https://orcid.org/0000-0002-0173-0668
Dear Editor, In patients with suspected GCA, ultrasound of the temporal and axillary arteries is recommended as the first imaging modality [1]. Fast-track clinics have been established in many countries in order to facilitate early diagnosis of GCA and to prevent irreversible sight loss. Point-of-care ultrasound (POCUS), referring to ultrasonography performed at bedside in real-time, is advancing in the field of rheumatology. An innovative, inexpensive (<US$2000), chip-based. handheld ultrasound probe (Butterfly iQ+, Butterfly Network, Guilford, CT, USA) was recently developed, where the probe is connected wirelessly to an iPhone/iPad instead of being attached to a traditional stand US machine. It enables high-resolution US images, with a single probe replacing the many piezoelectric probes on a traditional US machine by enabling multiple frequencies from 1 to 10 MHz as well as many different organ presets. The application of the Butterfly iQ at the point of care in a fast-track GCA clinic offers the possibility to examine patients immediately and almost everywhere without shifting a standard US machine or the patient from one room to another. However, the reliability of the Butterfly iQ for examining temporal and axillary arteries in GCA patients has not yet been tested against a standard US machine.
We prospectively recruited 10 newly diagnosed treatment-naïve GCA patients in whom diagnosis was made by a board-certified rheumatologist. All of the patients also fulfilled the expanded ACR classification criteria [2]. Clinical, demographic, US and laboratory data were collected. The ethics committee of the University Hospital of Bonn approved the study (Lfd.Nr. 097/18). Each patient underwent two consecutive US examinations of bilateral temporal (common, parietal and frontal branches), facial, carotid and axillary arteries in accordance with the OMERACT protocol for GCA by two blinded sonographers with long experience in US diagnosis of GCA (V.S.S. and P.K.) [3]. For the first examination, the Butterfly iQ device (manufactured in 2020) was used, while the second exam was conducted using a Logiq S8 (manufactured in 2018; GE Healthcare, Chicago, IL, USA) with an 18 MHz and a 6–15 MHz probe. Each artery was examined for the ‘halo sign’; temporal arteries were also assessed for the compression sign [3]. Furthermore, the intima-media thickness of each segment was measured according to a previously published protocol [4]. Cohen’s κ agreement was calculated for each artery.
Four patients (40%) were female. The patients’ mean age was 76.1 years (s.d. 9.7), mean BMI was 26.9 kg/m2 (s.d. 5.61) and mean CRP level was 65.5 mg/l (s.d. 46.5).
Eight patients (80%) presented with new temporal headache and visual symptoms, six (60%) reported jaw claudication, five (50%) suffered from jaw pain and two (20%) had burning of the tongue. Fever and weight loss were reported by three patients (30%) and one had PMR.
Fig. 1 shows the results of the US examinations. In comparison to the GE Logiq S8 (gold standard), the Butterfly iQ probe demonstrated a sensitivity and specificity of 80.8% and 87.0%, respectively, considering previously published IMT cut-offs for GCA [4, 5]. The halo sign had a sensitivity and specificity of 100% and 95.3%, respectively, while the compression sign had a sensitivity and specificity of 100% and 94.5%, respectively, compared with the gold standard US machine.
Comparison of US findings between the Butterfly iQ and the GE Logiq S8
Intima-media-thickness cut-off values for the common temporal artery, the frontal and parietal branch, the facial artery and the axillary artery were derived from Schäfer et al. [4], while the cut-off values for the common carotid artery were derived from Hocevar et al. [5]. Cohen’s κ agreement was calculated for each artery.
Equal classifications considering established IMT cut-off values were observed in 99 arteries (83.2%), 109 arteries (97.3%) had a positive halo sign and 76 arteries (96.20%) had a positive compression sign.
The mean Cohen’s κ values for the cut-off value decisions, the compression sign and the halo sign were 0.64, 0.9 and 0.93, respectively. Supplementary Fig. S1, available at Rheumatology online, shows US images of the temporal and axillary arteries obtained by the two US systems.
In summary, the novel chip-based handheld US probe Butterfly iQ yielded reliable results for the assessment of temporal and axillary arteries in the diagnosis of GCA patients. Future studies are necessary to assess its validity in a larger cohort.
The Butterfly iQ probe seems to be appropriate for ultrasound diagnosis of suspected GCA.
Funding: No specific funding was received from any funding bodies in the public, commercial or not-for-profit sectors to carry out the work described in this article.
Disclosure statement: The authors declare no conflicts of interest.
Data availability statement
The authors confirm that all data from this study are available within the article.
Supplementary data
Supplementary data are available at Rheumatology online.
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