Value of temporal artery biopsy length in diagnosing giant cell arteritis

Background: Giant cell arteritis (GCA) is considered an ophthalmological emergency with severe sight and life-threatening sequelae. Temporal artery biopsy (TAB) is the current gold standard for the diagnosis of GCA; however, the required length of biopsy remains an issue of contention in the literature. Methods: Retrospective case-control study of a consecutive cohort of 545 patients who had undergone TABs across five hospitals between 1 January 1992 and 1 January 2016. In patients with either positive or negative TABs, we collected age, sex, biopsy length and erythrocyte sedimentation rate (ESR). Results: A total of 538 patients were included in the final analysis. Of these, 23.4% of TABs were positive, with the average length being 17.6mm. There was a significant difference in means for positive (19.9mm) and negative (16.8mm) biopsies (P=0.0009). Each millimetre increase in TAB length increased the odds of a positive TAB by 3.4% (P=0.024). A cut-off point of ≥15mm increased the odds of a positive TAB by 2.25 compared with a TAB <15mm (P=0.003). We also found that ESR≥50mm/h was a very strong predictor for a positive TAB result (P<0.0001). Conclusion: Biopsy length and ESR were significant predictors of a pathological diagnosis of GCA. We also found that the optimal length threshold predictive for GCA was 15mm in order to avoid a false-negative GCA diagnosis. Although TAB remains the gold standard for diagnosis, clinicians should refer to both clinical and pathological data to guide their management.