Giant Cell Arteritis (GCA) Classification

The 2022 ACR/EULAR GCA criteria require two absolute conditions before scoring: (1) a confirmed diagnosis of medium- or large-vessel vasculitis, and (2) age 50 or older at diagnosis. Patients under 50 with large-vessel vasculitis are evaluated under the Takayasu arteritis criteria instead.

Both GCA and Takayasu arteritis (TAK) are large-vessel vasculitides affecting the aorta and its branches, but they differ primarily by age of onset. GCA predominantly affects patients over 50, while TAK typically occurs under 40 and almost always under 60. There is an age overlap zone between 50 and 60 where both criteria sets may be applicable - clinical judgment and the overall pattern of disease involvement are essential in this group.

Yes. The biopsy/ultrasound item carries the most weight (+5), but a score of 6 can be reached without it. For example, ESR/CRP elevation (+3), jaw claudication (+2), and new temporal headache (+2) would reach a score of 7. The criteria are designed to allow classification in settings where temporal artery biopsy or ultrasound may not have been performed.

The FDG-PET criterion requires diffuse FDG-PET activity throughout the aorta - specifically, increased FDG uptake along the thoracic and/or abdominal aortic wall, consistent with active large-vessel vasculitis. Focal or limited uptake not consistent with aortitis does not satisfy this criterion.

These are classification criteria, not diagnostic criteria. They were designed to define homogeneous patient populations for clinical research. Classification and clinical diagnosis are distinct: a patient may be classified as GCA for research purposes while the clinical diagnosis requires broader judgment, and vice versa. A score below the threshold does not rule out GCA, and a score at or above threshold does not confirm it in isolation.