Systematic review of the literature and a case report informing biopsy-proven giant cell arteritis (GCA) with normal C-reactive protein.

Giant cell arteritis (GCA) is a vasculitis of large- vessels. A markedly elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels are characteristics of GCA, although temporal artery biopsy remains the gold standard for the diagnosis. We describe a case of biopsy-proven GCA showing a heavy infiltration of CD68 macrophages and CD3 T cells and with normal ESR and CRP levels at diagnosis. Key points (1) GCA may occur with normal ESR in a percentage of about 4 to 15 % (although the American College of Rheumatology classification criteria for giant cell arteritis include an ESR of 50 mm/h or more), while it can occur with normal ESR and normal CRP in a percentage of about 0.8 %. So, the clinical suspicion must be confirmed with a positive biopsy. (2) GCA patients with ESR >40 mm/h are characterized by higher incidence of headache and jaw claudication compared to patients with normal ESR. In our case, it occurred with normal ESR. (3) Color duplex ultrasonography is a noninvasive, easy, and inexpensive method for supporting a diagnosis of TA, with a high sensitivity and specificity. It can predict which patient will need TAB.