I think prednisone plays a role since it reduces the inflammation causing the PMR pain. Here's the more technical answer 🙂

"Prednisolone works by blocking the effects of certain chemicals that cause inflammation inside your body. It does not cure polymyalgia rheumatica, but it can help relieve the symptoms. When used to treat polymyalgia rheumatica, prednisolone is taken as a tablet." -- Polymyalgia rheumatica - Treatment - NHS: https://www.nhs.uk/conditions/polymyalgia-rheumatica/treatment