Autoimmune diseases — conditions in which the immune system mistakenly attacks the body’s own tissues — affect as many as 50 million Americans and millions more worldwide, and their prevalence is increasing, according to the Associated Press. The diseases range from lupus and rheumatoid arthritis to Type 1 diabetes and multiple sclerosis. They share a common diagnostic challenge: symptoms that overlap with other illnesses, making correct identification difficult and often slow.

Lupus, one of the most widely recognized autoimmune conditions, illustrates the difficulty. The disease is nicknamed “the disease of 1,000 faces” because its symptoms — rashes, swelling, fevers, joint pain, and organ damage — vary so widely from patient to patient that no two cases present identically, making identification difficult even for experienced physicians.

Ruth Wilson of Massachusetts experienced that difficulty for years. Doctors misdiagnosed or dismissed her rashes, swelling, fevers, and severe pain over a six-year period, she told the Associated Press. Wilson said she saved her own life by demanding one more test in an emergency room that was preparing to send her home, again, without answers.

That test revealed her kidneys were failing. The cause was lupus — her immune system had been attacking her own body, undetected, for years.

“I just wish there was a better way that patients could get that diagnosis without having to go through all of the pain and all of, like, the dismissiveness and the gaslighting,” Wilson said.

Autoimmune diseases encompass a broad category of more than 80 recognized conditions in which the body’s immune system, which normally fights infection, turns against the body’s own tissues. The diseases disproportionately affect women, and researchers say their incidence is rising, though the underlying reasons are not fully understood.

Diagnosis is complicated by the fact that many autoimmune conditions share overlapping symptoms with one another and with non-autoimmune illnesses. No single test confirms most forms of the disease. Physicians often must rule out multiple conditions before arriving at a diagnosis, a process that can take months or years.

The diseases remain among medicine’s biggest mysteries, with treatments that are often limited to managing symptoms rather than addressing root causes, according to the Associated Press.