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We are grateful for the interest in our article and agree with Milchert et al 1 that the slope sign deserves a precise definition. Intimal medial thickness (IMT) of the axillary artery is the current way of assessing large vessel giant cell arteritis (LV-GCA) by ultrasound (US), with a cut-off value of greater than 1.0 mm suggesting LV-GCA.2 Other causes of arterial wall thickening can mimic vasculitis such as atherosclerosis and it is often challenging to differentiate between atherosclerosis and vasculitis related thickening of the axillary artery.3 ‘Slope sign’ is a visual definition of a smooth, homogenous, gradual transition from an abnormal axillary arterial segment with increased IMT to an arterial segment with normal IMT. This should help differentiate between vasculitic and atherosclerotic wall thickening.4 We suggest that sonographers should seek to demonstrate the slope sign in all cases of suspected LV-GCA through the use of panoramic views, if necessary, of the axillary artery from the humeral neck to the origin of the circumflex branch.
We agree with Milchert et al 1 that, in LV-GCA the slope is usually long. However, we disagree that atherosclerosis can demonstrate a sharp or short slope. Our observations are that abrupt, atherosclerotic thickening involves a focal area of arterial wall and therefore cannot be mistaken for a slope. We also have observed that the echotexture of the vasculitic IMT is hypoechoic which transitions smoothly to a normal echo-texture. The retrospective analysis by Milchert et al 5 validates our finding. However, we do not think the axillary-brachial IMT ratio is a surrogate for the slope sign since it does not assess the gradual transition which is a critical part of the definition.
We agree that this sign requires validation and assessment as a marker of disease extent in prospective studies. Our ongoing multicentre HAS GCA study (National Institute for Health Research number 264294), exploring quantitative US halo score as a prognostic and monitoring tool in GCA, has the assessment of slope sign as one of its objectives.
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Handling editor Josef S Smolen
Competing interests None declared.
Provenance and peer review Commissioned; internally peer reviewed.
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