E1910. Imaging Workup of Giant Cell Arteritis: A Multimodality Approach
  1. Lei Wu; University of Washington
  2. Ethan Bent; University of Washington
  3. Alison Bays; University of Washington
  4. Chengcheng Zhu; University of Washington
  5. Mahmud Mossa-Basha; University of Washington
Giant cell arteritis (GCA) is a large vessel vasculitis in which early diagnosis is critical for preservation of vision. However, the diagnosis can be difficult without invasive temporal artery biopsy (TAB) because patient symptoms are often nonspecific and overlap with many other conditions (1, 2). Clinical criteria set by the American College of Rheumatology to help with diagnosis have low sensitivity and specificity(3). Furthermore, TAB can be falsely negative with poor sensitivity as low as 10%, particularly in those with non-cranial GCA (4, 5). Imaging can be useful and complementary to clinical diagnosis. Imaging modalities which have been shown to be helpful include ultrasound (US), magnetic resonance imaging (MRI) particularly vessel wall MRI (VWI), and F-18 Fluorodeoxyglucose Positron Emission Tomography (PET) with varying diagnostic criteria and diagnostic yield (6-13). We aim to discuss a multimodality approach to the imaging workup and management of patients suspected of having giant cell arteritis.

Educational Goals / Teaching Points
1. Clinical presentation and diagnostic challenges of GCA 2. Indications for imaging for diagnosis and management of complications 3. Diagnostic criteria and diagnostic yield for US, VWI, and PET 4. Technical considerations and contraindications of each modality 5. Current knowledge gap and future directions

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
The sensitivity of US for GCA ranges from 54% to 91.6% and the specificity range from 90% to 100% (14). Imaging features on US include increased arterial wall thickness, luminal stenosis or occlusion and non-compressibility. Vessel wall thickness of 0.42 mm, 0.34 mm, and 0.29 mm have been proposed as cut-off values for common superficial temporal artery (STA), frontal branch of STA, and parietal branch of STA, respectively(14, 15). The advantage of US is its low cost and it is widely available, but the diagnostic performance of US is more operator dependent. The sensitivity of VWI ranges from 69% to 80.6% with specificity of 91% to 97% (8, 16). VWI features of GCA are increased arterial wall thickness and enhancement. A 4-point scale grading system has been proposed. Grade 0 is defined as wall thickness < 0.5 mm without enhancement; grade 1 is wall thickness < 0.5 mm with only slight contrast enhancement; grade 2 is wall thickness > 0.6 mm with prominent enhancement; and grade 3 is wall thickness > 0.7 mm with strong enhancement. Grades 2 and 3 are considered positive (8). The sensitivity and specificity of PET are 83% to 90% and 90% to 98%, respectively (9, 12, 13). PET is considered positive if the arterial wall FDG uptake is greater or equal to that of the liver (13). Both VWI and PET offer the potential advantage of being able to assess the disease activity in patients receiving corticosteroid treatment by evaluating the degree of wall enhancement and FDG uptake respectively.

Imaging is helpful in diagnosis of GCA due to nonspecific symptoms and low sensitivity of TAB. VWI and PET may offer the additional benefit of evaluation of disease activity in patients receiving treatment.