Background Enthesitis is a frequent feature of psoriatic arthritis (PsA). Osteoarthritis (OA) shares many features with PsA including DIP, PIP, neck and spinal involvement, lower limb large joint arthropathy and enthesopathies including trochanteric bursitis and lateral epicondylitis.
Objectives In this study we tested the hypothesis that a similar ultrasound (US) determined enthesopathy load existed in PsA and OA.
Methods Twenty-four patients with PsA, 25 with OA and 28 healthy controls (HC) were recruited. The clinical assessments were performed by the same clinician unaware of the US assessments. Patients with PsA were chosen consecutively if they did not have any psoriatic lesions at the lower limbs to provide blindness for the ultrasonographer and with no suspicion of OA clinically. OA patients and healthy controls did not have any history of psoriasis and HC did not have any knee pain. The major enthesis of the lower limbs (Quadriceps, patellar tendon origin and insertion, Achilles and plantar fascia, bilaterally) were scanned by US for abnormalities related to inflammation (hypoechogenicity, thicknening, Doppler, bursal effusion) and chronicity (calcifications, enthesophytes and erosions) semiquantitavely on a scale between 0-3. The overall US scores were calculated by adding each finding. The US was performed blinded to diagnosis.
Results All three groups were matched for body mass index (BMI) (mean (SD) values in HC, OA and PsA respectively: 28.7 (5.4), 30.3 (3.9), 29.3 (5.4)). Patients with PsA (53.5 (6.1)) and OA (52.8 (1.1) were older than HC (41.3 (9.8)). PsA patients had higher US scores than HC (p<0.001 for inflammation, chronicity and overall scores) (table 1). OA patients also had higher US scores than HC (p value for inflammation: 0.003; chronicity: 0.017; overall: 0.001). The difference between PsA and OA did not reach significance. ANCOVA was performed to control for age, gender and BMI, which showed that only PsA group had higher US scores then HC (p value for inflammation: 0.03; chronicity: 0.05; overall: 0.017) which could not be shown in OA vs PsA and HC.
The BMI was significantly correlated to US scores of enthesopathies in OA (R=0.451; p=0.03) but not in PsA or HC. On the other hand, age was correlated to US scores only in PsA (R=0.609; p=0.002), but not in OA or HC.
Conclusions This study shows that enthesopathies are also frequent in OA, similar to PsA. BMI was more important in OA and age in PsA. These findings are important for the assessment of the relevance of sonographic determined enthesopathy in a patient with psoriasis and OA.
Disclosure of Interest None declared