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PET/CT ACCURATELY DIAGNOSES GIANT CELL ARTERITIS COMPARED TO TEMPORAL ARTERY BIOPSY
Newswise — CHICAGO – A combined scan of positron emission tomography (PET) and computed tomography (CT) has good diagnostic accuracy compared with temporal artery biopsy in patients newly suspected of having giant cell arteritis, according to new research findings presented this week at the 2018 ACR/ARHP Annual Meeting (Abstract #L15).
Giant cell arteritis (GCA) is a type of vasculitis, which is a disease involving blood vessel inflammation. In GCA, the vessels most often involved are the arteries of the scalp and head, especially the arteries over the temples, which is why another term for GCA is “temporal arteritis.” PET/CT often is used for imaging of the aorta and primary arterial branches, but newer-generation scanning technology can also detect inflammation in the smaller temporal, occipital, maxillary or vertebral arteries. To explore this further, researchers in Australia conducted a new study to assess the accuracy of a PET/CT time-of-flight scanner compared to temporal artery biopsy (TAB) for the diagnosis of giant cell arteritis in suspected patients.
“Patients and their doctors increasingly seek non-invasive, timely, accurate and low-risk diagnostic tests. This is especially important for GCA, where symptoms are often non-specific, and a delay in diagnosis can lead to permanent vision loss,” said Anthony M. Sammel, MBBS, a rheumatologist at Royal North Shore Hospital in Sydney, and the study’s lead author. “While temporal artery biopsy is well-established for GCA, it can give a falsely negative result in a proportion of patients due to the small amount of artery that is sampled. Furthermore, biopsy is invasive and uncomfortable for patients and may occasionally be complicated by bleeding, scalp and/or nerve damage. PET/CT is a non-invasive scan that takes around 90 minutes to complete.”
The study included 64 newly suspected GCA patients who were enrolled over a 20-month period. All patients underwent PET/CT from the vertex to diaphragm within 72 hours of starting corticosteroid therapy and before TAB. Two nuclear medicine physicians experienced with using PET were blinded to clinical and biopsy data. They independently reported scans as globally positive or negative for GCA. They also rated the grade that the tracer (fluorodeoxyglucose, or FDG) uptake exceeded the background blood pool for 18 artery segments and the maximum grade per patient. Grades were 0=none, 1=minimal/equivocal, 2=moderate and 3=very marked. Discordant results were resolved by consensus among the graders. Clinical diagnosis of GCA was made by consensus at the six-month mark between the PET/CT-blinded treating physician and blinded external reviewers.
Out of the 64 patients, 58 (91 percent) underwent TAB, and 12 of these 58 (21 percent) had biopsies that were positive for GCA. In addition, 21 of the 64 patients (33 percent) had a clinical diagnosis of GCA and 42 (66 percent) met the 1990 ACR criteria for GCA. Compared with TAB, global GCA assessment by PET/CT had a sensitivity of 92 percent, a specificity of 85 percent, a positive predictive value of 61 percent, and a negative predictive value of 98 percent. Interobserver reliability was good, with Cohens kappa =0.65.
Two out of seven PET/CT false-positive cases had GCA-consistent disease flares when their corticosteroids were weaned suggesting that PET/CT may have diagnosed the condition more accurately than biopsy. Defining an uptake grade cut-off of 1+ in any vessel as a positive scan gave the modality a sensitivity of 100 percent and a specificity of 46 percent against TAB, while a cut-off of 2+ gave it a sensitivity of 83 percent and specificity of 83 percent. Four (33 percent) TAB-positive patients had grade 2+ uptake localized to the temporal, occipital, maxillary or vertebral arteries, and this may have been missed on older-generation scans.
In summary, the study’s findings show that the PET/CT protocol has good diagnostic accuracy in patients suspected of having GCA. The high negative predictive value of 98 percent indicates that this protocol could be used as a first-line test to rule out GCA in suspected patients.
