What are the main differences between chronic fatigue syndrome and polymyalgia rhumatica?

Shoulder & hip pain: Polymyalgia rheumatica is characterized by hip and shoulder pain/stiffness associated with high inflammatory markers in the blood (sedimentation rate and c-reactive protein). It only occurs in people 50 and older and resolves with steroid treatment within a day or 2. Fibromyalgia is all-over pain that can occur at any age and is not inflammatory. It does not respond to steroids.

Big differences: Polymyalgia rheumatica is a systemic inflammatory disease with association of inflammation in muscle, joints, and even blood vessels in some people. Chronic fatigue is not inflammatory and the exact mechanism is not clear but in some settings may be related to an earlier infections especially viral but sometime it is psychological.