To the Editor:
We appreciate the comments from Milchert, et al1 on our study evaluating the involvement of femoropopliteal arteries in giant cell arteritis (GCA)2. In their letter, they describe 2 cases with different clinical manifestations of extracranial GCA, including 1 patient with suspected vasculitis of the lower extremities. They discuss the difficulties in discriminating between vasculitis and arteriosclerosis in clinical practice.
Detection of a homogenous, hypoechogenic, circumferential vessel wall thickening by color duplex sonography (CDS) has been shown to be specific for diagnosis of extracranial GCA3. However, we agree with Milchert and colleagues that the accuracy of this method in evaluating the carotid and lower extremity arteries may be hampered in patients exhibiting concomitant, calcified arteriosclerotic lesions4,5,6. It is of interest in this context that, as a result of the high prevalence of arteriosclerosis of lower extremity arteries in the elderly population with GCA, 18F fluorodeoxyglucose-positron emission tomography (FDG-PET) imaging has a low specificity for diagnosis of vasculitis of the lower extremity arteries7. It is our hypothesis that concomitant arteriosclerosis of the lower extremity arteries results in the sonographic “beaded tube” appearance of the innermost layer of the thickened vessel wall in vasculitis of the femoropopliteal arteries (Figure 1)2,6.
A female patient age 70 years with bilateral critical leg ischemia secondary to giant cell arteritis with histological proof after bypass surgery. Color duplex sonography of the superficial femoral artery depicts long-segment, circumferential, hypoechogenic wall thickening with a “beaded tube” appearance of the innermost layer (arrows).
By contrast, arteriosclerosis is very uncommon in the distal subclavian and axillary arteries, and vascular 18F-FDG uptake as well as the hypoechogenic, circumferential wall thickening of these arteries depicted by CDS can be considered to be virtually pathognomonic for GCA in patients aged ≥ 50 years4,7. Of note, vasculitis of the subclavian and/or axillary arteries was detected in 74.2% of our patients with involvement of the femoropopliteal arteries and in all except 1 patient with carotid artery involvement by CDS criteria2,4. Therefore, a sonographic finding consistent with vasculitis of the proximal arm arteries strongly supports a suspected diagnosis of GCA of the lower extremity or carotid arteries. We and others suggest routine examination of the proximal arm arteries in all patients with suspected GCA8. Improvement of ischemic symptoms after initiation of corticosteroid treatment, as reported for GCA of the proximal arm arteries, may further substantiate the vasculitic expression in patients presenting with peripheral arterial disease9.
