The study will examine the efficacy of a single intramuscular injection of betamethasone dipropionate/betamethasone sodium phosphate at the dose of 20mg/8mg (injection volume 4 ml) as an induction therapy in patients with polymyalgia rheumatica. Twenty patients will be randomized to receive an injection of betamethasone or placebo (isotonic NaCl solution) immediately after diagnosis. Both groups will receive the standard-of-care steroid therapy, starting from 10 mg of prednisone every day (qd), tapered down by 2.5 mg monthly if the disease is not active (scheduled monthly follow-ups by a rheumatologist). Primary outcome measures: the total cumulative dose of glucocorticosteroids and disease duration.