This sounds like an inflammatory arthritis which could be one of the autoimmune arthritis disorders or as simple as the "reactive" arthritis sparked by several common viruses. It would be an EXTREMELY unlikely presentation of MS. Very, very unlikely. He should see his doc and be checked for the diseases which cause arthritis, including strep, hepatitis, rheumatoid arthritis, etc. Also, joint pain can be caused by meds.
The possibilities are so numerous it would be silly to go into them here. Again, MS does not present with primary joint pain, especially if the joints are swollen, tender and/or red.
MS does cause joint pain by a secondary action of altering the muscular action on the joints or of paresthesias that appear to involve the joints, but arthritis (warm, swollen, tender joints) is not a part of MS. If he has no swelling, warmth or redness over the joints, but he does have pain with bending the joints then he has joint pain called "arthralgias." This is most likely due to an infection, but he should still have all the blood work done.
I guess I have written this presuming he does not already have MS and you posted here for fear that he might. If he does have MS, then I still suspect another disorder (because arthritis is not a part of MS, per se) and people with MS can get all the other disorders of life, too. It's not fair, but true.
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