Temporal arteritis, also called giant cell arteritis (GCA), is caused by an immune system attack on the walls of medium and large arteries, most commonly the temporal arteries that run along the sides of the head. The condition almost exclusively affects people over 50, with a median age of onset around 75. While no single trigger has been identified, the disease results from a combination of genetic susceptibility, immune system dysfunction, and likely environmental factors that together set off a destructive inflammatory chain reaction inside arterial walls.
How the Immune System Attacks the Arteries
The inflammation in temporal arteritis begins when specialized immune cells called dendritic cells, which normally act as sentries in the arterial wall, become abnormally activated. Once switched on, these cells recruit a flood of white blood cells into the artery wall and drive them to produce inflammatory signaling molecules. Two types of immune cells do most of the damage: Th1 cells, which release a powerful inflammatory signal called interferon-gamma, and Th17 cells, which release interleukin-17.
Interferon-gamma is particularly destructive. It triggers smooth muscle cells in the artery wall to release chemical signals that pull in even more immune cells, including large immune cells called macrophages. These macrophages are central to the damage. They release enzymes that break down the structural tissue of the artery, generate toxic oxygen molecules that injure cells, and produce growth factors that cause the inner lining of the artery to thicken. That thickening is what narrows the blood vessel and restricts blood flow, potentially cutting off circulation to the eyes, scalp, or brain.
The process is self-reinforcing. Interleukin-6, one of the key inflammatory molecules in the disease, simultaneously fuels more inflammation while suppressing regulatory immune cells that would normally calm the response down. Meanwhile, a signaling loop involving a molecule called GM-CSF keeps macrophages active and multiplying within the artery wall. This is why temporal arteritis doesn’t resolve on its own and requires aggressive treatment to interrupt the cycle.
Genetic Risk Factors
Certain inherited immune system genes substantially increase susceptibility. The strongest known genetic link is to a gene variant called HLA-DRB1*04. In a large UK study of 225 cases and over 1,300 controls, carrying this variant nearly tripled the odds of developing GCA (odds ratio of 2.69). This gene codes for a protein that helps the immune system distinguish the body’s own tissues from foreign invaders. Variations in it can make the immune system more likely to misidentify normal arterial tissue as a threat.
Not all gene variants increase risk. HLA-DRB1*01 appears to be protective, roughly halving the odds of developing the condition. Another group of variants, collectively called HLA-DR2, also showed a protective effect in a meta-analysis combining 14 studies with over 4,700 participants. The susceptibility pattern traces to specific amino acid positions in the protein these genes produce, at positions 11, 13, and 33, where particular amino acids create a structural shape that may make the immune system more reactive to arterial wall proteins.
These genetic patterns help explain why temporal arteritis is more common in people of Northern European descent, particularly those with Scandinavian ancestry, and relatively rare in other populations.
Age, Sex, and Who Gets It
Age is the single strongest risk factor. Temporal arteritis is virtually unheard of before age 50, and risk climbs steeply with each decade. The median age at diagnosis is about 75, though cases can occur anywhere from the early 50s to 90 and beyond. The reason age matters so much likely relates to how the immune system changes over time. As people age, the balance between inflammatory and regulatory immune cells shifts toward inflammation, and the arterial walls accumulate damage that may make them more vulnerable to immune attack.
Women develop temporal arteritis roughly two to three times more often than men, a pattern consistent with many autoimmune conditions. Hormonal differences and sex-linked variations in immune function are thought to play a role, though the exact mechanism isn’t fully understood.
Possible Environmental Triggers
Researchers have long suspected that infections might trigger the disease in genetically susceptible people, essentially providing the initial spark that activates those dendritic cells in the arterial wall. Varicella-zoster virus (the virus that causes chickenpox and shingles) has received the most attention. Case reports document GCA flares occurring in direct conjunction with shingles outbreaks, with imaging showing new arterial wall inflammation that wasn’t present before the infection. In one documented case, an 84-year-old woman with previously controlled GCA developed a severe relapse with scalp tissue damage during a shingles episode, with both the virus and the arteritis contributing to blood vessel inflammation.
Other infectious agents, including parvovirus B19 and certain bacteria, have been investigated as potential triggers, but no single pathogen has been consistently linked to the disease. Seasonal patterns in diagnosis rates have been observed in some studies, which would support an infectious trigger, though findings have been inconsistent. The current thinking is that infections may act as a match that lights the fuse in people whose genetics and aging immune systems have already created the conditions for disease.
The Link to Polymyalgia Rheumatica
Temporal arteritis and polymyalgia rheumatica (PMR), a condition causing severe stiffness and pain in the shoulders, hips, and neck, are closely related. Between 40 and 60% of people with GCA also have PMR, and 16 to 21% of people initially diagnosed with PMR go on to develop GCA. The two conditions share genetic risk factors and inflammatory pathways, and many experts consider them different expressions of the same underlying disease process.
If you have PMR, the possibility of developing temporal arteritis is something to be aware of. New headaches, scalp tenderness, jaw pain while chewing, or any visual changes in someone with PMR should be evaluated urgently, because these can signal that the inflammation has spread to the arteries.
Why Prompt Recognition Matters
The most serious consequence of temporal arteritis is vision loss. When inflamed, thickened arteries cut off blood supply to the optic nerve or the retina, the damage can be permanent. Even with modern treatment, between 8 and 20% of patients experience some degree of permanent vision loss in one or both eyes. That loss can happen with devastating speed, sometimes without warning, though it’s often preceded by episodes of temporary blurring or vision blackouts that last seconds to minutes.
Those transient visual episodes are a critical warning sign. They represent moments when blood flow to the eye is temporarily interrupted but not yet permanently blocked. Recognizing and treating the condition before that permanent blockage occurs is the difference between preserving and losing sight. High-dose corticosteroids can halt the inflammatory process rapidly, and newer biologic treatments that target interleukin-6 have expanded treatment options for people who can’t tolerate long-term steroids or who relapse when doses are reduced.