423tis, which have been shown to be inaccurate, MSUS has the advantage of being able
to directly visualize disorders of the enthesis as well as entheseal-related structures.
This may appear as hypoechogenic thickening of the enthesis with or without
Doppler signal, enthesial erosion, entesophytes, calcifi cations, cortical irregulari-
ties, or bursitis and tendonitis [ 31 ]. These infl ammatory and structural disorders
have been encompassed, years ago, in the OMERACT ultrasound defi nition of ente-
sopathy [ 5 ]. A defi nition of active enthesitis should denote potentially reversible
MSUS disorders and perhaps ongoing disease severity, analogous to active synovi-
tis in rheumatoid arthritis. Recently OMERACT reported the fi rst consensus-based
US defi nition of enthesitis and its elementary components to ensure a higher degree
of homogeneity and comparability [ 32 ]. There was agreement on the inclusion of
hypoechogenicity, increased thickness at the tendon insertion, calcifi cations, enthe-
sophytes, erosions, and Doppler activity as elementary lesions of enthesitis.
Whereas, there was no agreement obtained regarding the inclusion of bursitis or
tendonitis. Furthermore, the consensus delineated signs of active infl ammation from
signs of structural damage at the enthesis site, where hypo-echogenicity, thickening,
and Doppler signal represent the main signs of active enthesitis.
Subclinical enthesitis was reported in earlier MSUS studies, which revealed a
high frequency of abnormalities in asymptomatic patients with psoriasis without
musculoskeletal clinical signs or symptoms [ 33 , 34 ]. In concordance, it was also
reported in both early [ 35 – 37 ] and established SpA including psoriatic arthritis [ 31 ,
38 – 40 ]. Recently EULAR published the fi rst recommendation of MSUS-imaging in
the diagnosis and management of SpA in clinical practice based on the best avail-
able evidence and clinical expertise supported by an international panel of experts
[ 41 ]. When peripheral SpA is suspected, MSUS is advised to detect peripheral
enthesitis, which may support the diagnosis of SpA. It also recommends the use of
US to monitor disease activity (particularly synovitis and enthesitis) in peripheral
SpA, providing additional information on top of clinical and biochemical
assessments.
Several MSUS enthesitis assessment tools have been developed in SpA cohorts
for diagnosis and classifi cation as well as for monitoring response to treatment [ 39 ,
42 – 44 ]. The Glasgow Ultrasound Enthesitis Scoring System (GUESS) tool is a
semiquantitative GS 5 enthesial site scoring system (Achilles, quadriceps, superior
and inferior patellar tendons, and plantar fascia) [ 42 ]. The Madrid Sonographic
Enthesitis Index (MASEI) is a semiquantitative GS and PD 6 enthesial site scoring
system (triceps, Achilles, quadriceps, superior and inferior patellar tendons, and
plantar fascia) [ 39 ]. MASEI scores bone erosions, power Doppler signal, and severe
enthesophytes higher than tendon thickening, hypo-echogenicity, or small entheso-
phytes. MASEI performed well for diagnosis and classifi cation [ 41 ]. Both scoring
systems have shown good reproducibility [ 45 ].
While the role of the enthesis is fully appreciated in SpA, there are some recent
fi ndings pointing toward similar novel mechanisms of synovitis and joint damage in
osteoarthritis that have previously been unacknowledged [ 46 , 47 ]. Normal enthesis
fi brocartilage shows age-related changes similar to osteoarthritis, including fi ssur-
ing, fi brillation, and degeneration. Therefore, the term “enthesopathy” is recom-
18 PROMs and Musculoskeletal Ultrasonography