Comparative analysis of arterial involvement in predominant cranial and isolated extracranial phenotypes of giant cell arteritis using 18F-FDG PET-CT

Objective: To investigate differences in arterial involvement patterns on F-18-FDG PET-CT between predominant cranial and isolated extracranial phenotypes of giant cell arteritis (GCA). Methods: A retrospective review of F-18-FDG PET-CT findings was conducted on 140 patients with confirmed GCA. The patients were divided into two groups: the cranial group, which presented craniofacial ischemic symptoms either at diagnosis or during follow-up, and the isolated extracranial group which never exhibited such manifestations. Results: Of the 140 patients (90 women), 99 (71%) were considered to have a predominantly cranial phenotype, while 41 (29%) had isolated extracranial GCA. Patients with the extracranial phenotype were younger (p = 0.001), had lower TAB positivity (25%), and experienced longer diagnostic delays (p = 0.004). Polymyalgia rheumatica was more common in the extracranial group (p = 0.029), which also showed fewer constitutional symptoms, milder increases in acute phase reactants, and more frequent limb claudication and aortic complications, although these differences were not statistically significant. When comparing arterial involvement on F-18-FDG PET-CT, we observed statistically significant differences. The extracranial phenotype showed greater involvement across all segments of the thoracic aorta (p = 0.001), as well as in the abdominal aorta (p = 0.005), subclavian (p = 0.021), iliac (p = 0.004), and femoral arteries (p = 0.025). In contrast, the cranial phenotype exhibited a higher frequency of vertebral artery involvement (p < 0.001). Conclusion: Significant differences in arterial involvement patterns on F-18-FDG PET-CT were observed between phenotypes. These findings may explain atypical symptoms such as inflammatory lower back pain or limb claudication and the increased risk of aortic complications in extracranial GCA.