Is Rheumatoid arthritis a disease of the muscular system?

No Arthritis and Rheumatoid are is not a disease of the muscles. However Arthritis can lead to muscular damage as a result of muscular atrophy as pin stops people from using muscles around affected joints. I have noticed this in my self. I had a total elbow replacement to my right arm, before I had trouble with that arm I was able to lift extremely heavy weights and even the grip of my hand was very strong as a result of RA I started to avoid exerting these muscles, this in turn started them wasting away. now that I have had an elbow replaced which was the main source of the pain I am able to get all of the muscles from the biceps down to the wrist back into some sort of working order. It is understandable that people feel Arthritis may be a muscular disorder , however it is only a disorder that has a secondary affect on muscles.