Summary

Giant cell arteritis (GCA) requires urgent diagnosis and treatment because of the potential for vision loss. This manuscript describes a predictive tool (called the HAS-GCA score) to assess the post-test probability of GCA. This score consists of a two-step approach: (1) calculation of the clinical Southend Giant Cell Arteritis Probability Score (SGCAPS), followed by (2) quantitative ultrasonography. The SGCAPS determines a pre-test probability of low, intermediate or high risk.

A total of 229 patients (84/229 with a final clinical diagnosis of GCA at 6 months) were enrolled in this prospective, multicentre, fast-track study (seven centres in Italy, the Netherlands, Spain and the UK). SGCAPS and quantitative ultrasonography of the temporal and axillary arteries with three scores (i.e., halo count, halo score, and OMERACT GCA Score [OGUS]) were performed at diagnosis.

SGCAPS and all three ultrasound scores discriminated well between patients with and without GCA. A reliability exercise showed that inter-rater and intra-rater reliability was high for all three ultrasound scores. The prediction model combining SGCAPS with halo count, termed the HAS-GCA score, was the most accurate model. The HAS-GCA score was able to classify 169 (74%) of 229 patients into either the low or high probability group, with misclassification observed in two (2%) of 105 patients in the low probability group (both patients with isolated vertebral arteritis) and two (3%) of 64 patients in the high probability group (both eventually diagnosed with cancer mimicking GCA).  

Limitations include the circularity of decision making in the diagnosis of GCA. The HAS-GCA score requires further prospective validation by international networks in independent multicentre datasets.

Impact on Patient Treatment and Future Perspectives

This study addresses a topic of great relevance in the diagnosis of GCA: the need for improved diagnostic approaches. In the interpretation of diagnostic tests in patients with suspected GCA, consideration should be given to the pre-test probability. In patients with a high clinical pre-test probability and a negative initial diagnostic test, a second diagnostic test should be considered.

References:

[1] Sebastian, A., van der Geest, K. S. M., Tomelleri, A., Macchioni, P., Klinowski, G., Salvarani, C., Prieto-Peña, D., Conticini, E., Khurshid, M., Dagna, L., Brouwer, E., & Dasgupta, B. (2024). Development of a diagnostic prediction model for giant cell arteritis by sequential application of Southend Giant Cell Arteritis Probability Score and ultrasonography: a prospective multicentre study. The Lancet. Rheumatology, 6(5), e291–e299. https://doi.org/10.1016/S2665-9913(24)00027-4

Composed by

PD Dr. med. Lisa Christ
Oberärztin

Universitätsklinik für Rheumatologie und Immunologie
Inselspital, Universitätsspital Bern