What is Lupus? A Primer on Selena Gomez's Condition

Known as "the great imitator," lupus is notoriously hard to diagnose because symptoms are similar to so many other disorders. Fatigue, headaches, swollen joints, fever and anemia are some of the most common symptoms -- but there's no one test that can definitively diagnose the condition. Instead, doctors look for inflammation and holistically diagnose based on symptoms and a variety of test results. Though symptoms can be severe and even fatal, in general, serious consequences can be avoided with aggressive treatment.

Selena Gomez Reveals 'Revival' Lyrics

Treating lupus usually involves a variety of prescription medications and even chemotherapy, as Gomez described receiving in her cover story. Lifestyle changes are also important in managing the condition.

Though lupus is not curable, it is possible through treatment to diminish symptoms and avoid permanent organ damage. As Gomez told Billboard, her lupus is in remission.