Spondyloarthritis

Definition/diagnostic criteria Spondyloarthritis (SpA) is a group of chronic inflammatory rheumatic diseases that primarily affect the axial skeleton, peripheral joints, and entheses. It encompasses conditions such as ankylosing spondylitis (AS), psoriatic arthritis (PsA), reactive arthritis, enteropathic arthritis, and undifferentiated spondyloarthritis.

While specific diagnostic criteria may vary between subtypes, the primary hallmark of SpA is inflammation at the sites of attachment between tendons, ligaments and bone, termed enthesitis. The Assessment of Spondyloarthritis International Society (ASAS) has developed classification criteria for axial and peripheral SpA to aid in diagnosis.

For axial SpA, the key criteria include:

• Chronic back pain of at least 3 months’ duration that improves with exercise and worsens with rest.
• Morning stiffness lasting at least 30 minutes.
• Radiographic evidence of sacroiliitis on imaging or the presence of HLA-B27 antigen.

Peripheral SpA diagnosis involves:

• Inflammatory arthritis, enthesitis or dactylitis.
• Typically asymmetrical involvement.
• Absence of rheumatoid factor and anti-cyclic citrullinated peptide (anti-CCP) antibodies.

Accurate diagnosis is crucial for timely management and preventing long-term disability.

Epidemiology AS is the most common subtype, affecting approximately 0.2-0.5% of the population. It predominantly affects young adults, with an onset typically occurring before the age of 45. Males are more commonly affected than females, with a male-to-female ratio of 2:1. On the other hand, PsA, another common subtype, has a later age of onset and affects both sexes more evenly.

HLA-B27 positivity significantly increases the risk of developing SpA, particularly AS, in genetically predisposed individuals. Environmental factors, such as smoking, are also known to exacerbate the disease.

Diagnosis
Clinical features: Chronic inflammatory back pain, often starting insidiously and improving with exercise, is a cardinal symptom. Enthesitis, especially at the Achilles tendon or plantar fascia, is common. In peripheral SpA, asymmetric oligoarthritis and dactylitis are characteristic. Psoriasis, inflammatory bowel disease, or a history of preceding infection may also provide diagnostic clues.

Investigations include:

1. HLA-B27 testing: HLA-B27 positivity is strongly associated with SpA, especially AS. However, it is not diagnostic on its own, as some HLA-B27-positive individuals do not develop SpA.
2. Imaging: X-rays of the sacroiliac joints can reveal characteristic changes in AS, such as sacroiliitis. Magnetic resonance imaging (MRI) is more sensitive and can detect early inflammatory changes.
3. Blood tests: While there is no specific blood test for SpA, elevated inflammatory markers (e.g., ESR, CRP) may be present during active disease.
4. Clinical assessment: ASAS criteria and expert clinical evaluation should guide diagnosis.

Treatment Treatment strategies for SpA focus on symptom relief, prevention of structural damage, and improving the patient’s quality of life. Non-pharmacological approaches, including physiotherapy and exercise, are essential components of management.

Pharmacological therapy:

• NSAIDs: These are first-line for pain and inflammation control.
• Disease-modifying anti-rheumatic drugs (DMARDs): Methotrexate or sulfasalazine may be used in peripheral SpA, while biologic DMARDs, such as TNF-alpha inhibitors, are effective in refractory cases.
• Pain management: Analgesics and low-dose corticosteroids can provide symptom relief.

Biologics: Biologic therapies like adalimumab and etanercept have revolutionised the management of AS and PsA, offering sustained symptom control and reducing radiographic progression.

Surgery: In severe cases of AS, joint replacement surgery may be necessary.

Prognosis Early diagnosis and appropriate management can greatly improve the long-term outlook for SpA patients. However, SpA is a chronic condition that can lead to significant disability if left untreated. Axial SpA, especially AS, may result in spinal fusion and functional impairment over time. Peripheral SpA, like PsA, can lead to joint deformities and reduced quality of life.