Background/Purpose: Performing whole body imaging inevitably reveals incidental findings in the majority of cases. A clinical trial was conducted to determine whether different treatment strategies for RA impact cardiovascular risk through measurement of arterial inflammation via ¹⁸F-FDG PET/CT. Participants recruited to this trial underwent a whole body FDG-PET/CT at the beginning of the trial and at 24 weeks after a step-up in RA treatment. To our knowledge, there is limited data on large populations of people with RA who have had whole body FDG-PET/CT scans performed for non-oncologic reasons. The prevalence of incidental findings in this population is therefore unclear.

Methods: Whole body FDG-PET/CT scans were performed for the 159 participants enrolled in the clinical trial and were interpreted by a radiologist to identify incidental findings. The radiology reports were reviewed and incidental findings were categorized by body system and FDG-avidity. An incidental finding was defined as any finding on the CT or PET component of the scan which was not related to the study objective. A clinically actionable finding was defined as any finding the reading radiologist flagged for further follow-up excluding recommendations to correlate clinically. A finding present on both the baseline and follow-up scan was only counted once. For FDG-avid lymph nodes, the maximum standardized uptake value (SUV) was reported if available and the change in SUV was calculated if applicable.

Results: There were one or more incidental findings in 82% of participants. There was one or more FDG-avid incidental finding in 62% of participants. There were 46 clinically actionable findings noted for a total of 40 participants. Further imaging was recommended for 28 findings. Specialist consultation or procedural evaluation was recommended for 15 findings. The most common non-FDG avid findings were pulmonary nodules, diverticulosis, cholelithiasis, sinus disease, and vascular calcifications. The most common FDG-avid findings were hypermetabolic lymphadenopathy (LAD), increased gastric/esophageal uptake, increased bowel uptake, and increased pharyngeal uptake. LAD was noted in at least one region in 39% of participants. FDG-avid LAD was present in 35% of participants. The median maximum SUV was 5.1 (IQR 3.8-6.8). The most common site of LAD was the axillary region with 26% of participants having enlarged or hypermetabolic axillary lymph nodes.

Conclusion: The majority of incidental findings were interpreted by radiologists to be benign or to not require further evaluation. The most common incidental finding was hypermetabolic axillary LAD. It is not known how the degree of incidentally noted LAD in this study compares to that in the general population.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/incidental-findings-on-whole-body-18f-fdg-pet-ct-in-a-rheumatoid-arthritis-clinical-trial-population/