Normal inflammatory markers in giant cell arteritis: a diagnostic blind spot.

Giant cell arteritis (GCA) is a vasculitis requiring urgent diagnosis. Although Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) are important for making the diagnosis, some GCA patients have normal inflammatory markers. We retrospectively analyzed GCA patients with normal versus elevated inflammatory markers to evaluate for differences in clinical presentation and vascular ultrasound to aid in the diagnosis of GCA patients with normal ESR and CRP. We conducted a retrospective study with patients diagnosed with GCA through a Fast Track Clinic (FTC). Clinical presentation and ultrasound results were compared in 23 GCA patients with normal ESR and CRP to 107 GCA patients with elevated ESR and/or CRP. We incorporated an additional 159 patients without GCA to calculate the sensitivity and specificity of ESR and CRP for detecting GCA. Data were analyzed using Pearson Chi-square, Fisher's exact test and ROC curves. CRP is 74% sensitive and 49% specific (AUC = 0.675) compared to ESR with 48% sensitivity and 72% specificity (AUC = 0.644) for detecting GCA. Patients with a longer period between onset of symptoms and measurement of markers (mean of 35 versus 20 days) were more likely to have normal markers (p = 0.03). GCA patients present similarly regardless of inflammatory markers. Patients with normal inflammatory markers had a significantly longer time between symptom onset and inflammatory marker measurement. ESR and CRP have some diagnostic accuracy, low inflammatory markers should not preclude a GCA work-up.