High prevalence of ultrasound-defined enthesitis in patients with metabolic syndrome. Comment on: How normal is the enthesis by ultrasound in healthy subjects? Di Matteo et al.

Sirs, We read with great interest the paper recently published in your journal by Dr Di Matteo and colleagues, in which they tested the recent Outcome Measures in Rheumatology (OMERACT) definition for the ultrasound (US) diagnosis of enthesitis in healthy subjects questioning the possibility of a low discriminant power of the above cited definition (1). This US definition requires entheseal inflammatory abnormalities, while ipervascularisation and structural damages are not mandatory (2). The authors evaluated various lower limb entheses of 82 healthy subjects with US applying OMERACT’s filter to diagnose “active” enthesitis (entheseal thickening, hypoechogenicity and power Doppler signals). The results of the study demonstrated a high prevalence of signs of “active” enthesitis (in 34.1% out of 82 subjects, and in 8.4% out of 820 entheses) and a correlation with age and body mass index (BMI) (1). These prevalences are comparable or higher than the prevalences reported in previous studies in which different US definitions of enthesitis were applied, thus questioning the discriminant power of the recent OMERACT’s US definition of enthesitis (3-5). In this context we are applying the above cited OMERACT US definition of enthesitis on various groups of patients, with the aim to compare the prevalences of enthesitis in different pathologies. Here we report preliminary data about US-defined enthesitis in patients with metabolic syndrome. A group of 50 consecutive outpatients visited for mechanical low back pain, between February 2019 and September 2019 in Rheumatology Unit of Siena (20 males, 30 females, mean age 58 years) and all fullfilling International Diabetes Foundation (IDF) criteria for metabolic syndrome (6), were also evaluated with multi-site bilateral US entheseal examination (shoulders, elbows, hips, knees and heels) by an expert rheumatologist sonographer, blinded to the patient’s conditions. Each patient underwent bilateral dynamic B-mode and power Doppler (PD) US examination of twelve entheseal sites: acromial deltoid insertion, supraspinatus, lateral and medial elbow epicondyles, triceps, trochanteric enthesis, quadriceps and patellar tendon, ileo-tibial tract, Achilles tendon and plantar fascia. US was performed using Esaote MyLab Twice machine equipped with 6–18 MHz transducer and standardised B-mode and Doppler settings, which were optimised for all examinations. Doppler parameters were pulse repetition frequency within 500–750 Hz and Doppler frequency within 7–11.1 MHz. An enthesis was studied as the 2 mm zone of soft tissue adjacent to the bone cortex, based on OMERACT’s filter (2). Enthesitis was defined, for each site, when only mandatory inflammatory lesions (enthesis thickening and hypoechogenicity) were present. Power Doppler (PD) intra-entheseal signal was recorded as sign of active enthesitis. Structural abnormalities (erosions, enthesopytosis/ calcification) were also recorded. Inflammatory and structural changes were scored as a whole when present (score 1) or absent (score 0). The sum of entheses with inflammatory and structural damage was recorded and defined as “global inflammatory score” and “global structural damage score” for each patient. The prevalences of enthesitis