“Rheumatologists could consider using this PET/CT scan protocol to help confirm or refute the diagnosis of acute GCA,” said Dr. Sammel. “In attempting to extrapolate the results to clinical practice, it is important to recognize that the study had a modest sample size of 64 patients. 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 TAB 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.”
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About the American College of Rheumatology
The American College of Rheumatology is an international medical society representing over 9,400 rheumatologists and rheumatology health professionals with a mission to empower rheumatology professionals to excel in their specialty. In doing so, the ACR offers education, research, advocacy and practice management support to help its members continue their innovative work and provide quality patient care. Rheumatologists are experts in the diagnosis, management and treatment of more than 100 different types of arthritis and rheumatic diseases. For more information, visit www.rheumatology.org.
Abstract #: L15
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.
Anthony Sammel1, Edward Hsiao2, Geoffrey Schembri2, Katherine Nguyen1, Janice Brewer1, Leslie Schrieber3, Beatrice Janssen1, Peter Youssef4, Clare Fraser5, Elizabeth Bailey6, Dale Bailey6, Paul Roach6 and Rodger Laurent1, 1Royal North Shore Hospital, St Leonards, Sydney, Australia, 2Royal North Shore Hospital, St Leonards, Australia, 3University of Sydney, Sydney, Australia, 4Royal Prince Alfred Hospital, Camperdown, Sydney, Australia, 5Save Sight Institute, Sydney, Australia, 6Royal North Shore Hospital, Sydney, Australia.
Background/Purpose: The diagnostic accuracy of PET/CT against temporal artery biopsy (TAB) in patients suspected of having GCA has not been well studied. PET/CT has traditionally been used to image the aorta and primary branches, but newer generation scanners can also detect inflammation in the smaller temporal (TA), occipital (OA), maxillary (MA) and vertebral arteries (VA). We assessed the accuracy of a newer generation PET/CT time-of-flight scanner for GCA.
Methods: 64 newly suspected GCA patients were enrolled over 20 months. All underwent PET/CT from the vertex to diaphragm within 72 hours of starting corticosteroids and before TAB. Two PET experienced nuclear medicine physicians blinded to clinical and biopsy data independently reported scans as globally positive or negative for GCA. They also rated the grade that tracer (FDG) uptake exceeded background blood pool for 18 artery segments and the maximum grade per patient (0 = none, 1 = minimal/equivocal, 2 = moderate, 3 = very marked). Discordant results were resolved by consensus. The clinical diagnosis was made at the six-month mark by consensus between the PET/CT blinded treating clinician and blinded external reviewers.
Results: 58/64 (91%) patients underwent TAB and 12/58 (21%) biopsies were positive for GCA. 21/64 (33%) had a clinical diagnosis of GCA and 42 (66%) met the 1990 ACR criteria for GCA. Compared with TAB, global GCA assessment by PET/CT had sensitivity (Sn) 92%, specificity (Sp) 85%, positive predictive value (PPV) 61% and negative predictive value (NPV) 98%. Interobserver reliability was good (k = 0.65). Compared with clinical diagnosis, PET/CT had Sn 71% and Sp 91%. 2/7 PET/CT ‘false positive’ cases had GCA consistent disease flares when corticosteroids were weaned. Defining an uptake grade cut-off 1+ in any vessel as a positive scan gave Sn 100% and Sp 46% against TAB while a cut-off 2+ gave Sn 83% and Sp 83%. Four (33%) TAB positive patients had grade 2+ uptake localized to the TA, OA, MA or VA arteries and may have been missed on older generation scans.
Conclusion: This PET/CT protocol had good diagnostic accuracy. The high NPV of 98% indicates that it could be used as a first-line test to rule out GCA.
- Sammel, Arthritis Australia, 2; E. Hsiao, None; G. Schembri, None; K. Nguyen, None; J. Brewer, None; L. Schrieber, None; B. Janssen, None; P. Youssef, None; C. Fraser, None; E. Bailey, None; D. Bailey, None; P. Roach, None; R. Laurent, None.