Giant cell arteritis (GCA) is a common granulomatous vasculitis affecting medium to large-sized arteries. It classically presents with involvement of the superficial temporal artery branches, with headache and blindness. Although temporal artery biopsy (TAB) is the gold standard in diagnosing giant cell arteritis, imaging is increasingly playing a role in non-invasive evaluation.
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Terminology
Historically, giant cell arteritis was also known as temporal arteritis or cranial arteritis, given its propensity to involve the extracranial external carotid artery branches such as the superficial temporal artery. Importantly, other large vessels, such as the aorta and upper limb arteries, may also be involved, sometimes without cranial involvement. Thus, the term giant cell arteritis is preferred 30.
Epidemiology
Giant cell arteritis is the most common primary systemic vasculitis. It has an incidence of 20 per 100,000 in individuals over the age of 50 years (200 per million persons per year) 6,30. It typically affects older individuals with patients usually being older than 50 years, with a peak incidence between the ages of 70 and 80 years 3. There is a recognised female predilection (F:M 2:1) 17,30.
Associations
polymyalgia rheumatica: seen concurrently in ~50% of cases 30
Clinical presentation
Clinical presentation is heterogeneous and typically subacute 10,25,30:
headache (75%)
systemic symptoms (e.g. fever, fatigue, weight loss)
jaw claudication (30%)
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arterial symptoms and signs
tenderness over the affected arteries, typically temporal arteries (50%)
palpable nodularity
weak pulse over affected arteries
bruits on auscultation over the affected arteries
clinical features of an aortic aneurysm or dissection if the aorta is involved
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visual symptoms (15%)
transient vision loss (i.e. amaurosis fugax)
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permanent vision loss (e.g. due to anterior ischaemic optic neuropathy, central retinal artery occlusion, ischaemic stroke, etc.)
in such cases, there may be accompanying Charles-Bonnet syndrome
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diplopia due to ophthalmoplegia
most commonly an abducens nerve palsy
other neurological symptoms (30%)
Markers
serum erythrocyte sedimentation rate (ESR): markedly raised (≥50 mm/h) 30
serum C-reactive protein (CRP): often markedly raised (≥10 mg/L) 30
Pathology
It is histologically similar to other large vessel vasculitides (such as Takayasu arteritis) showing granulomatous inflammation of arteries with infiltration predominantly by histiocytes, lymphocytes, and multinucleated giant cells. The characteristic multinucleated giant cells are only found in ~50% of cases 1,30.
Areas of normal superficial temporal artery interspersed within inflamed sections of artery, known as skip lesions, result in false negatives in up to 8-28% of cases 12,13,15.
In a study of 285 patients with biopsy-proven giant cell arteritis there were four main histological patterns 12:
adventitial pattern: inflammatory cells restricted to the adventitia
adventitial invasive pattern: local invasion of the media with preservation of the intima
concentric bilayer pattern: inflammatory infiltration of adventitia and intima with preservation of the media
panarteritic pattern: inflammatory infiltrates in the three arterial layers
Location
Can potentially affect any medium to large-sized vessels. Vessel involvement can be broadly dichotomised into two overlapping phenotypes 27:
cranial giant cell arteritis (C-GCA): classic clinical presentation, particular involvement of the extracranial branches of the external carotid artery, more likely to have a positive temporal artery biopsy 6,27
large vessel giant cell arteritis (LV-GCA): more likely to have an atypical presentation (e.g. more constitutional symptoms), particular involvement of the aorta and its major branches, less likely to have a positive temporal artery biopsy 7,27
Radiographic features
Ultrasound
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increased diameter and hypoechoic wall thickening (halo sign) of the superficial temporal artery (and/or other imaged arteries, e.g. vertebral artery 20, axillary artery 21)
with duplex ultrasound of the superficial temporal artery, sensitivity is 87% and specificity is 96% 9
more specific for giant cell arteritis if bilateral 8
reversible under corticosteroid treatment; this is reflected in the normalisation of the sonographic features
stenosis may be present but is not a specific sign for giant cell arteritis 8
CT
CT may be normal and is inferior to MRI in the diagnostic work-up of giant cell arteritis. Abnormal findings on CT are non-specific and may include:
wall thickening of affected arterial segments
calcification
mural thrombi
Arterial phase CT (angiography) may be useful for assessing luminal abnormalities:
stenoses
occlusions
dilatations
aneurysm formation
MRI
MRI brain with MR vessel wall imaging has a very high negative predictive value in evaluating giant cell arteritis 2, indeed it has been suggested in one study to obviate the need for temporal artery biopsy if the MRI is normal 24. MR vessel wall imaging should be interpreted alongside time of flight angiography to ensure the correct vessels, namely the superficial temporal arteries, are being reviewed.
On MR vessel wall imaging, giant cell arteritis is characterised by mural inflammation in the superficial temporal arteries, best seen on T1 C+ (Gd) sequences, whereby there is mural enhancement and thickening 2. This can be graded as either physiologic (grades 0 and 1) or pathologically indicative of mural inflammation (grades 2 or 3) 2:
grade 0: no mural thickening (<0.5 mm) and no mural contrast enhancement
grade 1: no mural thickening (<0.5 mm) and only slight mural contrast enhancement
grade 2: mural thickening (>0.6 mm) and prominent mural contrast enhancement
grade 3: strong mural thickening (>0.7 mm) and strong mural contrast enhancement
Additionally, MRI brain may demonstrate:
mural involvement, indicating arteritis, of other arteries
complications of mural involvement, e.g. stenoses, occlusions, dilatations, aneurysm formation, ischaemic stroke
enhancement of the temporalis muscle: seen in ~20% of cases 22
orbital inflammation, e.g. optic perineuritis, orbital apex inflammation, inflammataion of the ophthalmic artery 23,30
dural enhancement 29
Nuclear medicine
PET-CT
18F-FDG PET/CT shows vascular 18F-FDG uptake in affected arteries, particularly affected large vessels 26,27. According to one study, the most common arteries where this uptake is demonstrated include 26:
subclavian arteries (~75%)
thoracic and abdominal aorta (~50%)
axillary arteries (~40%)
carotid arteries (~40%)
femoral arteries (~35%)
iliac arteries (~35%)
There may also be concurrent uptake in a pattern consistent with polymyalgia rheumatica, such as within the shoulders and hips 28.
Treatment and prognosis
Treatment is primarily with immunosuppression. Agents that may be used include 11,14,17,18:
corticosteroids (e.g. prednisolone)
tocilizumab (interleukin-6 inhibitor)
methotrexate
secukinumab (interleukin-17 inhibitor)
Aspirin is often used adjunctively for prevention of ischaemic events 19.
Complications
thoracic aortic aneurysms (more commonly ascending aorta) 7
aortic dissection (more commonly ascending aorta) 7
vision loss 17
focal neurological deficits from ischaemic stroke
Differential diagnosis
Imaging differential considerations include:
Takayasu arteritis: affects younger patients (<50 years) and typically affects more proximal vessels