What is the emergent imaging for giant cell arteritis (GCA)?

From the Guidelines

Emergent imaging for temporal arteritis should involve high-resolution color Doppler ultrasound of the temporal arteries as the first-line imaging modality, as recommended by the most recent guidelines 1. This non-invasive technique can quickly visualize the characteristic "halo sign" (vessel wall edema) and stenosis or occlusion of the temporal arteries. Some key points to consider when using ultrasound for temporal arteritis diagnosis include:

• The "halo sign" is the ultrasound finding most suggestive of GCA, as noted in the EULAR recommendations 1.
• Ultrasound should be performed by a trained specialist using appropriate equipment and settings, as emphasized in the EULAR guidelines 1. If ultrasound is unavailable or results are inconclusive, MRI with gadolinium enhancement of the cranial vessels should be performed, focusing on the temporal and other cranial arteries to detect wall thickening and enhancement, as suggested by the 2023 update of the EULAR recommendations 1. CT angiography represents another alternative when MRI is contraindicated. However, imaging should never delay treatment with high-dose corticosteroids (typically prednisone 60mg daily or equivalent) if temporal arteritis is strongly suspected clinically, as vision loss can occur rapidly and may be permanent, as highlighted in the guidelines 1. Imaging serves as an adjunct to clinical evaluation and laboratory tests (particularly erythrocyte sedimentation rate and C-reactive protein), with temporal artery biopsy remaining the gold standard for definitive diagnosis. The urgency for imaging stems from the need to prevent ischemic complications, especially irreversible blindness, which occurs in up to 20% of untreated patients. It is essential to note that the choice of imaging modality may depend on availability and expertise, as well as the specific clinical presentation of the patient, as discussed in the ACR appropriateness criteria 1. In general, the most recent and highest quality study, in this case, the 2023 update of the EULAR recommendations 1, should guide the choice of emergent imaging for temporal arteritis.

From the Research

Emergent Imaging for Temporal Arteritis

The emergent imaging for temporal arteritis, also known as giant cell arteritis (GCA), includes various modalities that help in diagnosing and evaluating the condition. Some of the key imaging techniques used are:

• Magnetic Resonance Imaging (MRI): High-resolution MRI can reveal mural inflammatory changes of the superficial temporal artery in GCA 2. It has a sensitivity of 93.6% and a specificity of 77.9% in diagnosing GCA 3.
• Duplex Ultrasound: Color-coded duplex sonography (CCDS) has a sensitivity of 67% and a specificity of 91% in diagnosing GCA 4. It is also a viable option for evaluating GCA, especially as a first-line diagnostic tool 5.
• Positron Emission Tomography-Computed Tomography (PET-CT) scan: 18F-Fluorodeoxyglucose (FDG)-PET shows increased FDG uptake of inflamed artery walls, delineating increased metabolic activity 6.
• Computed Tomography (CT): CT may reveal a homogeneous, concentric thickening of the arterial wall, as well as aneurysms and stenoses 6.

Comparison of Imaging Modalities

The diagnostic performance of different imaging modalities in GCA has been compared in various studies. For example:

• A study found that high-resolution MRI and CCDS had comparable diagnostic power in detecting GCA, with sensitivities of 69% and 67%, respectively, and specificities of 91% and 91%, respectively 4.
• Another study found that MRI had a higher sensitivity (93.6%) and negative predictive value (98.2%) compared to temporal artery biopsy, suggesting that MRI could be used as the initial diagnostic procedure in GCA 3.

Clinical Applications

The choice of imaging modality may depend on the clinical setting and the patient's presentation. For example:

• In patients with a high suspicion of GCA who present with visual disturbances, initiation of high-dose intravenous corticosteroids should not be delayed by imaging 6.
• Ultrasound, FDG-PET, and MRI are the recommended imaging techniques in GCA, and may be used to confirm extracranial large vessel vasculitis 6.