Can Colour Doppler Ultrasound Replace Temporal Artery Biopsy for the Diagnosis of GCA?

Patients with Giant Cell Arteritis (GCA) require high-dose corticosteroid treatment for 1-2 years. Many of these patients are elderly with multiple co-morbidities and a high risk of having complications to corticosteroids. It is therefore imperative that the diagnosis of GCA is accurate.

The most commonly used diagnostic test is temporal artery biopsy (TAB). However, given the patchy nature of the disease, there are false negatives and physicians often rely on clinical judgment and classification criteria for diagnosis. Colour doppler ultrasound (CDUS) detects inflammation in the arterial wall, the so-called "halo sign" and may be an alternative to TAB.

Several abstracts reported on the use of CDUS in GCA. Poster #1958 presented a meta-analysis of studies investigating the performance CDUS for diagnosis of GCA. Compared to ACR classification criteria, the sensitivity was 68% and specificity was 93%. Another study (abstract # 1960) showed that inter-observer agreement was very good after an extensive training program.

In a large study from the UK (abstract #2160), 430 patients underwent both TAB and CDUS within 7 days of starting corticosteroids. These patients were followed prospectively and the "gold standard" for diagnosis was the ACR criteria at baseline, confirmed at 6 months follow-up (physicians were blinded to results of diagnostic tests). They found that CDUS had a sensitivity of 54% and a specificity of 80%, whereas TAB had a sensitivity of 34% and a specificity of 100%. Because of the low sensitivity, the investigators proposed the following algorithm:

• If there was a high or moderate clinical suspicion of GCA, the patient would undergo CDUS; if negative they would go on to have a TAB.

• If low suspicion of GCA, then only CDUS would be performed and if negative, then no further testing.

The sensitivity with this approach increased to 95% but specificity was only 77%. This approach would provide cost savings because ultrasound is less expensive than TAB.

CDUS appears to be a promising modality for decreasing the number of false negatives seen with TAB (at least in centres with well-trained personnel and high-end equipment). Given that there are many complications of long-term corticosteroids, the false positive rate with CDUS is concerning. Other strategies using CDUS, TAB and potentially other imaging modalities, may further improve diagnosis of disease and flares of disease.

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