Polymyalgia rheumatica (PMR) is the most common chronic inflammatory rheumatic disease among the elderly and is characterized by proximal extremity pain and fatigue. Treatment with prednisolone carries several significant adverse effects, and it is therefore essential to avoid unnecessary treatment. However, clinical diagnosis and even imaging such as positron emission tomography and computed tomography (PET/CT) has low diagnostic accuracy, which decrease after start of prednisolone. The purpose is to evaluate a new method to diagnose PMR with PET/CT using magnetic resonance imaging (MRI) for informing the interpretation of PET in 111 patients suspected of PMR at baseline and after 8 weeks prednisolone treatment. In addition, a treatment initiation strategy guided by clinical diagnosis combined with PET will be evaluated in 100 patients with newly diagnosed PMR.