Probability-based algorithm using ultrasound and additional tests for suspected GCA in a fast-track clinic
Alwin Sebastian1, Alessandro Tomelleri1,2, Abdul Kayani1
1Rheumatology, Southend University Hospital NHS Foundation Trust, Westcliff-on-Sea, UK.
Insights
A new algorithm using the Southend pretest probability score (PTPS) effectively triages patients with suspected giant cell arteritis (GCA). This approach improves diagnostic accuracy and streamlines investigations, enhancing the utility of ultrasound (US) in GCA diagnosis.
Area of Science:
- Rheumatology
- Vascular Medicine
- Diagnostic Imaging
Background:
- Giant cell arteritis (GCA) presents with diverse clinical symptoms, necessitating accurate and timely diagnosis to rule out mimics.
- Urgent referrals for suspected GCA require a robust diagnostic process to ensure appropriate management.
- Current diagnostic pathways may lack efficiency in stratifying patients and guiding investigations.
Purpose of the Study:
- To develop an integrated, end-to-end algorithmic process for the rapid confirmation or exclusion of giant cell arteritis (GCA).
- To establish a probability score triage system to guide subsequent investigations, including ultrasound (US).
- To enhance the diagnostic performance of US in suspected GCA cases.
Main Methods:
- Development of a fast-track algorithm stratifying patients into low-risk (LRC), intermediate-risk (IRC), and high-risk (HRC) categories based on the Southend pretest probability score (PTPS).
- Retrospective analysis of case records for patients referred with suspected GCA.
- Assessment of the algorithm's diagnostic performance, particularly the role of US, in a cohort of referrals from 2018-2019.
Main Results:
- The algorithm categorized 354 referrals: LRC (151), IRC (137), and HRC (66), with 89 confirmed GCA cases.
- Ultrasound (US) demonstrated high diagnostic performance: overall sensitivity 97%, specificity 97%, and accuracy 97%.
- In the HRC group, US sensitivity was 94% and specificity 85%; in the IRC group, sensitivity was 100% and specificity 97%; in the LRC group, specificity was 98%.
Conclusions:
- The Southend PTPS algorithm effectively stratifies fast-track referrals for suspected GCA and aids in excluding alternative diagnoses.
- The algorithm enhances the interpretation of US findings within the clinical context, clarifying the diagnostic approach.
- Integration of PTPS with US significantly improves diagnostic test performance and identifies patients requiring further evaluation.
Objectives:
Clinical presentations of giant cell arteritis (GCA) are protean, and it is vital to make a secure diagnosis and exclude mimics for urgent referrals with suspected GCA. The main objective was to develop a joined-up, end-to-end, fast-track confirmatory/exclusionary, algorithmic process based on a probability score triage to drive subsequent investigations with ultrasound (US) and any appropriate additional tests as required.
Methods:
The algorithm was initiated by stratifying patients to low-risk category (LRC), intermediate-risk category (IRC) and high-risk category (HRC). Retrospective data was extracted from case records. The Southend pretest probability score (PTPS) overall showed a median score of 9 and a 75th percentile score of 12. We, therefore, classified LRC as PTPS <9, IRC 9-12 and HRC >12. GCA diagnosis was made by a combination of clinical, US, and laboratory findings. The algorithm was assessed in all referrals seen in 2018-2019 to test the diagnostic performance of US overall and in individual categories.
Results:
Of 354 referrals, 89 had GCA with cases categorised as LRC (151), IRC (137) and HRC (66). 250 had US, whereas 104 did not (score <7, and/or high probability of alternative diagnoses). In HRC, US showed sensitivity 94%, specificity 85%, accuracy 92% and GCA prevalence 80%. In LRC, US showed sensitivity undefined (0/0), specificity 98%, accuracy 98% and GCA prevalence 0%. In IRC, US showed sensitivity 100%, specificity 97%, accuracy 98% and GCA prevalence 26%. In the total population, US showed sensitivity 97%, specificity 97% and accuracy 97%. Prevalence of GCA overall was 25%.
Conclusions:
The Southend PTPS successfully stratifies fast-track clinic referrals and excludes mimics. The algorithm interprets US in context, clarifies a diagnostic approach and identifies uncertainty, need for re-evaluation and alternative tests. Test performance of US is significantly enhanced with PTPS.
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