We aimed to compare the prevalence of enthesopathy seen on ultrasonography (US) in spondyloarthritis (SpA) and rheumatoid arthritis (RA) and compared it to healthy controls.

All included patients with RA (2010 ACR/EULAR criteria) and SpA (ASAS criteria) and healthy controls underwent clinical and US evaluation of enthesis at seven sites (quadriceps, proximal and distal patellar, Achilles and triceps tendons, plantar aponeurosis and lateral epicondyle enthesis). The Glasgow Ultrasound Enthesitis Scoring System (GUESS) and the Madrid Sonographic Enthesitis Index (MASEI) scores were determined by two sonographers blinded to clinical data.

We included 30 patients with RA (mean age: 55.7±14.8 years, mean disease duration 10.5±7.9years); 41 with SpA (mean age: 45.3±15.4 years, mean disease duration 9.2±8.7years) and 26 healthy controls (HC) (mean age: 50.4±17.3years). Patients with SpA and RA had similar prevalence of painful enthesis of examined sites (17% vs. 14%, non-significant [ns]), but more than among in healthy controls (3%, P<0.05 for RA and SpA comparison). Comparison between SpA and RA patients revealed that at least one US enthesis abnormality was found with similar frequency (46% and 48% sites [ns]) but both rheumatic diseases had higher frequency of US enthesis abnormality than HC (31%, P<0.05 for RA and SpA comparison). The mean MASEI score was 8.5±7.3 for RA patients, 7.8±6.5 for SpA patients (ns) and 3.4±2.8 for healthy controls (P<0.05 for RA and SpA comparison). Overall, 6 RA (20%) and 4 SpA (10%) patients had a MASEI score≥18 (ns). None of the healthy controls had a MASEI score≥18 (P<0.05 for RA and SpA comparison). The mean GUESS score was 5.8±3.1 and 6.3±3.9 for RA and SpA patients (ns), and 4.0±3.1 for healthy controls (P<0.01 vs. SpA and <0.05 vs. RA).

RA and SpA patients did not differ in entheseal abnormalities seen on US. Such US features may have low specificity in inflammatory conditions affecting joints and enthesis such as SpA and RA.