Unoftunately i don't know the exact answer of that question, and I may guess that only doctors may know it for sure. But I may add, that the erosion in OA causes inflamation, and for RA is the opposite the inflamation causes erosion, and when erosion is already present in RA heppens the double trouble.
Iris, i'll ask you a simple question. To you have marked difference in the joint 'problems' durring weather changes ?