A new prediction tool for giant cell arteritis (GCA) combines ultrasonography and clinical assessment to further improve disease detection.

The tool, which incorporates a halo count and the Southend Giant Cell Arteritis Probability Score (HAS-GCA score) based on demographics, symptoms, physical signs, and blood CRP, “reliably confirms” GCA and separates the condition from GCA mimics, according to its UK developers.

Using data from 229 patients with suspected new-onset GCA who were referred to fast-track clinics, the team led by rheumatologist Dr Alwin Sebastian found that adding the halo count – i.e. the total number of halo signs at eight sites in the bilateral temporal and axillary arteries – improved the accuracy of the prediction model, as shown by an increase in the area under the curve to 0.969 from 0.918 with SGCAPS alone.

Using the combined HAS-GCA score enabled 74% of patients to be classified as having either a low or high probability of giant cell arteritis, with misclassification observed in just 2% of the low and 3% of the high probability groups.

In the low probability group, misclassification occurred in patients with isolated vertebral arteritis, while misclassified patients in the high probability group were diagnosed with cancer mimicking GCA.

Interestingly, all misclassified patients in the low probability group were women, while all those misclassified in the high probability group were men.

“This was associated with the perceived absence of halo signs in the respective women and high halo counts in the men,” wrote the authors in their paper published in The Lancet Rheumatology (link here).

“Previous studies have already indicated that men might have more pronounced findings on ultrasonography than women, probably because of differences in arterial calibre and wall thickness. Future studies should address whether IMT dimensions can be corrected for age and sex,” they noted.

Overall, the new point-of-care prediction tool “should improve the accuracy of giant cell arteritis diagnosis in clinical practice by encouraging interpretation of ultrasonographic findings in the light of previous standardised clinical probability scoring,” the authors said.

However, they also recommended additional testing for patients where there is “disease uncertainty, discordance between clinical assessment and ultrasound imaging, unexplained systemic symptoms and inflammation, and poor response to treatment”.

It was also highlighted that “expertise in vascular ultrasonography is not yet available everywhere”, but the researchers expressed hope that the study’s findings would “encourage the use of SGCAPS and help in disseminating interest and skill in the application of vascular ultrasonography in clinics and populations that currently do not have this facility”.

The study had key limitations, including that the HAS-GCA score itself had not been validated, and that diagnostic uncertainty can persist for longer than the 6-month post diagnosis follow-up timepoint used in the study.

The HAS-GCA score “should be considered as an adjunct to clinical reasoning of clinicians; improving the safety of giant cell arteritis diagnosis, when applied correctly in clinical practice”, the authors concluded, but also cautioned that the model still needs “further prospective validation through international networks in multicentre independent datasets”.

In a linked editorial (link here), US rheumatologists Dr Zandra Walton and Dr Naomi Patel, Massachusetts General Hospital, Boston, noted that efforts to increase the accuracy of GCA diagnoses “are valuable given the risks of both underrating and overrating” the condition.

“The ability of non-invasive diagnostic algorithms to identify patients at the highest and lowest risk, in whom to appropriately administer or withhold therapy, has great value”, they said.

“However, patients who remain in this indeterminate category pose ongoing challenges”, they added.

“Future studies will hopefully identify and optimise diagnostic imaging modalities as well as other novel non-invasive, low-cost biomarkers of giant cell arteritis to help clinicians navigate these high-stake uncertainties”.