The exact cause of polymyalgia rheumatica (PMR) isn’t fully understood, but the condition results from an immune system that mistakenly triggers widespread inflammation in the tissues surrounding your shoulders and hips. A combination of genetic susceptibility, immune system dysfunction, and possibly environmental triggers appears to set the process in motion. PMR almost exclusively affects people over 50, with a mean age of diagnosis around 74.
Where the Pain Actually Comes From
PMR doesn’t damage joints themselves the way rheumatoid arthritis does. Instead, the inflammation targets the soft tissues around joints, particularly the fluid-filled sacs (bursae) that cushion your shoulders and hips. Imaging studies consistently show inflammation in the bursae beneath the shoulder blade, around the hip joints, and near the greater trochanter on the outside of the hip. Fluid can also accumulate around the biceps tendon at the shoulder and within the shoulder joint lining itself.
This is why PMR produces that characteristic pattern of deep, aching pain and stiffness in both shoulders and often both hips simultaneously. Some people also develop inflammation around the spine and, less commonly, in the tendons of the hands. The pain is typically worst in the morning, with stiffness lasting more than 45 minutes before easing up.
The Immune System’s Role
PMR is driven by an overactive inflammatory response centered on a signaling molecule called interleukin-6 (IL-6). IL-6 is a chemical messenger that tells the liver to produce acute-phase proteins, activates certain immune cells, and promotes the development of a specific type of inflammatory T cell called Th17 cells. People with PMR have significantly more Th17 cells circulating in their blood compared to healthy individuals, and their immune cells produce abnormally high amounts of the inflammatory substance IL-17.
At the same time, PMR patients have fewer regulatory T cells, which are the immune cells responsible for keeping inflammation in check. This imbalance, too many pro-inflammatory cells and too few regulatory ones, helps explain why the inflammation becomes self-sustaining rather than resolving on its own. Elevated IL-6 levels also account for the systemic symptoms many people experience: fatigue, low-grade fever, weight loss, and a general feeling of being unwell.
Genetic Predisposition
Your genes play a meaningful role in PMR risk. The strongest genetic link involves a group of immune system genes called HLA-DRB1, which code for proteins on the surface of your cells that help the immune system distinguish between your own tissues and foreign invaders. Among PMR patients, 67% carry the HLA-DRB1*04 variant, a rate far higher than in the general population.
Interestingly, the genetic pattern in PMR closely resembles that of giant cell arteritis (GCA), a related condition involving inflammation of blood vessel walls. Both conditions share the same associated region on the HLA-DRB1 gene, which is distinct from the genetic pattern seen in rheumatoid arthritis. This genetic overlap helps explain why 16 to 21% of people with PMR also develop GCA, and why researchers view the two conditions as part of a shared disease spectrum rather than entirely separate disorders.
Who Is Most at Risk
PMR is overwhelmingly a disease of older adults and people of Northern European descent. In population-based studies, 96% of cases occur in white individuals. Women are affected roughly twice as often as men, with about 64% of cases occurring in females. The condition is rare before age 50, and classification criteria specifically require patients to be 50 or older.
The average person diagnosed with PMR is in their mid-70s, though onset in the 50s and 60s does happen. The reasons for the strong age skew likely involve age-related changes in immune function, sometimes called immunosenescence, which makes the immune system more prone to misfiring as it ages.
Environmental Triggers
Because PMR sometimes appears to cluster in time or follow infections, researchers have investigated whether viruses or bacteria might trigger the disease in genetically susceptible people. Parvovirus B19 was an early suspect, but a prospective study tracking new PMR cases over four years found that none of the patients tested had evidence of recent parvovirus infection. The same study found no consistent seasonal pattern in disease onset, which argues against a single widespread environmental pathogen as a trigger.
That said, the idea of an infectious trigger hasn’t been entirely ruled out. It’s possible that multiple different infections or other environmental exposures could activate the immune system in a way that leads to PMR in people who are already genetically predisposed. The trigger may vary from person to person, which would explain why no single pathogen has been consistently linked to the condition.
The Connection to Giant Cell Arteritis
PMR and GCA are closely related, and understanding one helps explain the other. About 16 to 21% of PMR patients develop GCA, and a meta-analysis found that roughly 23% of people newly diagnosed with PMR have evidence of subclinical blood vessel inflammation even without GCA symptoms.
The two conditions share the same genetic background, the same IL-6-driven inflammatory pathway, and the same Th17 cell imbalance. Research has shown that even in people diagnosed only with PMR, specialized immune cells called dendritic cells expressing activation markers can be found in the walls of temporal arteries, the blood vessels most commonly affected in GCA. This suggests a possible continuum where some cases of PMR involve low-grade vascular inflammation that may or may not progress to full GCA.
The practical significance: new or worsening headaches, jaw pain while chewing, scalp tenderness, or vision changes in someone with PMR could signal the development of GCA, which requires more aggressive treatment to prevent vision loss.
How PMR Is Identified
Because there is no single blood test or imaging study that definitively confirms PMR, diagnosis relies on a combination of clinical features. The 2012 classification criteria require three things to be present: age 50 or older, aching in both shoulders, and elevated blood markers of inflammation (CRP or ESR). From there, a point-based scoring system adds weight for morning stiffness lasting more than 45 minutes, new hip pain, the absence of antibodies associated with rheumatoid arthritis, and the absence of pain in smaller peripheral joints like the hands and feet.
Ultrasound imaging can improve diagnostic accuracy by revealing bursitis and joint inflammation in the characteristic PMR pattern. The scoring system with ultrasound reaches about 81% specificity, meaning it correctly rules out PMR in the majority of people who don’t have it. The diagnosis is also supported by a rapid and dramatic response to low-dose corticosteroids, which remains one of the most telling clinical clues.