LIFETIME RISK OF AUTOIMMUNE DISEASE

January 31, 2011 — The first study to determine lifetime risk for inflammatory autoimmune rheumatic disease reports that 1 in 12 women and 1 in 20 men will develop such disorders, and 1 in 28 women and 1 in 59 men will develop rheumatoid arthritis (RA).
The research team, from the Mayo Clinic, Rochester, Minnesota, estimated the lifetime risk for rheumatic disease for both sexes — something that had not been done before. First author Cynthia Crowson, MS, said that prevalence and incidence rates exist, but prevalence figures underestimate individual risk, and incidence rates express only a yearly estimate. The researchers were looking for an accurate basis to offer an easy-to-understand average risk during a person's lifetime, knowing that risk changes at almost every age.
"We were surprised that the lifetime risk is this high," Crowson told Medscape Medical News. "Many people erroneously equate prevalence with lifetime risk, but they are not the same. The prevalence of RA is 1 in 100. These are the first estimates of lifetime risk of RA, so prior to this, the lifetime risk was unknown. However, it was thought to be much smaller." Crowson is a biostatistician at the Mayo Clinic's Department of Health Sciences Research.
The study, reported online December 28, 2010, in Arthritis & Rheumatism, was based on data from the Rochester Epidemiology Project, a long-term epidemiology resource based on patients in Olmsted County, Minnesota. The cohort of 1179 patients diagnosed with any of 7 inflammatory autoimmune diseases between 1955 and 2007 allowed the team to extrapolate the nationwide estimates.
The diseases studied were RA, polymyalgia rheumatica, systemic lupus erythematosus, giant cell arteritis, psoriatic arthritis, primary Sjögrens syndrome, and ankylosing spondylitis.
Table.

Disease	Women	Men
RA	3.6%	1.7%
Polymyalgia rheumatica	2.4%	1.7%
Systemic lupus erythematosus	0.9%	0.2%
Giant cell arteritis	1.0%	0.5%
Psoriatic arthritis	0.5%	0.6%
Primary Sjögrens syndrome	0.8%	0.04%
Ankylosing spondylitis	0.1%	0.6%

"Knowledge of the lifetime risk of RA and of rheumatic diseases is useful because it helps to put the risk of these diseases in context relative to the risks for other diseases," Crowson said. "Clinicians should take note of these numbers in order to provide accurate information to their patients. If patients are concerned about these risks, they may consider lifestyle changes, such as smoking cessation, to lower their risks."
The authors said that these data "have important implications for disease awareness campaigns such as those of the Arthritis Foundation."
Arthritis Foundation President and chief executive officer Jack H. Klippel, MD, told Medscape Medical News that the Crowson study will change the foundation's approach to disease awareness campaigns and should change primary care clinical practice.
"The Arthritis Foundation will use this information as part of our standard messaging. In addition to saying that 1.3 million people in this country have RA, we will be pointing out that the risk [for an autoimmune inflammatory disease] is 1 in 12 for women and 1 in 20 for men. Of course, that risk rises substantially if you smoke or have a family history, and for women begins to approach the risk for breast cancer, which is 1 in 8," Dr. Klippel said.
According to Dr. Klippel, the lifetime risks identified in the Crowson study also suggest that primary care physicians should be considering changes in their approach to RA and related diseases.
"The primary care physician is nearly always the first medical contact for patients with RA, but many (if not most) primary care physicians will tell you that they see few cases of RA. The numbers in this study suggest that early RA is being under-recognized in this setting," Dr. Klippel said.
Dr. Klippel also noted that the 1 in 12 (women) and 1 in 20 (men) baseline risks give physicians a powerful tool for convincing smokers to stop, especially if they also have family histories of RA or related diseases.
Perhaps the most important study limitation, also noted by the researchers, is that the population of Olmstead County is overwhelmingly white, which might limit generalizability to more diverse populations. Dr. Klippel pointed out that this might account for the high risk for polymyalgia rheumatica.
"These risks might reflect both the relatively large number of people of Scandinavian descent, since PMR is more common among Scandinavians, and some degree of referral bias, since the Mayo Clinic is known to have a special interest in PMR," Dr. Klippel commented.
The study was supported in part by a grant from the National Institutes of Health. Ms. Crowson and Dr. Klippel have disclosed no relevant financial relationships.
Arthritis Rheum. Published online December 28, 2010.