The following is a summary of “Impact of previous glucocorticoid therapy on diagnostic accuracy of [18F] FDG PET-CT in giant cell arteritis,” published in the June 2023 issue of the Seminars in Arthritis and Rheumatism by Narváez et al.

This study aims to determine how prior glucocorticoid (GC) administration affects the diagnostic accuracy of ¹⁸F-FDG PET-CT in giant cell arteritis (GCA). A retrospective analysis of a cohort of 85 GCA patients who received high-dose GC before PET-CT. About 37% of 39 patients previously treated with methylprednisolone (MP) boluses had positive PET-CT (uptakes grade 3 or 2) results. 

The positivity rate was 80% for 125 mg of MP, 33% for 250 or 500 mg, and 0% for 1 g doses. If researchers also classify as positive those cases with grade 1 uptake (with circumferential 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 various MP doses, respectively). PET-CT positivity was 54.5% in patients treated for less than two weeks with high-dose oral GC, 38.5% in those treated for 2 to 4 weeks, and 25% in those treated for 4 to 6 weeks (rising to 91%, 77%, and 50%, respectively, if they include cases with grade 1 uptake and these characteristics). 

PET-CT positivity reached 54% in patients with relapsing/refractory GCA or who developed GCA with a history of PMR despite long-term treatment with low-to-moderate doses of GC (68% including cases with a grade 1 uptake). Often, a late ¹⁸F-FDG PET-CT (after the initial ten days of treatment) can be informative.

Source: sciencedirect.com/science/article/abs/pii/S0049017223000239