25th February 2025

Investigation of spondyloarthropathies

Bloods will often show a raised ESR and CRP, but negative RF and ACCP (anti-citrullinated protein) antibodies. 

In reactive arthritis genitourinary and stool cultures should be taken, but are often negative.

Imaging may include: 

• Pelvic (AP) and spinal X-rays showing sacroiliitis with sclerosis and erosions. Persistent sacroiliitis and enthesitis cause bony growth with syndesmophytes (spurs) and intervertebral ligament calcification. There is eventual ankylosis (fusion) of the sacroiliac and spinal facet joints (‘bamboo spine’).
• MRI can show sacroiliitis not seen on X-ray.
• Hands and feet X-rays in PsA, which may show erosion of the DIPJs (‘pencil-in-cup appearance’) with periarticular bone formation.

Box 1 Distinguishing spondyloarthropathies from rheumatoid arthritis