Temporal arteritis pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Hamid Qazi, MD, BSc [2]
Overview
The exact pathogenesis of [disease name] is not fully understood.
OR
It is thought that [disease name] is the result of / is mediated by / is produced by / is caused by either [hypothesis 1], [hypothesis 2], or [hypothesis 3].
OR
[Pathogen name] is usually transmitted via the [transmission route] route to the human host.
OR
Following transmission/ingestion, the [pathogen] uses the [entry site] to invade the [cell name] cell.
OR
[Disease or malignancy name] arises from [cell name]s, which are [cell type] cells that are normally involved in [function of cells].
OR
The progression to [disease name] usually involves the [molecular pathway].
OR
The pathophysiology of [disease/malignancy] depends on the histological subtype.
Pathophysiology
Pathogenesis
- It is understood that temporal arteritis is the result of cell mediated immunity which arises as a response to endothelial injury.
- The adventitia of the vessel is the initial site of immunologic injury.
- Activation of dendritic cells in the adventitia causes a production of chemokines that recruit CD4+ T helper cells. The CD4+ T helper cell convert in to Th17 cells which produce interleukin 17 and Th1 cells which produce interferon gamma.
- Giant cell are one of many inflammatory cells that are recruited and produce growth factor which narrows and obstructs the vessels.[10]
- The concentric inflammation occurs in segments.[11]
Intimal macrophages also produce vascular endothelial growth factor (VEGF), which promotes intimal proliferation. Medial macrophages generate metalloproteinases, leading to the destruction of vascular elements, including the internal elastic lamina. [12] Adventitial macrophages produce interleukin-6 (IL-6), augmenting the inflammatory response. This results in inflammation with local vascular damage and intimal hyperplasia, leading to stenosis and occlusion. [13]
A study by Maugeri et al showed that patients with GCA had increased expression of platelets expressing P-selectin, of platelet-Nph and platelet-Mo aggregates, and of Nph and Mo expressing tissue factor. [15] Activated platelets and white cells could cause vessel inflammation and thromboembolic events. [16]
- Temporal arteritis arises from giant cells, which are [cell type] cells that are normally involved in [function of cells].
Genetics
- [Disease name] is transmitted in [mode of genetic transmission] pattern.
- Genes involved in the pathogenesis of [disease name] include [gene1], [gene2], and [gene3].
- The development of [disease name] is the result of multiple genetic mutations.
Associated Conditions
The disorder may coexist (in one quarter of cases) with polymyalgia rheumatica (PMR), which is characterized by a sudden onset of pain and stiffness in muscles (pelvis, shoulder) of the body and seen in the elderly. Other diseases related with temporal arteritis are systemic lupus erythematosus, rheumatoid arthritis and severe infections.
Gross Pathology
- On gross pathology, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].
Microscopic Pathology
- On microscopic histopathological analysis, [feature1], [feature2], and [feature3] are characteristic findings of [disease name].
Pathophysiology
The damage to the vasculature is mediated by an attack on the internal elastica lamina by activated CD4+ T helper cells. This occurs in response to the presentation of an antigen by macrophages. The inciting antigen has not been identified.
Because the disease involves only arteries with internal elastic lamina, the aortic arch and its branches are often involved. Intracranial arteries do not have internal elastic lamina and are not involved. The distribution of involved arteries are as follows:
Commonly involved sites:
- Cervicocephalic arteries: Carotid artery and vertebral artery. The vertebral artery is involved as frequently as the temporal artery in fatal cases. Involvement of the basilar artery is rare.
- Intraorbital branches: Posterior ciliary artery and ophthalmic artery.
- External common, external, and internal carotid artery involvement: It is less common for proximal intracranial arteries to be involved.
- External vertebral arteries: It is less common though for the disease to extend more than 5 mm beyond the dural penetration.
- Subclavian, axially and proximal brachial artery: There can be typical vasculitic lesions with long, smooth, lesions with tapered occlusions.
- Coronary arteries: For a full discussion of the involvement of the heart in this disorder see the chapter on The Heart in Temporal Arteritis / Giant Cell Arteritis
Less commonly involved sites:
- Descending aorta: Mesenteric, iliac, femoral and renal arteries are less often involved. In these cases mesenteric ischemia, renal infarction, and ischemic mononeuropathy can occur.