Several risk factors are associated with polymyalgia rheumatica (PMR). These risk factors, as well the possible causes of PMR are described below.

Advanced age. The risk of PMR is known to increase with age. The condition is rarely seen in people under 50 years of age. Most cases involve people 75 years and older. ¹ Mackie SL. Polymyalgia rheumatica: pathogenesis and management. Clinical Medicine [serial online]. August 2013;13(4):398-400.
Female sex. Women are approximately 2 to 3 times more likely to be affected by PMR than men. ² Michet Clement J, Matteson Eric L. Polymyalgia rheumatica BMJ 2008; 336 :765
Northern European descent. People of any ethnicity can develop PMR. However, Caucasian people of northern European descent appear to be at a significantly higher risk. ³ Nuenninghoff DM, Hunder GG, Christianson TJ, McClelland RL, Matteson EL. Incidence and predictors of large-artery complication (aortic aneurysm, aortic dissection, and/or large-artery stenosis) in patients with giant cell arteritis: A population-based study over 50 years. Arthritis Rheum 2003; 48 : 3522-31. As cited in - Milchert M, Brzosko M. Diagnosis of polymyalgia rheumatica usually means a favourable outcome for your patient. Indian Journal Of Medical Research [serial online]. May 2017;145(5):593-600.

Not everyone with these risk factors will develop PMR. The presence of these risk factors only increases the likelihood of developing PMR.

Possible Causes of Polymyalgia Rheumatica

Several potential causes for PMR are being investigated. Some of the theories put forward by researchers include:

Genetic predisposition. A specific gene called HLA-DR4 that is associated with rheumatoid arthritis is also present in many cases where PMR and giant cell arteritis occur together. Experts speculate this gene triggers the condition, although this is not a conclusive cause in PMR. ⁴ Cimmino MA. Genetic and environmental factors in polymyalgia rheumatica Annals of the Rheumatic Diseases 1997;56:576-577. ^, ⁵ Cimmino MA, Zaccaria A. Epidemiology of polymyalgia rheumatica. Clin Exp Rheumatol 2000; 18:S9-11; PMID:10948749
Immunology. Blood tests indicate immune system cells penetrating the synovial membrane of joints and tendons, resulting in inflammation. This is similar to the autoimmune process in which the body tissues are attacked by its own immune system. ⁴ Cimmino MA. Genetic and environmental factors in polymyalgia rheumatica Annals of the Rheumatic Diseases 1997;56:576-577.
Infection. The sudden start of PMR and the nature of the symptoms like joint pain, fever, and malaise, are suspected to be a result of infections caused by viruses. ⁴ Cimmino MA. Genetic and environmental factors in polymyalgia rheumatica Annals of the Rheumatic Diseases 1997;56:576-577.
Environmental factors/exposure to sunlight. Damage of superficial arteries by over exposure to ultra violet radiation from the sun is another proposed cause for the development of PMR. Some studies suggest the elastic fibers present in the arteries and synovial membranes are damaged by ultra violet rays. These damaged tissues may get infected by viruses that remain dormant for a long time and may get reactivated later, causing PMR. ⁴ Cimmino MA. Genetic and environmental factors in polymyalgia rheumatica Annals of the Rheumatic Diseases 1997;56:576-577.

These same risk factors and possible causes are also seen in giant cell arteritis. Expert analysis indicates 40% to 60% of giant cell arteritis cases eventually develop PMR. There is also a 9% to 20% risk of PMR cases developing giant cell arteritis. ⁶ Gonzalez-Gay MA. Giant cell arteritis and polymyalgia rheumatica: two different but often overlapping conditions. Semin Arthritis Rheum 2004 Apr; 33 (5): 289-93 As cited in - Schmidt J, Warrington K. Polymyalgia Rheumatica and Giant Cell Arteritis in Older Patients. Drugs & Aging [serial online]. August 2011;28(8):651-666. Diagnostic tests of blood samples and genetic components reveal similar findings for PMR and giant cell arteritis, leading experts to see these conditions as two ends of the same disease spectrum.