded similar results as 20-24 h acquisition. PATIENTS AND METHODS: This was an observational study of 94 patients (22-86 years, 52 women) with suspected osteoarticular infection referred to nuclear medicine to confirm infection. WBCS and TDCA images were obtained at 30 min, 4 h, and 8 h after injection of the labeled leukocytes, with collection times of 5, 8, and 12 min, respectively. Scintigrams were classified into three protocols: protocol 1: experts read only 30 min and 4 h images; protocol 2: experts read the whole set of images (30 min, 4 h, and 8 h) with different pixel intensities (each image normalized to its own maximum activity); protocol 3: experts read the whole set of images with the same pixel intensity. Sensitivity, specificity, positive and negative predictive values, and accuracy were calculated. In patients with orthopedic implants, the interobserver reproducibility for visual analysis was calculated using the κ index. RESULTS: Infection was confirmed in 26 cases. Sensitivity, specificity, positive predictive value, negative predictive value, accuracy, and κ results were as follows: protocol 1: 92.3, 50.0, 41.4, 94.4, 61.7%, 0.79; protocol 2: 92.3, 94.1, 85.7, 97.0, 93.6%, 0.80; protocol 3: 96.2, 97.1, 92.6, 98.5, 96.8%, 0.77. CONCLUSION: TDCA acquisition of WBCS at 8 h (1-day protocol) enables a faster diagnosis than 24 h acquisition. The use of TDCA with the same pixel intensity in all images enables an accurate diagnostic of osteoarticular infection, with a considerable interobserver agreement for all protocols.