**Question:** All are features of seronegative spondyloarthropathies except -

A. Ankylosing Spondylitis (AS)
B. Reactive arthritis (ReA)
C. Psoriatic arthritis (PsA)
D. Enthesitis-related arthritis (ERA)

**Core Concept:** Seronegative spondyloarthropathies are a group of inflammatory rheumatic diseases characterized by involvement of the axial skeleton (spine and sacroiliac joints) and extra-articular manifestations. They are generally seronegative for rheumatoid factor and antinuclear antibody.

**Why the Correct Answer is Right:** D. Enthesitis-related arthritis (ERA) is a distinct subgroup within the seronegative spondyloarthropathies that is characterized by enthesitis (inflammation at the site of attachment of a tendon, ligament or joint capsule to bone). ERA predominantly affects children and young adults and has an association with genetic factors (HLA-B27). Since ERA is part of the seronegative spondyloarthropathies, it cannot be considered as an exception.

**Why Each Wrong Option is Incorrect:**

A. Ankylosing Spondylitis (AS) is a seronegative spondyloarthropathy characterized by inflammation of the spine, sacroiliac joints, and extra-articular manifestations like uveitis, inflammatory bowel disease, and psoriasis. AS is indeed a seronegative spondyloarthropathy.

B. Reactive arthritis (ReA) is a seronegative spondyloarthropathy that develops secondary to a preceding gastrointestinal, urinary, or sexually transmitted infection. Although ReA is also a seronegative spondyloarthropathy, the question asks for a feature that is not a part of seronegative spondyloarthropathies, which ReA is.

C. Psoriatic arthritis (PsA) is a seronegative spondyloarthropathy characterized by psoriasis and is associated with the HLA-B27 allele. PsA is indeed a seronegative spondyloarthropathy, making it incorrect as an exception to the seronegative spondyloarthropathies.

**Clinical Pearl:** The term "seronegative" in the context of spondyloarthropathies refers to the absence of rheumatoid factor and anti-citrullinated peptide antibodies in the patient's serum. This distinguishes seronegative spondyloarthropathies from rheumatoid arthritis, which is seropositive for rheumatoid factor and anti-citrullinated peptide antibodies.

**Why Each Wrong Option is Incorrect:**

A. Rheumatoid arthritis (RA) is a seropositive autoimmune disorder characterized by symmetric synovitis affecting small joints, autoantibodies, and extra-articular manifestations like lung, heart, and eye involvement. RA is not a seronegative sp