Giant cell arteritis (GCA) is a medium to large vessel vasculitis with a predilection for the superficial cranial and intrathoracic arteries. Diagnosing the condition and predicting which patients will develop large vessel complications remains a challenge. There are limitations with temporal artery biopsy, magnetic resonance angiography and ultrasound of temporal arteries and American College of Rheumatology classification criteria.

Positron emission tomography (PET) has been shown to be a useful modality in detecting inflammation in large intra-thoracic vessels but previously has not been able to accurately detect FDG uptake in the superficial cranial arteries due to poor spatial resolution. Newer scanners can perform finer cuts of the head and can detect uptake in these arteries.

This study has three main components:

1. Cross sectional study assessing the accuracy of PET uptake in the superficial cranial and intrathoracic arteries of suspected GCA patients for the diagnosis of GCA
2. Cohort study assessing the prognostic implication of FDG aortic uptake on aortic diameter at 24 months
3. Cohort study assessing the Th1 and Th17 cytokine profile in patients with and without FDG PET uptake at 0, 6 and 24 months

Inclusion Criteria:

• Rheumatologist, neurologist or ophthalmologist suspect diagnosis of GCA

• Age > 50

• Meet at least 2 of 1990 American College of Rheumatology classification criteria for GCA

  1. Age >= 50
  2. ESR >= 50
  3. New onset localised headache
  4. Temporal artery abnormality (tenderness or decreased pulsation)
  5. Positive biopsy (will not be available at time of enrolment)

Exclusion Criteria:

• Corticosteroid therapy for > 72 hours before first PET scan
• Prolonged corticosteroid therapy (> 1 week) for another indication in past 6 months
• History of vasculitis or connective tissue disease
• Active malignancy

Suspected GCA