Enthesitis in Spondyloarthritis on Ultrasound: OMERACT Definitions and MASEI Index
Ultrasound semiotics of enthesitis in spondyloarthritis
In spondyloarthropathies, including psoriatic arthritis, sonography may demonstrate peritendionous inflammation as well as inflammatory enthesitis in tendon attachment zones. According to Jacobson (Fundamentals of Musculoskeletal Ultrasound, 2026), characteristic findings include:
- pathological hypoechogenicity of the enthesis zone;
- hyperemia (on power Doppler);
- erosions;
- enthesophytes.
A critical distinction is differentiation between degenerative and inflammatory enthesophytes: correlation with radiography assists in differentiation, as inflammatory enthesophytes are ill-defined, unlike degenerative ones (Jacobson, 2026).
Enthesitis definition by OMERACT
OMERACT (Outcome Measures in Rheumatology) is an international initiative for standardization of outcome measures in rheumatology. The definition of enthesitis in spondyloarthritis on ultrasound was developed within a Delphi process followed by an exercise on image reading reproducibility (Terslev L, Naredo E, Iagnocco A et al. Defining enthesitis in spondyloarthritis by ultrasound: results of a Delphi process and of a reliability reading exercise. Arthritis Care Res (Hoboken) 2014; 66: 741-748, cited in EFSUMB Guidelines Part I, 2022).
Specific elementary findings included in the OMERACT consensus definition for enthesitis in SpA are not textually provided in the given fragments [to be clarified]. According to general ultrasound semiotics (Jacobson, 2026), assessed findings include hypoechogenicity, hyperemia, erosions, and enthesophytes.
MASEI Index
MASEI (Madrid Sonographic Enthesitis Index) is an ultrasound index for quantitative assessment of enthesitis. In the provided source fragments, detailed characteristics of the MASEI index—enumeration of assessed entheses, lesion elements, and scoring thresholds—are absent [to be clarified]. Proper application of the index requires consultation of the original methodology source.
Practical notes on conclusion formulation
When describing enthesitis in the report, it is advisable to document specific morphological findings (hypoechogenicity, Doppler hyperemia, erosions, enthesophytes) with localization. According to Medtrain Consensus materials (2026), semi-quantitative OMERACT gradations (e.g., for osteophytes within OMERACT-OARSI framework) are primarily applied in research contexts and during dynamic monitoring, and in routine clinical reporting in the RF they are not a mandatory standard.
Frequently asked questions
What ultrasound findings characterize enthesitis in spondyloarthritis?
Pathological hypoechogenicity of the attachment zone, hyperemia, erosions and enthesophytes, and possible peritendionous inflammation (Jacobson, 2026).
How to differentiate inflammatory enthesophyte from degenerative?
Correlation with radiography helps: inflammatory enthesophytes are ill-defined, unlike degenerative ones (Jacobson, 2026).
Where is the OMERACT definition of enthesitis established?
In the work by Terslev et al. (Arthritis Care Res, 2014) based on a Delphi process and reading reproducibility exercise (cited in EFSUMB Guidelines Part I, 2022). The complete enumeration of elements is not provided in the given fragments [to be clarified].
What is the MASEI index?
An ultrasound index for quantitative assessment of enthesitis. Detailed parameters (assessed entheses and scores) are absent in the provided fragments [to be clarified].
Should OMERACT gradations be used in routine reporting?
In routine practice in the RF, semi-quantitative OMERACT gradations are not a mandatory standard; they are applied in research and dynamic monitoring (Medtrain Consensus, 2026).