A 53-year-old patient experiences severe thumb pain without involvement of other fingers. What is the most likely diagnosis?

The most likely diagnosis for a 53-year-old patient experiencing severe thumb pain without involvement of other fingers is osteoarthritis. This condition commonly affects the joints of the hands, particularly the base of the thumb, leading to localized pain and stiffness.

Osteoarthritis is characterized by the degeneration of cartilage and changes in the bone, causing pain that often worsens with activity and improves with rest. In addition, it typically presents with joint swelling and tenderness, but in this case, the isolated pain in the thumb aligns well with the pattern often seen in osteoarthritis.

Other conditions such as rheumatoid arthritis usually involve multiple joints symmetrically and lead to systemic symptoms, while hemochromatosis typically causes joint pain in the hands among other systemic symptoms but is less commonly the sole presentation. Pseudogout, caused by the deposition of calcium pyrophosphate crystals, can affect various joints, but the presentation often includes more than just the thumb and is characterized by acute flare-ups rather than persistent pain. Therefore, given the isolated nature of the thumb pain in this age group, osteoarthritis is the most fitting diagnosis.