My 69 Year Old Brother Has Had Severely Swollen Hands

My 69 year old brother has had severely swollen hands and wrists for one month. Doctors have tested for RM arthritis and gout. He has neither. He is in severe pain night and day. Just got put on predisone, but doctors don't know what it is. His hands look like giant swollen clubs. It takes two hands to lift a glass, he can't even pull a sheet up during the night when it it needed. Any suggestions what to test for next? Thank you!