My Dad Is 89. He Recently Began Experience A Sudden

My dad is 89. He recently began experience a sudden onset of extreme pain in his right arm. The pain normally occurs at night; wakes him up; and runs from the tip of his middle finger up through his shoulder. He has seen a dr. and tests revealed that he does NOT have rheumatoid arthritis. This was a fairly sudden thing...any ideas of what kind of arthritis it might be? So far, nothing has effectively relieved the pain.