Hi, and a welcome from me, too. Since you are so new to this forum I don't know how long you have been considering MS as a possibility. If it is just because of the onset of these "parethesias", I will echo what JJ said above. While 5% of MS presents after the age of 50, it does become more unusual as one ages. That said, it is possible. And it would be the height of bad luck to have RA, psoriatic arthritis AND MS, but we have had some people here with enormously bad luck.
I want to make two points here. The sensation you are describing - that of an invisible internal tremor in a muscle - is indeed a neurologic problem. Many here have complained of it. I had it early in my MS and I knew it wasn't normal. My neuro didn't seem to think much of it. I doubt a PCP or a Rheumatologist would be aware of it. But, now you are having other paresthesias. You might want to read the Health Page on Paresthesias:
http://www.medhelp.org/health_pages/Multiple-Sclerosis/Paresthesias---Things-That-Go-BUZZ-in-the-Night/show/378?cid=36
The second is not one you want to hear, I suspect. Embrel is in a class of drugs called "anti-TNF agents". TNF stands for Tumor Necrosis Factor and it is a part of the immune surveillance system. Other anti-TNF drugs include Humira and Remicade and there are a few others..
There have been several reports in the literature that link anti-TNF drugs to the onset or exacerbation of MS. It isn't clear to me that this is a common thing, but I have found several sources that advise that people with MS or who are suspected of having MS NOT take an anti-TNF drug unless the benefit greatly outweighs the risk. If anyone like I will provide the sources for this info.
You should see a neurologist if these sensations continue or increase. I realize that I am suggesting something that is less likely than not, but the association between anti-TNF and MS is a known thing and you are now having neurologic symtpoms. I do not know if Embrel and its siblings cause neuropathy - if so, I'm not aware of it. Did you take methotrexate before the Embrel?
Quix