What Causes Polymyalgia Rheumatica and Who Gets It?

Polymyalgia rheumatica (PMR) is an inflammatory condition whose exact cause remains unknown, but the best current evidence points to a combination of genetic susceptibility, immune system dysregulation, and possibly environmental triggers acting together in people over 50. It overwhelmingly strikes older adults of Northern European descent, especially women, and its hallmark is severe, symmetric stiffness and aching in the shoulders, hips, and neck that appears seemingly out of nowhere. Despite decades of research, there is no single smoking gun, and the picture that has emerged is more of a slow-burning autoimmune misfiring than a clear infection-driven or injury-driven disease.

Who Gets PMR

PMR is almost exclusively a disease of older adults. Population-based studies consistently find that nearly all cases occur in people aged 50 and older, with incidence climbing steeply through the sixties and peaking in the 70–79 age group before declining somewhat after 80.¹ If you are under 50, a PMR diagnosis is extremely unlikely, and most clinicians would look hard for alternative explanations before considering it.

Women are affected roughly twice as often as men. A German review reported incidence rates of about 22 per 100,000 in women compared with about 13 per 100,000 in men.² Why women are more vulnerable isn’t fully understood, but the pattern mirrors many other autoimmune and inflammatory conditions where hormonal and immune differences between sexes play a role.

Geography and ancestry matter too. PMR is far more common in populations of Northern European background, and a large cohort study of women found that Scandinavian ancestry more than doubled the risk compared to other European ancestry.³ That same study found that living in the northeastern United States was associated with higher risk compared to the Midwest, while living in the South or West was not. This geographic clustering hints at a combination of shared ancestry genes and possibly environmental factors like sunlight exposure, though disentangling the two is difficult.

The Genetic Side

PMR runs in some families, and researchers have long suspected that genes in the HLA (human leukocyte antigen) region on chromosome 6 play a role. HLA genes help your immune system distinguish your own tissues from foreign invaders, and variations in these genes are linked to many autoimmune conditions. In one well-known study of PMR patients, the HLA-DRB1*04 allele was found in about two-thirds of cases.⁴ But the genetic picture isn’t as clean as it is for some other diseases. The specific HLA associations vary from one population to another, which means the genetic risk for PMR in Scandinavians may involve different gene variants than in Southern Europeans.⁵ An Italian study, for example, found no significant differences in HLA-DRB1 frequencies between PMR patients and healthy controls in that population.⁶

More recent genome-wide work has expanded the genetic map beyond HLA. A large meta-analysis identified three novel gene regions associated with PMR susceptibility, in genes called IL1R1, NEK6, and CCDC88B, alongside confirmation of the known HLA-DRB1 association and a locus near ANKRD55.⁷ IL1R1, for instance, encodes a receptor for the inflammatory signaling molecule interleukin-1, which fits neatly with what researchers already know about elevated inflammatory cytokines in PMR. The takeaway is that no single gene causes PMR, but carrying certain variants can tilt the odds, especially in combination with environmental exposures.

Modifiable Risk Factors

Genetics is not destiny, and a genuinely surprising finding from Mendelian randomization analysis is that at least two modifiable lifestyle factors appear to influence PMR risk. That same genome-wide meta-analysis found that genetically predicted smoking intensity was associated with about a 32% increase in PMR susceptibility, and genetically predicted visceral adiposity (belly fat, essentially) was associated with roughly a 22% increase.⁷ Mendelian randomization uses genetic variants as stand-ins for exposure to test causal direction, so these aren’t just correlations in a questionnaire. Smoking and carrying excess visceral fat both promote chronic low-grade inflammation, so the connection makes biological sense. Neither guarantees you’ll develop PMR, but both appear to raise the bar your immune system has to clear before tipping into disease.

Do Infections or Seasonal Factors Trigger PMR?

One of the longest-running debates about PMR is whether an infection kicks it off. The idea is appealing: many patients recall the disease starting abruptly, sometimes after a flu-like illness, and early studies noticed seasonal clustering. A British study from 1990 found that about 62% of PMR cases developed between May and August, and onset correlated with outside temperature and hours of sunshine.⁸ The researchers speculated that seasonal infections or even sun-related damage to superficial blood vessels might be involved.

But decades of follow-up research have been deeply mixed. A narrative review of the infection literature concluded that while the hypothesis is biologically plausible, most studies are retrospective and cannot nail down a causal relationship. A recent systematic review and meta-analysis found that the pooled incidence rate ratio for onset in warm versus cold seasons was not significant, suggesting that the seasonal pattern, if it exists at all, is not robust across populations.⁹ Specific pathogens like parvovirus B19, Mycoplasma pneumoniae, and Chlamydia pneumoniae have all been investigated as potential triggers, but none has been consistently linked to PMR across multiple studies. The honest summary is that infections might push a genetically susceptible person over the edge, but there is no proven infectious cause.

What Goes Wrong in the Immune System

Even without knowing the initial trigger, researchers have a reasonable picture of what the immune system is doing wrong in PMR. The inflammation is not random. It concentrates in very specific places: the bursae (fluid-filled sacs that cushion joints), the synovial lining of joints, and the sheaths surrounding tendons, particularly around the shoulders and hips. MRI studies consistently show subacromial bursitis, joint effusions, and peritendinitis at strikingly high rates. One study found subacromial-subdeltoid bursitis in nearly 88% of shoulders examined and peritendinitis in 100% of hips.¹⁰ The inflammation is also accompanied by soft tissue edema that distinguishes PMR from other conditions like rheumatoid arthritis on imaging.¹¹

At the molecular level, the process involves a cascade of inflammatory signaling molecules, particularly interleukin-6 (IL-6). In PMR, activated cells in the synovial lining secrete IL-6, which promotes further proliferation of those cells and drives up acute-phase reactants in the blood, creating the systemic inflammation that makes patients feel so unwell.¹² Other inflammatory cytokines like interleukin-1, interleukin-17, and tumor necrosis factor-alpha are also elevated.

