Impact of previous glucocorticoid therapy on diagnostic accuracy of [18F] FDG PET-CT in giant cell arteritis

Objective: To evaluate the impact of prior glucocorticoid (GC) treatment on the diagnostic accuracy of 18F-FDG PET-CT in giant cell arteritis (GCA).Methods: Retrospective study of a consecutive cohort of 85 patients with proven GCA who received high-dose GC before PET-CT.Results: Thirty-nine patients previously treated with methylprednisolone (MP) boluses, of whom 37% were PETCT (uptakes grade 3 or 2) positive. The positivity rate was 80% with MP doses of 125 mg, 33% with 250 or 500 mg, and 0% with doses of 1 g. If we also classify as positive those cases with a grade 1 uptake (with a circumferencial uptake and smooth linear or long segmental pattern, possibly indicative of "apparently inactive" vasculitis), the positivity rate increases to 62% (100%, 50-60%, and 33% for the different MP doses, respectively).In patients with new-onset GCA treated with high-dose oral GC, PET-CT positivity was 54.5% in patients treated for less than two weeks, 38.5% in those treated for 2 to 4 weeks, and 25% in those treated for 4 to 6 weeks (increasing to 91%, 77%, and 50%, respectively, if we include cases with grade 1 uptake and these characteristics). In patients with relapsing/refractory GCA, or who developed GCA having a prior history of PMR, PET-CT positivity reached 54% despite long-term treatment with low-to-moderate doses of GC (68% including cases with a grade 1 uptake).Conclusion: A late 18F-FDG PET-CT (beyond the first 10 days of treatment) can also be informative in a considerable percentage of cases.