Background/Purpose: Giant cell arteritis (GCA) is the most common large vessel vasculitis, and may be associated with irreversible blindness(1). It is therefore essential to make an early and secure diagnosis. However, GCA often presents a diagnostic challenge; whilst biopsy has been considered the gold standard, in recent years, imaging (ultrasound, MR angiography, CT angiography and PET) has also been validated in GCA. Pre-test probability of disease remains a critical component of GCA assessment and clinical decision making. Recently, the Southend pre-test probability score (PTPS) has been developed to aid GCA assessment (2,3).

We aimed to retrospectively apply the PTPS to patients seen through our GCA Fast Track Clinic (FTC) to assess the utility of this score.

Methods: Patients presenting to the Royal Perth Hospital GCA FTC were consented for prospective data collection. A clinical diagnosis of GCA was based on history, examination, temporal artery ultrasound, and temporal artery biopsy or additional imaging in select cases. We retrospectively calculated the PTPS from data collected between November 2019 and May 2021. We risk stratified patients into low-risk (PTPS < 9), intermediate risk (PTPS 9-12), and high risk (PTPS > 12) groups, and correlated these with the final clinical diagnosis. We then dichotomised the PTPS into (1) low risk or (2) intermediate/high risk groups, to determine the sensitivity, specificity, positive predictive value and negative predictive value.

Results: Of 104 patients, 25 (24%) received the clinical diagnosis of GCA. Using the PTPS, 45 (43%) of the 104 patients were classified low risk, 34 (32%) intermediate and 25 (24%) high risk for GCA. In the low risk category, GCA prevalence was 0%, in the intermediate group GCA prevalence was 15%, and in the high risk category the prevalence was 80% (p< 0.001).

The Southend PTPS (dichotomised) had a sensitivity of 100%, Specificity 56.9%, positive predictive value of 42.3% and negative predictive value of 100%.

Conclusion: The PTPS (applied retrospectively) successfully stratifies patients referred to our fast track clinic into high and low risk for GCA, when using the clinical diagnosis as the gold standard. This tool may have a role in screening referrals to the GCA FTC; the negative predictive value suggests this tool is valuable to exclude GCA.

Reference:

1. Ponte C, Martins-Martinho J, Luqmani RA. Diagnosis of giant cell arteritis. Rheumatology. 2020;59(Supplement_3):iii5-iii16.

2. Laskou F, Coath F, Mackie SL, Banerjee S, Aung T, Dasgupta B. A probability score to aid the diagnosis of suspected giant cell arteritis. Clin Exp Rheumatol. 2019;37(Suppl 117):104-8.

3. Sebastian A, Tomelleri A, Kayani A, Prieto-Penna D, Ranasinghe C, Dasgupta B. Probability based algorythm using US and additional tests for suspected GCA in a fast track clinic. RMD Open 2020. Sep 6(3) e 001297.

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