They have some overlap, but are TOTALLY different fields. Sure, both can treat MSK, but PM&R is more focused on soft tissue, while rheumatology is mostly joint related. However, the bulk of rheumatology is treating AUTOIMMUNE diseases such as lupus, rheumatoid, sjogren's, ankylosing spondylitis, vasculitis, psoriatic arthritis, etc. PM&R, on the other hand, is more focused on rehabilitation after SCI, TBI, etc.