E171 Beyond the numbers: unmasking giant cell arteritis with ultrasound/biopsy despite normal inflammatory markers - a case series

Background/Aims Giant cell arteritis (GCA) is a sight-threatening illness requiring prompt diagnosis and treatment. Giant Cell Arteritis Probability Score (GCAPS) has been proposed as a triage tool with scores ≥10 representing a high probability of disease and <10 representing low probability. Raised inflammatory markers (such as C-reactive protein [CRP] or erythrocyte sedimentation rate [ESR]) are also used frequently to assist in referral. Some patients present with normal inflammatory markers and GCAPS scores which are sub-threshold, presenting a risk for missed diagnosis. We present a case series suggesting patients may present with normal inflammatory markers and low GCAPS scores but have both some biopsy and ultrasound confirmation of GCA, raising concerns that current triage strategies may overlook genuine cases of GCA. Methods We undertook a retrospective analysis of clinical, laboratory, imaging, and histological data from five patients diagnosed with GCA at our institution with CRP ≤10 mg/L and normal ESR ≤20 mm/hr. The GCAPS score, imaging and histological findings were assessed for diagnostic features of GCA (e.g. halo sign or inflammatory infiltrate). Results 5 patients (mean age 82 years, 3 female) with classical signs and symptoms of GCA - new headache, scalp tenderness, or jaw claudication -, had CRP ≤10 mg/L, and three had normal ESR levels. Despite this, every patient had temporal artery USS features displaying the characteristic “halo” sign. Biopsy in four patients was consistent with arteritis. GCAPS stratification showed three patients scored <10 (range 7-9), currently classified as “low probability.” However, all had either an imaging or biopsy result consistent with GCA. The other two patients scored ≥10 (range 10-12) which remains internally consistent with “high probability”, and similarly, all had biopsy/imaging evidence of GCA. This highlights that, while GCAPS is a helpful tool for triage, scores <10 do not safely exclude diagnosis, and should not exclude diagnosis, especially in the context of classical clinical signs and symptoms. Conclusion This case series demonstrates that normal inflammatory markers and GCAPS scores <10 should not rule out the diagnosis of GCA. In fact, if GCAPS and blood tests had been used alone to base decisions, the three patients presented in this series would not have been expedited for investigation, and this could ultimately have resulted in a delay in treatment, risking vision loss. The findings in this case series illustrate the benefit of using GCAPS alongside clinical expertise and vascular imaging, and biopsy rather than strict cut-points. Further studies with higher numbers of participants are needed to assess the sensitivity of the <10 cut-point, especially in cases of seronegative GCA. Larger studies are needed to reassess the sensitivity of the GCAPS <10 threshold and to better characterise seronegative GCA presentations.