A 70-year-old woman presents with a 6-month history of bilateral aching and morning stiffness in her shoulders and hips, making it difficult to get dressed or rise from a chair. The stiffness lasts over an hour. She also feels generally fatigued and has lost some weight. Examination reveals tenderness over the shoulder and hip girdles with reduced active range of movement, but no joint swelling. Her ESR is 75 mm/hr and CRP is 60 mg/L. What is the most likely diagnosis?