Objective Positron emission tomography/computed tomography (PET/CT) has not been well studied as a first‐line test for giant cell arteritis (GCA), due, in part, to historical limitations in visualizing the cranial arteries. The Giant Cell Arteritis and PET Scan (GAPS) study was therefore carried out to assess the accuracy of a newer generation PET/CT of the head, neck, and chest for determining a diagnosis of GCA. Methods In the GAPS study cohort, 64 patients with newly suspected GCA underwent time‐of‐flight PET/CT (1‐mm slice thickness from the vertex to diaphragm) within 72 hours of starting glucocorticoids and before undergoing temporal artery biopsy (TAB). Two physicians with experience in PET reviewed the patients’ scans in a blinded manner and reported the scans as globally positive or negative for GCA. Tracer uptake was graded across 18 artery segments. The clinical diagnosis was confirmed at 6 months’ follow‐up. Results In total, 58 of 64 patients underwent TAB, and 12 (21%) of the biopsies were considered positive for GCA. Twenty‐one patients had a clinical diagnosis of GCA. Compared to TAB, the sensitivity of PET/CT for a diagnosis of GCA was 92% (95% confidence interval [95% CI] 62–100%) and specificity was 85% (95% CI 71–94%). The negative predictive value (NPV) was 98% (95% CI 87–100%). Compared to clinical diagnosis, PET/CT had a sensitivity of 71% (95% CI 48–89%) and specificity of 91% (95% CI 78–97%). Interobserver reliability was moderate (κ = 0.65). Among the enrolled patients, 20% had a clinically relevant incidental finding, including 7 with an infection and 5 with a malignancy. Furthermore, 5 (42%) of 12 TAB‐positive GCA patients had moderate or marked aortitis. Conclusion The high diagnostic accuracy of this PET/CT protocol would support its use as a first‐line test for GCA. The NPV of 98% indicates the particular utility of this test in ruling out the condition in patients considered to be at lower risk of GCA. PET/CT had benefit over TAB in detecting vasculitis mimics and aortitis.

Objectives There is uncertainty if varicella zoster virus (VZV) triggers GCA. This is based on discordant reports of VZV detection in GCA temporal artery biopsies. We conducted a multimodal evaluation for VZV in the inception Giant Cell Arteritis and PET Scan (GAPS) cohort. Methods Consecutive patients who underwent temporal artery biopsy for suspected GCA were clinically reviewed for active and past VZV infection and followed for 6 months. Serum was tested for VZV IgM and IgG. Temporal artery biopsy (TAB) sections were stained for VZV antigen using the VZV Mouse Cocktail Antibody (Cell Marque, Rocklin, CA, USA). A selection of GCA and control tissues were stained with the VZV gE antibody (Santa Cruz Biotechnology, Dallas, TX, USA), which was used in previous studies. Results A total of 58 patients met inclusion criteria, 12 (21%) had biopsy-positive GCA and 20 had clinically positive GCA. None had herpes zoster at enrolment and only one patient developed a VZV clinical syndrome (zoster ophthalmicus) on follow-up. There was no difference in VZV exposure between GCA and non-GCA patients. None of the 53 patients who had VZV serology collected had positive VZV IgM antibodies. VZV antigen was not convincingly demonstrated in any of the TAB specimens; 57 TABs stained negative and 1 stained equivocally positive. The Santa Cruz Biotechnology VZV antibody exhibited positive staining in a range of negative control tissues, questioning its specificity for VZV antigen. Conclusion The absence of active infection markers argues against VZV reactivation being the trigger for GCA. Non-specific immunohistochemistry staining may account for positive findings in previous studies.

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Aim: Positron emission tomography/computed tomography (PET/CT) can detect cranial and large vessel inflammation in giant cell arteritis (GCA). We aimed to determine the change and significance of vascular activity at diagnosis and 6 months.Method: Newly diagnosed GCA patients underwent time-of-flight fluorine-18-fluoro-2-deoxyglucose PET/CT from vertex to diaphragm within 72 hours of commencing corticosteroids and were followed for 12 months. A 6 months scan was performed in patients with inflammatory features on biopsy or CT aortitis. Vascular uptake was visually graded by 2 blinded readers across 18 artery segments from 0 (no increased uptake) to 3 (very marked uptake). Scores were summed to give a total vascular score (TVS). Results:We enrolled 21 GCA patients and 15 underwent the serial scan. Twelve (57%) patients experienced a relapse and 5 of these had ischemic features of vision disturbance, jaw or limb claudication. The median TVS fell from 14 (interquartile range [IQR] 4-24) at baseline to 5 (IQR 0-10) at 6 months (P < .01) with reduction in both cranial and large artery scores. While the overall relapse rate was similar between patients with a high (≥10) and low baseline TVS, patients with high scores were numerically more likely to experience an ischemic relapse (33% vs 11%, P = .34). Five out of 15 patients had persistent uptake in at least 1 vessel on the serial PET/CT but none experienced a subsequent relapse. Conclusion:Vascular activity decreased in cranial and large arteries between diagnosis and 6 months. Persistent activity did not predict subsequent relapse. K E Y W O R D S giant cell arteritis, positron emission tomography, prognosis, systemic vasculitis | 583 SAMMEL Et AL.

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