A key feature of PMR is an imbalance between two types of immune cells. Regulatory T cells (Tregs), which normally keep inflammation in check, are decreased, while Th17 cells, which promote inflammation, are increased.¹³ This shift helps explain why the disease produces such powerful systemic inflammation. The encouraging news is that corticosteroid treatment appears to restore this Treg/Th17 balance, which tracks with the dramatic clinical improvement most patients experience.¹⁴

PMR and Giant Cell Arteritis

PMR has a close and complicated relationship with giant cell arteritis (GCA), a condition where inflammation targets the walls of large arteries, particularly those in the head. Both diseases affect the same demographic (older adults, women, Northern Europeans), both produce systemic inflammation, and both respond to corticosteroids. In patients with biopsy-proven GCA, PMR symptoms are present in up to half of cases, and PMR can be the initial presentation before the classic cranial symptoms of GCA (headache, jaw pain, vision changes) appear.¹⁵

The overlap raises a practical question: if you have PMR, do you also have silent GCA? A prospective study found that about 20% of patients initially diagnosed with PMR had subclinical vascular inflammation that later progressed to classical GCA.¹⁶ That finding supports the view that PMR and GCA may sit on a spectrum of the same inflammatory process rather than being two separate diseases that sometimes coexist. For patients, the implication is straightforward: if you develop new headaches, scalp tenderness, jaw pain when chewing, or any vision changes while being treated for PMR, contact your doctor immediately, because those symptoms may signal GCA progression, which can threaten eyesight.

Why Diagnosis Can Be Tricky

There is no single blood test or imaging study that definitively diagnoses PMR. Doctors rely on a combination of clinical symptoms, elevated inflammatory markers, and response to treatment. Most patients have elevated erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP), but about 15% of confirmed PMR patients have normal levels of both markers, which can delay diagnosis.¹⁷ If a doctor relies too heavily on blood tests to rule PMR in or out, a meaningful minority of patients will be missed.

Another diagnostic challenge is distinguishing PMR from elderly-onset rheumatoid arthritis (EORA), which can present with identical polymyalgic symptoms in the early stages. Anti-CCP antibody testing helps here: one study found these antibodies in 65% of EORA patients but in none of the PMR patients tested, making a positive result a strong signal toward rheumatoid arthritis rather than PMR.¹⁸ A rapid and dramatic response to low-dose corticosteroids has traditionally been considered almost diagnostic for PMR, but the time frame is more variable than textbooks suggest. Some patients improve within 12 hours, while others don’t reach adequate relief for three to four weeks.¹⁹ Using a rigid timeline for steroid response can lead to premature abandonment of the diagnosis in patients who are simply slower to respond.

Relapse and the Long Steroid Problem

PMR is highly treatable with corticosteroids, but it is not a quick-fix disease for many people. The standard approach is to start low-dose prednisone and gradually taper over months, ideally discontinuing within one to two years. In practice, relapses are common and many patients end up on steroids far longer than anyone would like. A systematic review and meta-analysis found that female sex, elevated inflammatory markers, peripheral arthritis, the starting steroid dose, and the speed of tapering were the most frequently studied predictors of relapse, though results across studies were inconsistent.²⁰

A multicenter study of 185 patients offered some clearer findings. Starting on a higher dose of corticosteroids and reducing the dose faster both significantly increased the risk of relapse. Interestingly, patients with a prior history of dyslipidemia (high cholesterol or triglycerides) had roughly half the relapse risk, a puzzling association that may reflect statin use or some other metabolic factor, though the mechanism is unknown.²¹ The practical lesson is that patience with tapering appears to pay off: cutting the dose too aggressively is one of the clearest drivers of flare-ups.

For patients who keep relapsing or can’t tolerate long-term steroids, newer options are emerging. Tocilizumab, a drug that blocks the IL-6 receptor, has shown promise in pooled analyses. A systematic review and meta-analysis found that tocilizumab significantly reduced both short-term and longer-term relapse rates compared to placebo and lowered the total steroid burden patients needed.²² Given that IL-6 is central to the inflammatory cascade in PMR, targeting it directly makes mechanistic sense and may eventually change the standard treatment approach for patients who struggle with steroids alone.

The Gut Connection and Emerging Research

One area of early-stage research is whether the gut microbiome plays a role in PMR. The broader theory is that gut bacteria influence systemic inflammation through their effects on immune cell development, and disruptions to the microbial balance have been implicated in a growing list of inflammatory conditions. PMR has been included among diseases with a suspected gut-microbiota relationship, though the evidence remains largely theoretical and drawn from general principles of immune regulation rather than from PMR-specific clinical trials.²³ There are no diet-based treatments for PMR with proven efficacy, and claims about probiotic or dietary interventions for this specific condition should be treated with skepticism until clinical data catch up with the hypothesis.

Research into the dendritic cell pathways that drive arterial inflammation in GCA is also shedding indirect light on PMR. A recent study examining arterial tissue from GCA patients found that monocytes differentiated into mature dendritic cells directly within the arterial wall, a process far more active in GCA arteries than in PMR or control arteries.²⁴ This distinction helps explain why GCA produces the destructive vascular complications that PMR generally does not, and it reinforces the idea that although the two conditions share an inflammatory starting point, the downstream tissue damage diverges. Understanding where the shared pathway branches into vessel-damaging GCA versus the joint-and-bursa-centered inflammation of PMR is one of the most active areas of research, with implications for earlier detection of patients at risk of progressing from one to the other.