What is the most common inflammatory disease of the axial skeleton?

• A. Seronegative Spondyloarthropathies
• B. Gout
• C. Ankylosing Spondylitis
• D. Rheumatoid Arthritis

Answer: (C)

Ankylosing Spondylitis is the most common inflammatory disease involving the spine and sacroiliac joints. It typically begins in late adolescence or early adulthood and presents with inflammatory back pain—pain and morning stiffness that persist for months and improve with activity or NSAIDs. Over time, inflammation can lead to structural changes such as sacroiliitis and eventual fusion of the spine, giving a “bamboo spine” appearance on imaging due to syndesmophyte formation. A strong association with HLA-B27 helps explain the axial predilection. Extraskeletal features like anterior uveitis, enthesitis (such as at the Achilles tendon), inflammatory bowel disease, and psoriasis can accompany the condition. This makes it the best answer when the focus is on inflammatory disease of the axial skeleton, distinguishing it from gout (peripheral, crystal-related) and rheumatoid arthritis (predominantly peripheral joint involvement with different serology). Seronegative spondyloarthropathies is the broader group that includes Ankylosing Spondylitis, but Ankylosing Spondylitis is the most common axial inflammatory disease within that group.