(CNN) Lupus is unpredictable, triggering different symptoms in different patients. A chronic illness, it can even attack many different parts of the body.
The condition is an autoimmune disease, which means that a person's immune system—the body system that usually fights infections—attacks healthy tissue instead. It can cause inflammation and pain anywhere in a patient's body.
Because the illness can look different in every patient, it can go undetected and undiagnosed for years.
The Lupus Foundation of America estimates that 1.5 million Americans and at least 5 million people worldwide have some form of lupus. There are four forms in all: systemic lupus erythematosus (SLE), lupus confined to the skin, lupus caused by some prescription drugs and a rare lupus that affects infants of women with the disease.
Despite ongoing research into how the disease manifests in patients and what causes it, scientists and other experts sometimes describe the disease as cruel mystery -- which is to say, they still have a lot to learn about it.
"There is a lot about lupus that is still a conundrum to us," said Dr. Karen H. Costenbader, a professor of medicine at Harvard Medical School and director of the Lupus Program at Brigham and Women's Hospital in Boston.
"It's treatable, but it can still be very painful and challenging to overcome," said Costenbader, who is also chair of the Lupus Foundation of America's Medical-Scientific Advisory Council.
May 10 is World Lupus Day, and we recently caught up with Costenbader to learn more about the disease.
This conversation has been edited and condensed for clarity.
CNN: What does it mean that lupus is an autoimmune disease?
Dr. Karen Costenbader: It means the immune system is attacking healthy tissue inside the body instead of infections. With lupus, patients make antibodies against any different number of organs, cells, internuclear proteins and intercellular particles.
Any organ system can be involved. As a result, causes a wide range of different symptoms that can come and go over time and vary from person to person. These include extreme fatigue, pain or swelling in the joints, low-grade fevers and damage to internal organs like the kidneys, heart and lungs. That's what makes it so difficult to diagnose and treat.
CNN: If lupus presents so differently in every patient, how do experts diagnose it?
Costenbader: The one thing all lupus patients have in common is that they have dealt with chronic pain and discomfort for a while. When lupus first presents, symptoms can include fever, joint pain and rashes. These symptoms are similar to symptoms of infections and other autoimmune diseases such as rheumatoid arthritis, so a diagnosis can be tricky. It takes an astute clinician and expert. Sometimes it also takes time—(recent) research indicates it can take as long as (almost seven) years. As soon as symptoms involve three or more different organ systems, clinicians should start thinking about lupus.
CNN: What is the treatment? Does hydroxychloroquine, the drug that we learned doesn't work for Covid-19, really work on lupus?
Costenbader: Thankfully, today we have more and more treatments through clinical trials. Historically, though, the treatment has been hydroxychloroquine, the same drug that was touted for a while as a potential treatment for Covid-19. It turns out the drug doesn't work for Covid, but it does work well for lupus.
Last year during the pandemic, when people thought it worked for Covid, we had huge shortages of hydroxychloroquine, which was a problem for our patients. Anti-malaria drugs also help stabilize the disease, and steroids work, too. Steroids have a lot of side effects such as weight gain and glaucoma. The goal of some of the new treatments—they're all immunosuppressants—is to keep organ involvement under control.
CNN: Are men or women more likely to get lupus?
Costenbader: Lupus mainly strikes females—nine of 10 people with lupus are female. It also commonly starts between ages 15 to 44 years. We don't know why this happens; it is one of the conundrums. A lot of autoimmune diseases have sex predilections. With lupus, incidence picks up during menstruation, decreases after menopause. Men who have two X chromosomes also have a high prevalence of lupus, so perhaps X chromosomes have something to do with it. This is one of the aspects of the disease we're still studying.
CNN: What are some of the other conundrums experts have identified about lupus?
Costenbader: Lupus is two to three time more common among people of color—African Americans, Hispanics/Latinos, Asians, Native Americans, Alaska Natives, Native Hawaiians and other Pacific Islanders—than among people of European ancestry. The real burden in this country is in young African American women. Lupus is one of the top 5 causes of death of young African American women. We're just starting to have large enough populations involved in the studies to see that the genetics involved with patients may be different.
CNN: Is lupus contagious?
Costenbader: It's not contagious. But it does run with other autoimmune diseases—people who have lupus usually have family members with rheumatoid arthritis and other autoimmune diseases. For people who have lupus, relatives have a 5 to 20% chance of also developing it. Experts think it may develop in response to certain hormones (like estrogen) or environmental triggers.
An environmental trigger is something outside the body that can bring on symptoms of lupus or make them worse. For instance, we know smoking increases the risk of lupus and oral contraceptives might trigger it as well. Obesity, stress and post-traumatic stress disorder can be triggers. We know that if people have a genetic predisposition and they are in the wrong environment, their inflammatory pathways get triggered, and they are at risk.
CNN: What is the outlook for someone with lupus?
Costenbader: Lupus is not a death sentence. With the right meds, and the right physicians and caregivers involved, lupus patients can have kids, hold jobs, and lead productive lives like anybody else.