What is Enthesitis in Psoriatic Arthritis?
Enthesitis is inflammation at the sites where tendons and ligaments insert into bone—a hallmark feature of psoriatic arthritis that can cause pain, functional limitation, and is considered a key pathological site where the disease may initiate 1.
Clinical Characteristics
Enthesitis occurs frequently in psoriatic arthritis, affecting approximately 41.6% of patients overall (67.2% in clinical trials, 27.8% in observational studies) 2. It can present as:
- Painful or asymptomatic inflammation at tendon/ligament insertion sites
- Commonly affected sites: Achilles tendon insertion, plantar fascia insertion, lateral epicondyle, medial femoral condyle
- Associated with dactylitis (sausage digits), which often coexists and indicates worse prognosis 3
Patients with enthesitis demonstrate significantly higher disease activity scores and greater disease burden compared to those without enthesitis 2. This inflammation results from both mechanical stress and immune-mediated processes, particularly involving IL-23-responsive cells producing IL-17A, IL-22, and TNF 1.
Management Approach
Initial Treatment for Unequivocal Enthesitis
For patients with unequivocal enthesitis and insufficient response to NSAIDs or local glucocorticoid injections, therapy with a biologic DMARD should be commenced 4. This is a 2024 EULAR recommendation with high agreement (9.5/10).
The treatment algorithm proceeds as follows:
First-line conservative measures:
- NSAIDs for symptomatic relief
- Local glucocorticoid injections (with important caveats—see below)
- Physiotherapy and lifestyle modifications 5
When conservative measures fail:
- Initiate biologic DMARD (bDMARD), specifically:
- TNF inhibitors
- IL-17A inhibitors (preferred if significant skin involvement)
- IL-17A/F inhibitors
- IL-12/23 or IL-23 inhibitors 4
Critical Considerations for Local Injections
If considering entheseal corticosteroid injections, use extreme caution and follow these principles 5:
- Use only as last resort after NSAIDs, physiotherapy, and rest have failed
- Perform diagnostic ultrasound first to confirm inflammation and rule out tendon rupture
- Prefer perientheseal over intraentheseal injection
- Use ultrasound guidance for needle placement
- Avoid in high-risk patients with existing rupture or structural damage
The evidence for entheseal injections in psoriatic arthritis is limited and mostly expert opinion 5.
Treatment Selection Based on Comorbidities
The choice of biologic should reflect extra-musculoskeletal manifestations 4:
- Clinically relevant skin involvement: Prefer IL-17A, IL-17A/F, IL-23, or IL-12/23 inhibitors
- Uveitis: Use anti-TNF monoclonal antibody
- Inflammatory bowel disease: Use anti-TNF monoclonal antibody, IL-23 inhibitor, IL-12/23 inhibitor, or JAK inhibitor
If Inadequate Response to First Biologic
Switch to another bDMARD or consider JAK inhibitor, including one switch within the same drug class 4. For JAK inhibitors, exercise caution in patients ≥65 years, current/past smokers, cardiovascular risk factors, or thromboembolism risk 4.
Assessment Tools
Enthesitis is typically assessed using validated scoring systems, most commonly the Leeds Enthesitis Index (LEI), which is used in 63.7% of studies 2. Other scores include MASES and SPARCC. Clinical assessment has limitations, and imaging (ultrasound or MRI) can detect subclinical enthesitis but is rarely used in routine practice 6.
Common Pitfalls
- Delaying biologic therapy: Don't persist with NSAIDs alone if enthesitis remains active—this leads to ongoing inflammation and structural damage
- Injecting without imaging: Blind entheseal injections risk tendon rupture and may miss the actual site of inflammation
- Ignoring skin disease severity: This should guide your choice of biologic agent
- Treating enthesitis in isolation: Remember this is part of a systemic disease requiring comprehensive management