Predictive Factors for Treatment Response in Patients With Newly-diagnosed Polymyalgia Rheumatica and Giant Cell Arteritis

Biological material will be sampled at three time-points. The first time-point will be when patients have been treated with 15 mg of prednisone per day for at least 5 days. A second time-point will be after prednisone was successfully tapered and maintained at 5 mg per day for at least 5 days, a third time point will be 4 weeks after the stop of prednisone. Biosampling is done for cellular analyses, pharmacokinetics and hormone measurements.

Concentrations of GC, MC, androgens and progestins will be determined and the suppression of cortisol and cortisone upon prednisone treatment will be analyzed.

The time to first relapse, the cumulative steroid dose at 1 year after diagnosis, the need for treatment with steroid sparing agents and the GTI after 1 year will be correlated to the percentage of in vitro inhibition of cytokine concentration by dexamethasone treatment, to the prednisone/prednisolone ratio in plasma, to the percentage of endogenous GC suppression (plasma and urinary cortisol and cortisone) by prednisone treatment. Furthermore, correlations of steroid sensitivity with Mineralocorticoid (MC) and androgens will be investigated.

Plasma concentrations of prednisone and its active metabolite prednisolone will be quantified by liquid chromatography-tandem mass spectrometry (LC-MS/MS). If changes on prednisone/prednisolone are observed, the quantification of the 6-hydroxylated prednisone/prednisolone metabolites in 24 h urine samples will be performed to estimate their metabolism as well as the ratio of inactive to active GC.