In the 1950s, people thought lupus was a rare disease. Then over the years, studies found lupus rates that varied widely. Now, two new studies suggest the disease may be more common than previously thought.
One study looked at lupus cases in Michigan, the other in Georgia, using medical records from a number of sources.
These studies both found higher rates of lupus than previous studies had shown, with especially high rates among black women.
Lupus is characterized by pain and swelling in various parts of the body, including the skin, joints and kidneys. According to the American College of Rheumatology (ACR), the condition is often marked by fatigue, arthritis and fever, and can sometimes lead to severe issues like kidney disease.
Both of these new studies were funded by the Centers for Disease Control and Prevention (CDC) in an effort to take a closer look at rates of lupus in the US, figures that CDC says have varied widely in previous studies.
The Michigan study was led by Emily C. Somers, PhD, of the Division of Rheumatology at the University of Michigan in Ann Arbor, and focused on two counties in the southeastern part of the state with a population of 2.4 million.
Dr. Somers and team gathered data from a variety of sources, including hospitals and private specialists to look for cases of lupus.
After analyzing the data, the researchers estimated that there were 72.8 lupus cases per 100,000 persons. The rate was higher among women — 128.7 per 100,000.
In contrast, the researchers noted that while results varied greatly, the average rate of lupus found in studies from 1965 to 1995 was 23.8 cases per 100,000 people.
Dr. Somers and team noted that the prevalence of lupus was 2.3 times higher in black people than white people and 10 times higher in women than men. The average age at diagnosis was 39.3 years old.
"[Lupus] prevalence was higher than has been described in most other population-based studies and reached 1 in 537 among black female persons," wrote the researchers.
The Michigan study also found that more black patients had kidney disease (40.5 percent) or kidney failure (15.3 percent) than white lupus patients, 18.8 percent of whom had kidney disease and 4.5 percent of whom had kidney failure.
The Georgia study, which was led by S. Sam Lim, MD, of the Division of Rheumatology at Emory University in Atlanta, focused on the Fulton and DeKalb counties, which include the city of Atlanta. These researchers also used a variety of sources, including databases of hospitals and rheumatologists in the counties.
Dr. Lim and team found very similar results to the Michigan team. The Georgia researchers estimated that there were 73 lupus cases per 100,000 people. The rate for women (127.6 per 100,000) was almost nine times higher than the rate for men (14.7). The rate for black women was even higher at 196.2 per 100,000.
The Georgia study also found that black lupus patients were seven times more likely to have kidney failure than white patients.
Both studies focused on limited geographic areas and were based on medical records, not direct contact with patients. Further research is needed to confirm these findings.
It is likely that more research from different parts of the US will follow. However, both sets of researchers stressed the importance of these findings.
"Based on this comprehensive, population-based surveillance program, our data underscore substantial levels of confirmed [lupus] cases and considerable racial disparities in the epidemiology of [lupus]," wrote Dr. Somers and team. "Such data support a focus of medical resources on early diagnosis and improved treatment of lupus nephritis in young black Americans."
These two studies were published in the February issue of ACR's journal Arthritis & Rheumatology. No conflicts of interest were reported in either study.