CASE 4: Psoriatic arthritis

In this case the erosions and the cartilage loss are predominantly in the DIP rather than in the MCP joints. There is much more indistinct proliferative change around the erosions than in the last case, in which the erosions were more clearly defined. All of these features are typical of psoriatic arthritis. Psoriatic arthritis may present long before the skin lesions do, and therefore psoriasis need not be present for you to make a diagnosis of psoriatic arthritis.

In the elbows of this patient, instead of discrete erosions there are bony proliferations at the insertions of ligaments, tendons, and joint capsules (called entheses). The proliferations are known as enthesophytes. These fuzzy cortical responses may obscure the erosions that originally caused them. They are common in psoriatic arthritis. Rheumatoid arthritis usually does not exhibit such profound reactive change.