Which of the following is true of psoriatic ahritis –
**Core Concept**
Psoriatic arthritis is a type of spondyloarthritis characterized by inflammation of the joints and skin manifestations of psoriasis. It is a chronic autoimmune disease that affects the joints, skin, and other tissues.
**Why the Correct Answer is Right**
Psoriatic arthritis is associated with the presence of HLA-B27 allele, which is a genetic marker for spondyloarthritis. The disease is characterized by the formation of new bone growth (enthesophytes) around the affected joints, leading to joint damage and deformity. The inflammation in psoriatic arthritis is mediated by the release of pro-inflammatory cytokines, such as TNF-alpha and IL-17, which play a key role in the pathogenesis of the disease.
**Why Each Wrong Option is Incorrect**
**Option A:** Psoriatic arthritis is primarily associated with HLA-A2 allele (Incorrect - HLA-B27 is the correct association).
**Option B:** Psoriatic arthritis is characterized by the presence of rheumatoid factor (Incorrect - RF is more commonly associated with rheumatoid arthritis).
**Option C:** Psoriatic arthritis is a type of osteoarthritis (Incorrect - PsA is a type of spondyloarthritis).
**Clinical Pearl / High-Yield Fact**
Psoriatic arthritis often presents with a "dactylitis" or "sausage finger" appearance, which is a characteristic feature of the disease. This is due to the inflammation and swelling of the entire finger joint.
**Correct Answer: D.**