Background/Purpose: The two main forms of large vessel vasculitis (LVV), giant cell arteritis (GCA) and Takayasu’s arteritis (TAK), are clinically heterogenous diseases with variable disease courses. Although ¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) can be used to detect vascular inflammation, there is little data detailing PET activity over time in LVV.

Methods: Patients with TAK or GCA who fulfilled existing classification criteria were recruited into a single-center prospective, observational cohort. Patients could be enrolled at any point in the disease course. All patients underwent FDG-PET at recruitment per a standardized imaging protocol with follow up imaging at ≥6-month intervals whenever possible. Qualitative assessment of FDG uptake was performed via visual assessment of 9 arterial territories each scored on a scale from 0-3, yielding a summary score ranging from 0-27, PETVAS (PET Vascular Activity Score). Higher scores indicate greater global burden of vascular inflammation. Each study was subjectively interpreted by a central reader, blinded to clinical status, as active or inactive vasculitis. Fisher exact and Mann-Whitney U tests were used to compare variables. Linear regression was used to study trends in PETVAS over time.

Results: A total of 322 FDG-PET scans were examined in 121 LVV patients (TAK = 66; GCA = 55). There were 160 FDG-PET scans from TAK patients and 162 scans from GCA patients.

In the first year after diagnosis, 48 patients (TAK = 21; GCA = 27) had at least one PET at a mean disease duration of 175 days (TAK = 146 days; GCA = 197 days). Of these, 37 patients (77%, TAK = 17; GCA = 20) had an active FDG-PET scan. Median PETVAS in the first year after diagnosis was significantly greater in GCA than TAK (22 vs. 17, p < 0.01), but median daily steroid dose at time of imaging was not significantly different between GCA and TAK (10 vs. 7.5mg/day, p = 0.32). One to five years after diagnosis, 68 patients (TAK = 34; GCA = 34) contributed 152 scans (TAK = 68, GCA = 84), and 105 (69%, TAK = 44; GCA = 61) showed active disease. Beyond 5 years, 38 patients (TAK = 27; GCA = 11) contributed 77 scans (TAK = 49, GCA = 28), and 45 (58%, TAK = 27; GCA = 18) showed active disease.

PETVAS scores significantly decreased at a rate of -0.42 PETVAS/year over a mean disease duration of 2.9 years for GCA patients. PETVAS scores did not significantly decrease for TAK patients over a mean disease duration of 6.3 years (FIGURE).

Of 36 patients with ≥3 FDG-PET scans performed >1 year after diagnosis, scans from 13 patients (TAK = 6; GCA = 7) always showed active disease, scans from 3 patients never showed active disease (TAK = 3; GCA = 0), and scans from 20 patients (TAK = 8; GCA = 12) showed active or inactive disease on serial imaging.

Conclusion: Longitudinal patterns of vascular PET activity are different between TAK and GCA. Patients with GCA have a higher burden of vascular inflammation on FDG-PET during the first year of disease compared to TAK. On average, vascular PET activity significantly decreases over time only in GCA. Most patients with LVV continue to have active vasculitis on PET years after diagnosis despite treatment. Changes in PET activity are dynamic, even in later phases of disease, suggesting LVV is a chronic, inflammatory and relapsing disease.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/longitudinal-patterns-of-vascular-inflammation-in-large-vessel-vasculitis/