Background: Giant cell arteritis (GCA) is a systemic inflammatory disease primarily affecting an elderly population. Ocular ischemia is a serious complication, and rapid and reliable diagnosis is therefore important. High frequency ultrasound (US) and superb microvascular imaging (SMI) may provide more information regarding activity of the disease. SMI is a low- flow Doppler technology with high resolution and high framerate allowing detection of neovascularization. The aim of this study was to evaluate if US with SMI, in combination with a novel developed GCA grading scale, based on US vessel wall appearance and compression test, may be used to differ between active or stable disease, and provide a hint of the global burden of inflammation. Methods: Fifty consecutive patients, 32 women and 18 men, mean age 74 years, with GCA suspicion, were investigated. Intima-media thickness (IMT) and vessel wall appearance was evaluated with high frequency US (Canon Aplioi800) in carotid and central arteries (linear transducer i11LX3) as well as in temporal arteries (hockeystick transducer i22LH8). SMI was used in the evaluation of neovascularization. Compression test was done at multiple locations of the temporal arteries. A theoretical model was created to characterize inflammatory vessel wall changes in temporal arteries (Table 1). Grade I – Increased IMT, low-medium echogenicity with neovascularization and/or oedema extending into the media, and/or signs of inflammation outside the vessel walls, and positive compression test (highly active inflammation). Grade II – As Grade I but without neovascularization and/or oedema and/or signs of inflammation outside the vessel walls (active inflammation). Grade III – Increased IMT, increased echogenicity, and positive compression test (longstanding arteritis). Widespread disease – Grade I, II or III with addition of inflammatory findings in facial, carotid and/or central arteries. Results: Inflammatory changes were found in the temporal arteries in eighteen patients (36%), five (28%) of these patients also showed abnormalities in facial, carotid or central arteries. One patient demonstrated inflammatory changes restricted to carotid and central arteries. Active arteritis, with increased IMT, and low-medium echogenicity of the increased vessel wall was found in fifteen cases. Neovascularization was detected with SMI in four patients; oedema extending into the media was visualized in one patient, and signs of inflammation outside the vessel walls in six cases. High echogenic vessel walls with increased IMT, indicating long-standing arteritis were found in three patients. Seven patients were judged as Grade I, eight patients grade II, and three patients grade III. IMT in the common temporal artery differed significantly between patients with and without positive ultrasound signs, 0.61±0.21 mm vs. 0.22±0.06 mm (p<0.001). Conclusion: High frequency US with SMI seems to be a promising tool to detect and monitor inflammatory changes and differ between longstanding or newly developed/active GCA. The novel GCA grading system may aid in judging inflammatory activity and evaluate the global inflammatory burden. Further studies regarding the relation between vessel wall appearance, laboratory findings and clinical disease activity are warranted. Disclosures: None. Figure 1. Grading scale and US characteristics, IMT; Intima Media Thickness, US; Ultrasound .