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Highlights from

American College of Rheumatology

annual meeting 2018

Chicago, Illinois 19-24 October 2018

Diagnosis of giant-cell arteritis more accurate with PET/CT scan than temporal artery biopsy

Take-home messages
  • PET/CT provides good diagnostic accuracy for giant-cell arteritis compared with temporal artery biopsy
  • High negative predictive value suggests a role for ruling out giant-cell arteritis
  • PET/CT improved identification of alternative diagnoses
“PET/CT is a non-invasive scan that takes around 90 minutes to complete, and until now has not been systematically studied in GCA.”

Dr Anthony Sammel Rheumatologist, Royal North Shore Hospital, St Leonards, Sydney, Australia

Positron emission tomography (PET) combined with computed tomography (CT) in a combined scan of the head, neck and thorax, showed good diagnostic accuracy compared with temporal artery biopsy (TAB) in patients suspected of having giant-cell arteritis (GCA), show results of the first study of its kind. Specifically, the high negative predictive value of 98% indicates that it could be used as a first-line test to rule out GCA.

Presenting the results at the 2018 American College of Rheumatology/ Association of Rheumatology Health Professionals (ACR/ARHP) Annual Meeting was Dr Anthony Sammel, a rheumatologist from the Royal North Shore Hospital, St Leonards, Sydney, Australia. “A PET/CT scan where we include the arteries of the head, neck and chest has very good diagnostic accuracy for GCA. We believe these findings support its use as a first-line test for the disease, and may mean that a significant number of patients may not need to go on to have a TAB,” he said, commenting on the results.

“In the hospital where we conducted the study, the manageable cost of PET/CT means this will now be my first-line test, and if the result is discordant with what I suspect then I’ll do a biopsy,” he added.

GCA, which mainly occurs in patients over 50, is a form of vasculitis that often involves the arteries of the scalp and head, especially the arteries over the temples. Arterial inflammation occurs due to an inappropriate immune response, which can cause artery blockage and vision loss in around 25% of untreated patients and can lead to damage of artery walls and rupture of the aorta. Headache, jaw pain, and stiffness are also possible, according to Dr Sammel.

TAB has been used for diagnosis of GCA for decades. “Biopsy is invasive and uncomfortable for patients and may occasionally be complicated by bleeding, scalp and/or nerve damage,” he noted, explaining the drawbacks of the procedure. “Also, biopsy is associated with false negatives in a proportion of patients due to the small amount of artery sampled during the procedure, and because it is a patchy condition and might involve just the neck or temporal artery, 2/10 patients with the condition can have a negative biopsy,” he added.

Only in the past 5-10 years has newer-generation PET/CT scanning technology been available to detect inflammation in the smaller temporal, occipital, maxillary or vertebral arteries, which are classically involved in GCA, said Dr Sammel. “PET/CT is a non-invasive scan that takes around 90 minutes to complete, and until now has not been systematically studied in GCA,” he explained.

In view of this, the researchers aimed to compare this technology (the PET/CT time-of-flight scanner) with TAB to investigate the accuracy of GCA diagnosis. “We wanted to improve ability to diagnose this condition. It’s difficult to diagnose because its presentation can mimic other conditions, for example infection or cancer.”

Explaining the rationale for the study, Dr Sammel said that, “patients and their doctors increasingly seek non-invasive, timely, accurate and low-risk diagnostic tests. This is especially important for giant-cell arteritis, where symptoms are often non-specific, and a delay in diagnosis can lead to permanent vision loss.”

The study enrolled a total of 64 patients newly suspected of GCA over 20 months. All underwent a combined PET/CT scan from the vertex to diaphragm within 72 hours of starting corticosteroids and before TAB. “It’s important to scan before the corticosteroids because if delayed, the scan can be inappropriately negative,” said Dr Sammel. Of the 64 patients, 58 underwent TAB.

Clinicians were blinded to clinical and biopsy data and they independently reported scans as globally positive or negative for GCA. They also rated the grade at which the tracer (fluorodeoxyglucose, or FDG) uptake exceeded the background blood pool for 18 artery segments and the maximum grade per patient (0=none, 1=minimal/ equivocal, 2=moderate and 3=very marked). The clinical diagnosis was made at the 6-month mark by consensus between the PET/CT blinded treating clinician and blinded external reviewers.

Of those that had TAB, 12 (21%) were positive and 11 of these (92%) had a positive PET/CT scan. In those that had negative TABs (46 patients), 39 (85%) also had a negative PET/CT scan. “So, we take from this that PET/CT had very good diagnostic accuracy for giant-cell arteritis,” Dr Sammel remarked.

Of note, two out of seven ‘false positive’ cases on PET/CT had disease flares consistent with GCA when corticosteroids were weaned, suggesting that PET/CT may have diagnosed the condition more accurately than biopsy.

“We managed to find some other useful information from the scans that might not have been visible from ultrasound or other diagnostic modalities. Firstly, we found alternative diagnoses in one in five patients: seven had acute infection identified on scan and one had a very serious neck infection mimicking GCA and, had he been treated with corticosteroids for 2 weeks until the biopsy was returned, he could have had a very poor outcome,” he pointed out. “We also identified five cancers and one case of thyroid disease. Five of the 12 patients who had a positive TAB were found to have inflammation of the aorta, which is important because these people might develop aortic rupture in the longer term.”

Commenting on the clinical significance of the findings, Dr Sammel remarked that, “There is a learning curve to confidently assess FDG tracer uptake in the smaller superficial cranial and vertebral arteries. With this in mind, we would advocate its introduction into clinical care with a low threshold to undertake temporal or other confirmatory imaging tests when the PET/CT scan is equivocal or discordant with the clinical suspicion of GCA. The study indicates that a negative scan may be particularly useful in ruling out the disease in patients who have a low pre-test probability of GCA.”

Based on Sammel A, Hsiao E et al. The diagnostic accuracy of PET/CT scan of the head, neck and thorax compared with temporal artery biopsy in patients newly suspected of having GCA (abstract L15). Presented on Tuesday October 23 2018.

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