Reactive Arthritis¶

Definition¶

Reactive arthritis (formerly Reiter syndrome) is a seronegative spondyloarthropathy that develops following a genitourinary (Chlamydia trachomatis) or gastrointestinal (Salmonella, Shigella, Campylobacter, Yersinia) infection. The classic triad is arthritis, urethritis, and conjunctivitis, though the complete triad is present in only a minority of patients. Spinal involvement occurs in a subset of cases.

Imaging Findings¶

Sacroiliac Joints¶

Sacroiliitis — often asymmetric or unilateral (similar to psoriatic arthritis)
Erosions, sclerosis, and widening

Spine¶

Non-marginal, bulky, asymmetric syndesmophytes (similar to psoriatic spondyloarthropathy)
Skip-level involvement
Less common and less severe than in AS

Peripheral Joints¶

Asymmetric oligoarthritis, predominantly lower extremity
Enthesitis (Achilles tendon, plantar fascia)
Dactylitis ("sausage digits")

Clinical Pearl

Reactive arthritis, psoriatic spondyloarthropathy, and ankylosing spondylitis can all produce sacroiliitis and syndesmophytes. The pattern helps distinguish them: AS has symmetric sacroiliitis with marginal syndesmophytes; psoriatic and reactive arthritis have asymmetric sacroiliitis with non-marginal syndesmophytes. Clinical context (preceding infection, skin changes, eye involvement) provides additional diagnostic information.

Key Points¶

Seronegative spondyloarthropathy triggered by GU or GI infection
Asymmetric sacroiliitis and non-marginal syndesmophytes (similar to psoriatic)
Classic triad: arthritis, urethritis, conjunctivitis
HLA-B27 positive in 60–80%
Spinal involvement is less common and less severe than in AS

References¶

Cheeti A, Chakraborty RK, Ramphul K. Reactive Arthritis. In: StatPearls. Treasure Island (FL): StatPearls Publishing; updated 2023 Jan 2. https://www.ncbi.nlm.nih.gov/books/NBK499831/
Reactive arthritis. Radiopaedia.org. https://radiopaedia.org/articles/reactive-arthritis
Chang EY, Chen KC, Huang BK, Kavanaugh A. Adult Inflammatory Arthritides: What the Radiologist Should Know. RadioGraphics. 2016;36(6):1849-1870. https://pubmed.ncbi.nlm.nih.gov/27726745/
Giraudo C, Astorri D, Reijnierse M. Reactive arthritis: a comprehensive journey through diagnostic findings. Skeletal Radiol. 2025;54(11):2443-2455. https://pubmed.ncbi.nlm.nih.gov/40473988/
Jubber A, Moorthy A. Reactive arthritis: a clinical review. J R Coll Physicians Edinb. 2021;51(3):288-297. https://pubmed.ncbi.nlm.nih.gov/34528623/
Klecker RJ, Weissman BN. Imaging features of psoriatic arthritis and Reiter's syndrome. Semin Musculoskelet Radiol. 2003;7(2):115-126. https://pubmed.ncbi.nlm.nih.gov/12920649/
Expert Panel on Musculoskeletal Imaging, et al. ACR Appropriateness Criteria® Inflammatory Back Pain: Known or Suspected Axial Spondyloarthritis: 2021 Update. J Am Coll Radiol. 2021;18(11S):S340-S360. https://pubmed.ncbi.nlm.nih.gov/34794593/