Compression ratio: a novel method to quantify compressibility as a diagnostic measurement in giant cell arteritis

Objectives: Ultrasonographic assessment of giant cell arteritis (GCA) relies on the demonstration of a non-compressible halo. Several ultrasonographic methods have been developed to quantify arterial wall thickness, however arterial compressibility has not been quantified. This study presents a possible solution for quantifying compressibility to assist in diagnosing GCA.

Methods: Cross-sectional areas of uncompressed and compressed arteries were measured ultrasonographically, and their ratio was calculated (compression ratio (CR)). The values obtained were tested for a relationship with the diagnosis of GCA and diagnostic performance was compared against halo count (HC).

Results: Ultrasound findings from 304 patients (65.8% females) were divided into GCA arm (n = 72) and Not-GCA arm (n = 232). The CR values for patients in the GCA arm were significantly lower than the Not-GCA arm whether compared as the individual patient mean or lowest CR value (Mann-Whitney U test p< 0.001). The CR values observed in this study from a single skilled clinician, suggest a threshold CR value of ≤ 2.3 for predicting a diagnosis of GCA. If confirmed in other studies this would effectively provide a quantitative measure that might help training sonographers confirm a visually identified halo sign and enhance objectivity in ultrasonographic assessment of GCA.

Conclusion: Compression ratio (CR) is a novel quantifiable measure that contributes to the ultrasound assessment of GCA. It is worthy of further research and in clinical application, it is a measurement that may enhance diagnostic certainty.