• Giant Cell Arteritis
• Disease Activity
• Inflammation

In a prospective case–control study recently published in the Annals of Rheumatic Diseases, Prieto-González et al1 have shown a high sensitivity and specificity of positron emission tomography (PET)/CT with ¹⁸fluorodeoxyglucose (FDG) in 32 patients with newly diagnosed, biopsy-proven giant cell arteritis (GCA). Using receiver–operator characteristic curves (ROC) analysis, the authors determined cut-off maximal standardised uptake values (SUVm) to detect vascular inflammation by PET/CT. The sensitivity and specificity of PET/CT obtained in this study was close to that calculated in a recent meta-analysis of mostly retrospective studies.2

We used PET with FDG for diagnosis and assessment of activity of vascular inflammation in 12 patients with GCA (3 males and 9 females, age 72–75 years). FDG uptake was found in 11 of 12 patients. In the majority of patients, PET showed involvement of different large arteries, including common carotid arteries (in 9), ascending (in 2), thoracic (in 7) and abdominal (in 7) aorta, brachiocephalic (in 5), subclavian (in 5) and axillar (in 2) arteries, aortic arch (1) and pulmonary arteries (in 1). High FDG uptake was present in all five untreated patients, while it was absent or borderline in four of seven patients who were receiving corticosteroids. Nevertheless, significant FDG uptake detected by PET in three treated patients confirmed persistent activity of vascular inflammation and justified intensification of immunosuppressive treatment. PET was especially valuable for the diagnosis of GCA with predominant large vessels involvement in seven patients. As in the Prieto-González et al study, in our series the results of PET usually correlated with laboratory markers of activity (erythrocyte sedimentation rate, C-reactive protein, interleukin-6).

We agree with Prieto-González et al that positive PET/CT may be (or probably better to say should be) accepted in the near future as an independent diagnostic criterion. It is already used as such in the ongoing pivotal tocilizumab trial in patients with GCA.3 In our opinion, PET/CT is an especially valuable diagnostic tool in patients with large vessel involvement who do not have typical GCA manifestation. In combination with other non-invasive methods, it can replace temporal artery biopsy in the centres where the latter is not available or if the patient has contraindications or declines invasive intervention. The diagnostic accuracy of PET in detecting vascular inflammation is higher in patients not receiving immunosuppressive therapy.2 But in our series, PET was also useful in few patients with persistent activity in spite of corticosteroid treatment. Should we use PET/CT to assess activity of GCA? In the Prieto-González et al study and in our series, FDG uptake correlated with standard laboratory markers of inflammation. Therefore, at least to date we cannot recommend routine use of this expensive method for the assessment of GCA activity though it can be probably used in the selected patients. Further studies are needed to answer this question and to evaluate the diagnostic performance of PET/CT in patients with suspected GCA.