Session Type: ACR Late-breaking Abstract Session
Session Time: 4:00PM-6:00PM
Background/Purpose: The diagnostic accuracy of PET/CT against temporal artery biopsy (TAB) in patients suspected of having GCA has not been well studied. PET/CT has traditionally been used to image the aorta and primary branches, but newer generation scanners can also detect inflammation in the smaller temporal (TA), occipital (OA), maxillary (MA) and vertebral arteries (VA). We assessed the accuracy of a newer generation PET/CT time-of-flight scanner for GCA.
Methods: 64 newly suspected GCA patients were enrolled over 20 months. All underwent PET/CT from the vertex to diaphragm within 72 hours of starting corticosteroids and before TAB. Two PET experienced nuclear medicine physicians blinded to clinical and biopsy data independently reported scans as globally positive or negative for GCA. They also rated the grade that tracer (FDG) uptake exceeded background blood pool for 18 artery segments and the maximum grade per patient (0 = none, 1 = minimal/equivocal, 2 = moderate, 3 = very marked). Discordant results were resolved by consensus. The clinical diagnosis was made at the six-month mark by consensus between the PET/CT blinded treating clinician and blinded external reviewers.
Results: 58/64 (91%) patients underwent TAB and 12/58 (21%) biopsies were positive for GCA. 21/64 (33%) had a clinical diagnosis of GCA and 42 (66%) met the 1990 ACR criteria for GCA. Compared with TAB, global GCA assessment by PET/CT had sensitivity (Sn) 92%, specificity (Sp) 85%, positive predictive value (PPV) 61% and negative predictive value (NPV) 98%. Interobserver reliability was good (k = 0.65). Compared with clinical diagnosis, PET/CT had Sn 71% and Sp 91%. 2/7 PET/CT ‘false positive’ cases had GCA consistent disease flares when corticosteroids were weaned. Defining an uptake grade cut-off 1+ in any vessel as a positive scan gave Sn 100% and Sp 46% against TAB while a cut-off 2+ gave Sn 83% and Sp 83%. Four (33%) TAB positive patients had grade 2+ uptake localized to the TA, OA, MA or VA arteries and may have been missed on older generation scans.
Conclusion: This PET/CT protocol had good diagnostic accuracy. The high NPV of 98% indicates that it could be used as a first-line test to rule out GCA.
To cite this abstract in AMA style:Sammel A, Hsiao E, Schembri G, Nguyen K, Brewer J, Schrieber L, Janssen B, Youssef P, Fraser C, Bailey E, Bailey D, Roach P, Laurent R. The Diagnostic Accuracy of PET/CT Scan of the Head, Neck and Thorax Compared with Temporal Artery Biopsy in Patients Newly Suspected of Having GCA [abstract]. Arthritis Rheumatol. 2018; 70 (suppl 10). https://acrabstracts.org/abstract/the-diagnostic-accuracy-of-pet-ct-scan-of-the-head-neck-and-thorax-compared-with-temporal-artery-biopsy-in-patients-newly-suspected-of-having-gca/. Accessed August 6, 2020.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-diagnostic-accuracy-of-pet-ct-scan-of-the-head-neck-and-thorax-compared-with-temporal-artery-biopsy-in-patients-newly-suspected-of-having-gca/