No causes of polymyalgia rheumatica (PMR) have yet been identified. The inflammation associated with PMR is known to be caused by the white blood cells attacking the synovium (lining of the joints), but why they do this is unknown.

There are certain factors that seem to increase the risk of developing PMR. These include:

• Genetics, race and sex. White women are affected more often than any other demographic. People of Northern European descent seem to be particularly at risk. This suggests that there may be a genetic susceptibility in certain individuals to PMR, but no research has been able to identify a particular genetic link.
  
  
• Age. Incidences of PMR in individuals under the age of 50 are extremely rare. Many researchers have suggested that PMR may be connected to the aging process. How it might be connected and to what degree remains controversial.
  
  
• Immune system abnormalities. The attack on the synovium by the white blood cells appears to be due to abnormalities in the immune system. The cause is not known.
  
  
• Climate. PMR is more prevalent in cooler climates. It is not known whether this is due to an environmental effect on PMR susceptibility or to the genetic background of the people who live in these environments.
  
  
• Viruses. Some research has indicated a possible link between PMR and certain viruses, such as adenovirus (any of a group of viruses that cause upper respiratory tract infections and conjunctivitis) and fifth disease (a viral disease that is usually mild and typically occurs in childhood).