Enthesitis related arthritis (ERA) is a subtype of juvenile idiopathic arthritis (JIA) and is associated with the HLA B27 antigen. The International League of Associations for Rheumatology (ILAR) defines ERA using the following criteria: (1) Any patient with both arthritis and enthesitis; (2) the presence of arthritis or enthesitis with two of the following features: Sacroiliac joint tenderness, inflammatory spinal pain, or both; HLA B27 family history in 1st degree relative of medically confirmed HLA B27-associated disease; acute anterior uveitis; onset of arthritis in a boy after the age of 6 yr. Of note, patients with psoriasis or with psoriasis in a 1st degree relative are also excluded.

Juvenile enthesitis-related arthritis

Enthesitis related arthritis, juvenile

Enthesitis-related arthritis

ERA

Juvenile spondyloarthropathy

Enthesitis-related JIA

• The most common presenting symptoms of ERA include arthritis, enthesitis, and symptomatic uveitis.
• With the exception of the hip and sacroiliac joints, a majority of the observed arthritis is peripheral. The most common joints to be affected include the ankles, knees, and hips.
• The observed arthritis is typically asymmetric and typically effects fewer than 4 joints.
• While pain and inflammation about the bones of the midfoot are less common, such symptoms are highly suggestive of the disease.
• As the disease process progresses many patients go on to develop clinical and radiologic evidence of spinal and sacroiliac joint involvement.
• Enthesitis is typically asymmetric and more frequently occurs in the lower extremities.
• Enthesitis most frequently occurs at inferior pole of the patella, the plantar fascia insertion at the calcaneus, and finally the Achilles tendon insertion at the calcaneus. More chronic enthesitis may demonstrate evidence of erosion, calcifications, and heterotopic bone formation on radiographs.
• The anterior uveitis observed with ERA is typically acute in onset and manifests with conjunctival injection, pain, and light sensitivity.

The etiology of ERA is currently unknown; however, the strong association with HLA B27 suggests a genetic component of the disease.

• Other forms of JIA
• Infectious arthritis
• Mixed connective tissue disease
• Leukemia
• Reiter’s syndrome
• Other systemic arthritides

• A thorough history and physical exam are required to diagnose ERA.
• A focused history should include a history of joint and/or enthesitis, back pain, ocular symptoms, and bowel symptoms. One should ensure that the patient does not have a personal or family history of psoriasis as this would exclude the diagnosis of ERA.
• A focused physical exam should be performed to assess for the presence of spinal disease, sacroiliac pain and or instability, joint pain, and enthesitis.

• CBC, erythrocyte sedimentation rate, C-reactive protein, HLA B27
• Antinuclear antibodies, rheumatoid factor, and anticyclic citrullinated peptide antibodies are all typically absent; however, they are used to exclude other differential diagnoses.

• X-ray (Fig. E1) can be used to detect any evidence of arthritic changes (Box 1).
• MRI (Fig. E2) or ultrasound (Fig. E3) may be used to detect and/or confirm sacroiliitis or enthesitis, which can be frequently missed on physical exam in the early stages of the disease.

Physical therapy, heat therapy, and cold therapy can be used to address the musculoskeletal pain associated with the disease.

Acute treatment typically includes monotherapy or combination therapy with NSAIDs and methotrexate/sulfasalazine

If patients are not able to achieve control, of their symptoms with the above regimen, antitumor necrosis factor (anti-TNF) medications such as etanercept and adalimumab

ERA should be managed by a multidisciplinary team including a referral to physical therapy and a certified rheumatologist.

Juvenile Idiopathic Arthritis (Related Key topic)