A 55-year-old woman presents with a 3-month history of bilateral shoulder and hip girdle pain and stiffness, particularly severe in the mornings, lasting over an hour. She finds it difficult to get dressed and rise from a chair. She also reports general malaise and fatigue. Examination reveals restricted active movement of shoulders and hips due to pain, but passive movements are relatively full, and muscle power is normal. ESR is 75 mm/hr. What is the most likely diagnosis?