Arthritic Knee, Inflammation Over Right Thumb, Stiffness, Joint Pain, Negative Bone Scan. Autoimmune Arthritis ?
I assume that you know basics of autoimmune diseases, since your question is very straight forward. I'll revise your knowledge just to ensure that you know everything.
Autoimmune arthritis is a disease characterised by chronic inflammatory response against joints, where body is unable to distinguish between self and non self tissues. Body attacks its own normal tissue resulting in inflammation, pain, stiffness and deformity. It mainly includes Rheumatoid arthritis, Ankylosing spondylosis, Psoriatic arthritis, Sjogrens syndrome besides few more.
I also assume you have undergone other tests before undergoing bone scan to diagnose the particular variety of arthritis. If not, I suggest you do some screening blood tests like RA factor, CRP, ESR, Serum uric acid. Xray and MRI of joints involved also tell us a great deal about the condition of the joint.
One thing you must remember is that there is a difference between age related arthritis and autoimmune arthritis. Age related arthritis will occur after wear and tear of joint cartilage and synovial tissue giving rise to pain stiffness and deformity. Whereas in autoimmune type, pain will come way before you have visible changes. So if your bone scan shows a few changes it need not be conclusive. Bone scan is showing some activity positive for inflammation. That requires clinical correlation.
Your stiffness does sound like one in Rheumatoid or Ankylosing type. Visit your physician and get evaluated for these since treatment is going to be different in both.
If you have reports of previous tests and investigations please share with me for better diagnosis. You have a feature to upload the reports / image by yourself at the right side of the query page, please utilize that so that I can answer your queries better.
If you want help in understanding anything else concerning autoimmune arthritis feel free to ask. I'm available for follow up.
Good day.