Background In patients with seronegative rheumatoid arthritis (RA) there is a difficulty to make the differential diagnosis with the spondyloarthropathies.

Objectives To assess the presence of enthesitis in patients with seronegative RA in comparison with the healthy controls (HC), patients with seropositive RA and ankylosing spondylitis(AS).

Methods In this cross-sectional study, seronegative and seropositive RA patients, who fulfilled the 2010 ACR/EULAR criteria, patients with AS and HC have been assessed by grey scale and power doppler ultrasonography for the presence of enthesopathy at the achilles tendon, plantar fascia, proximal patella, distal patella, quadriceps, tibialis anterior, triceps, common flexor and extensor tendons. Clinical assessment of the patient groups included demographic findings, health assessment questionnaire and DAS28.

Results In our study, we recruited age and sex matched 27 seronegative RA, 19 healthy controls, 24 seropositive RA and 23 ankylosing spondylitis patients. We evaluated and analysed both right and left sides of the enthesis regions separately which have been indicated in the methods section. The mean DAS28, mean ESR and mean CRP of the patients with seronegative RA were 3.6±1.28, 32.2±21.2 and 12.37±27.77 respectively (table 1).

Median of Madrid sonographic enthesitis index (MASEI) was 5 in patients with seronegative RA. 4 patients have severe scores (MASEI score ≥20). There were significant differences between seronegative RA and healthy controls (MASEI score:3), (p=0.014) but no differences has been observed between seronegative RA with seropositive RA (MASEI score:6) and anklosing spondylitis (MASEI score:7) in MASEI scores.

In comparison, hypoechogenicity of quadriceps tendon (16 (29.6%) vs 6 (12.5%), p=0.037), bone erosion at the quadriceps tendon attachment (9 (16.6%) vs 0, p=0.003), calsification at achilles tendon (17 (31.4%) vs 6 (12.5%), p=0.023) have been observed more frequently in patients with seronegative RA than seropositive RA. Significantly higher number of patients with bone erosion at the common extansor tendon (26 (48.1%) vs 3 (6.5%), p=<0.001), calsification at achilles tendon (17 (31.4%) vs 2 (4.3%), p=0.024), erosion at triceps tendon (13 (24%) vs 1 (2.1%), p=0.035) have been detected in patients with ankylosing spondylitis than seronegative RA (table 2).

Conclusions We observed that enthesis involvement was not seldom in patients with seronegative RA. Furthermore there were also similar frequency of entesis involvement in seropositive patients with RA. The value of enthesis sites evaluation for the differential diagnosis of patients with seronegative RA should be further investigated and the assessment of enthesis sites in seronegative and seropositive RA patients can be important to detect active and chronic changes at the enthesis region.

Disclosure of Interest None declared