Paediatrics: Enthesitis-related arthritis

Enthesitis-related arthritis

Recently introduced ILAR terminology and category.¹ Previously known as juvenile ankylosing spondylitis or seronegative spondyarthropathy. Characterized by arthritis with enthesitis (inflammation in any tendinous, ligamentous, or muscular insertion on to bone) or arthritis alone or enthesitis alone with 2 of the following features:

•   sacroiliac joint tenderness;

•   inflammatory spinal pain;

•   HLA B27 +ve;

•   first degree relative family history of uveitis;

•   age of onset 6 >yrs.

Exclude RF +ve; systemic arthritis; psoriasis in patient or first degree relative.

Clinical features

•   Commonly adolescent or pre-adolescent boys (M:F, 10:1).

•   Oligo- or polyarthritis predominantly in lower limbs.

•   Enthesitis especially around the foot (heel pain). Children can present with isolated heel pain many years before spinal symptoms.

•   Spinal pain may not be present at onset.

•   Progresses to sacroiliac joint tenderness, inflammatory spinal pain, or buttock pain (worse at night plus early morning stiffness).

•   Systemic features: low grade fever, weight loss, and fatigue.

•   Acute anterior uveitis (10–15%): acutely painful red, photophobic eye—different from uveitis seen with other JIA.

•   Associated IBD and reactive arthritis.

Examination

•   Examine affected joints: for synovitis, effusions, associated muscle wasting, and range of movement.

•   Spine examination: is essential. Test for cervical rotation, thoracic rotation, lateral flexion, and document the Schober test (mark 10cm above and 5cm below the ‘dimples of Venus’ and note the increase gained by forward flexion). Normal is at least 21cm—varies little with age and gender. Look for loss of normal lumbar lordosis.

•   Chest expansion: may be reduced in advanced disease.

•   Examine commonly affected enthesitis sites around the heel: Achilles insertion and calcaneum.

Investigations

•   FBC (normochromic anaemia, mild leucocytosis, and thrombocytosis).

•   If microcytic anaemia think of occult IBD.

•   CRP may be raised.

•   RF and ANA negative.

HLA B27 +ve 90%, but also +ve in 8–10% of normal population.

Radiology

X-ray changes lag behind clinical symptoms by up to 10yrs. MRI is the gold standard in adults. Interpretation is difficult in children. Lateral views may show Romanus lesions (small erosions of the corners of the vertebral bodies).

X-rays

• Affected joints: soft tissue swelling, periarticular osteopenia, erosions, joint space narrowing, bony ankylosis.

• Heel may show calcaneal spur or fluffy exostoses on Achilles.

• Sacroiliac joints may show erosions, sclerosis, and fusion.

Thoracolumbar junction may show bony overgrowth syndesmophytes.