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Giant Cell Arteritis (Temporal Arteritis)
Giant Cell Arteritis
Overview
Giant cell arteritis (aka temporal arteritis or Horton disease) is a granulomatous disease with multi-focal arteritis of large arteries (thoracic aorta, subclavian artery, axillary artery, external carotid artery) that affects elderly individuals (especially women > 55 years-old of northern European descent).
Symptoms
Common symptoms include:
– Scalp tenderness (raised, tender temporal artery)
– Vision loss via optic neuropathy.
– Neck and/or jaw pain (jaw claudication, especially with chewing).
– Tongue necrosis (typically unilateral but bilateral can occur).
Epidemiology
Giant cell arteritis is most common in women over 55 years of age of Northern European descent. It is associated with polymyalgia rheumatica in up to 50% of cases.
Diagnosis & Management
- Serious complications include aortic aneurysm, stroke, and blindness.
- Elevation in ESR (Erythrocyte Sedimentation Rate) and other inflammatory markers are used to support a clinical suspicion of temporal arteritis.
- Importantly, high-dose steroids (60 - 80 mg per day) should NOT be delayed awaiting temporal artery biopsy (IV methylprednisolone is often used at the time of diagnosis).
- Temporal artery biopsy will still be reliable after initiation of steroids.
Histopathology
Key elements of the pathogenesis of giant cell arteritis, according to a very generalized model:
- Dendritic cells in the adventitia are activated, perhaps by viruses or other stimuli;
- Activated dendritic cells recruit and activate CD4+T cells.
- CD4+ T cells release pro-inflammatory cytokines and recruit and activate pro-inflammatory macrophages.
- Macrophages secrete growth factors and facilitate migration and proliferation of vascular smooth muscle cells within the intima, which promotes hyperplasia (aka neointimal hyperplasia).
- Additionally, the macrophages form multinucleated giant cells, which secrete various harmful substances, such as ROS, NO, and matrix metalloproteinases (MMP), which destroys the tunica media and internal elastic lamina.
Summary
In summary, the histopathology of giant cell arteritis is characterized by multi-focal segmental panarteritis with:
- Chronic inflammation.
- Granuloma formation.
- Destruction of the tunica media and elastic laminae.
- Tunica intima remodeling and hyperplasia.
- Luminal occlusion – which, as we've seen, can lead to downstream ischemia and tissue damage.
Image Reference
Giant Cell Arteritis