A case-control study to evaluate the diagnostic accuracy of FDG uptake in cranial arteries by FDG PET/CT in the diagnosis of giant cell arteritis.

Although older studies argue that FDG PET/CT cannot demonstrate inflammation in cranial arteries, e.g. temporal and maxillary arteries, the resolution of modern PET systems may have improved, making a case for FDG PET/CT. FDG PET/CT is increasingly used in giant cell arteritis (GCA) diagnosis due to its excellent diagnostic accuracy considering large-vessel involvement. In case of uncommon distribution of vessel involvement or marginally increased large-vessel FDG uptake, FDG PET/CT-specificity may be compromised. Hence, recognising FDG uptake in cranial arteries potentially adds to FDG PET/CTs diagnostic accuracy.

Objectives To evaluate the diagnostic accuracy of conventional FDG PET/CT of the cranial arteries in the diagnosis of GCA.

Methods In a cohort of consecutively included glucocorticoid-naïve patients suspected of new-onset GCA, patients with a clinical GCA diagnosis will be identified. Conventional FDG PET/CT and vascular ultrasound(US) was performed before treatment. Patients were referred for a temporal artery biopsy (TAB).

Controls are age-(+/- 3 years) and sex-matched malignant melanoma (MM) patients who had a follow-up metastatic-disease-free FDG PET/CT ≥6 months after MM resection.

Images will be assessed by 5 nuclear medicine physicians blinded to clinical symptoms and findings. Temporal (TA), maxillary (MA) and vertebral (VA) arteries will be visually assessed. Arterial FDG uptake more than FDG uptake in surrounding tissue is considered positive. Sensitivity, specificity and interreader agreement will be evaluated.

Inclusion Criteria:

Cases:

• 1) age ≥50 years, 2) CRP>15mg/l or ESR>40mm/h, 3) either a) cranial symptoms, b) new-onset extremity claudication or c) weight loss >5 kilograms or fever>38oC for >3 weeks and a clinical diagnosis of giant cell arteritis judged by expert rheumatologist.

Controls:

• age-(+/-3 years) and sex-matched malignant melanoma (MM) patients
• follow-up metastatic-disease-free FDG PET/CT ≥6 months after MM resection

Exclusion Criteria:

• Previous diagnosis of polymyalgia or giant cell arteritis
• immunosuppresive treatment within last month

All patients are sampled from tertiary hospital. Cases are identified in an established cohort of patients suspected og GCA in whom clinical assessment, including imaging procedures were performed before treatment.

Controls are sampled among malignant melanoma patients who had a clinically indicated follow-up FDG PET/CT to evaluate disease freedom/progression.