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
Temporal arteritis is caused by transmural inflammation of elastic arteries. It is understood that temporal arteritis is the result of cell mediated immunity which arises as a response to endothelial injury and is antigen-driven disease with T-cell and macrophage activation in the elastic tissue in the arterial walls. The adventitia of the vessel is the initial site of immunologic injury. The 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. The concentric inflammation occurs in segments. Macrophages in the adventia produce interleukin 6. While in the intima and media of the vessel, macrophages produce vascular endothelial growth factor (VEGF) and metalloproteinases which destroy the internal elastic lamina. An increased activated platelets express P-selectin which may cause vessel inflammation and thromboembolic events. Temporal arteritis arises from giant cells, which are fused monocytes cells that are normally involved in the body immune response. 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.
Pathophysiology
Pathogenesis
- It is understood that temporal arteritis is the result of cell mediated immunity which arises as a response to endothelial injury.[21]
- Temporal arteritis granulomatous histopathology has suggested the presence of an antigen-driven disease with local T-cell and macrophage activation in or near elastic tissue in the arterial walls with an important role of the proinflammatory cytokines. [29, 30]
- The adventitia of the vessel is the initial site of immunologic injury. The 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][13]
- The concentric inflammation occurs in segments.[11]
- Macrophages in the adventia produce interleukin 6.[13] While in the intima and media of the vessel, macrophages produce vascular endothelial growth factor (VEGF) and metalloproteinases which destroy the internal elastic lamina.[12][13]
- An increased activated platelets express P-selectin which may cause vessel inflammation and thromboembolic events. [16]
- Temporal arteritis arises from giant cells, which are fused monocytes cells that are normally involved in the body immune response.
- 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: [3, 4][7]18]
- 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.
Genetics
- There is no known genetic cause of temporal arteritis.
Associated Conditions
- Temporal arteritis 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.[22, 23] Other diseases related with temporal arteritis are systemic lupus erythematosus, rheumatoid arthritis and severe infections.[26, 27, 28]
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].