Medicine – Common Features of Seronegative Spondyloarthritides

The seronegative spondyloarthritides, now more commonly grouped under the term spondyloarthritis, are a family of inflammatory rheumatic disorders that share a number of clinical, radiological, and genetic features. This group includes conditions such as ankylosing spondylitis, psoriatic arthritis, reactive arthritis, and arthritis associated with inflammatory bowel disease. Although each disease has its own characteristic presentation, there is substantial overlap between them.

1. Negative Rheumatoid Factor

A defining laboratory feature is the usual absence of rheumatoid factor (RF), which is why these conditions are traditionally described as seronegative. This helps distinguish them from rheumatoid arthritis, although a negative RF alone is not sufficient to make the diagnosis.

2. Asymmetrical Inflammatory Peripheral Arthritis

Peripheral joint involvement often takes the form of an asymmetrical inflammatory oligoarthritis, meaning that only a few joints are affected and the distribution is uneven between the two sides of the body. The lower limbs are commonly involved, particularly the knees and ankles. Affected joints may become painful, swollen, warm, and stiff.

3. Radiological Sacroiliitis

Sacroiliitis is an important radiological feature, especially in axial forms of spondyloarthritis. Imaging may show inflammation, erosions, sclerosis, joint-space narrowing, and eventually fusion of the sacroiliac joints. In early disease, MRI can demonstrate active inflammation before definite abnormalities become visible on plain radiographs.

4. Spondylitis

Inflammation of the spine, or spondylitis, is another characteristic feature. Patients may experience inflammatory back pain, typically with morning stiffness and improvement after activity rather than rest. Progressive spinal inflammation can eventually lead to reduced mobility and structural changes.

5. Enthesitis

Enthesitis refers to inflammation at the sites where tendons, ligaments, or joint capsules attach to bone. It is a hallmark of the spondyloarthritis group and commonly affects the Achilles tendon insertion and plantar fascia. Patients may present with heel pain or tenderness at other entheses.

6. Association with HLA-B27

There is a strong genetic association with HLA-B27, although the frequency varies between the different spondyloarthritides and between populations. The association is particularly strong in ankylosing spondylitis, where older teaching sources often quote a prevalence of around 90–96% in affected individuals of certain ethnic backgrounds.

7. Anterior Uveitis

Anterior uveitis is an important extra-articular manifestation and may occur in several forms of spondyloarthritis. It usually presents with an acutely painful red eye, photophobia, and blurred vision. The inflammation often affects one eye at a time and may recur, especially in HLA-B27-associated disease.

8. Clinical Overlap Between the Disorders

A significant feature of the seronegative spondyloarthritides is the clinical overlap between the individual diseases. For example, a patient may have axial inflammation together with peripheral arthritis, enthesitis, uveitis, psoriasis, bowel inflammation, or a history of preceding infection. Because of this overlap, classification is often based on the predominant pattern of disease rather than completely separate and rigid categories.

Key Clinical Pattern

The common pattern can be remembered as RF negativity, asymmetrical inflammatory arthritis, sacroiliitis, spondylitis, enthesitis, HLA-B27 association, and anterior uveitis, with considerable overlap between the different disorders in the spondyloarthritis spectrum.