House repeatedly suspects lupus in House M.D., making it one of the series’ best-known running jokes.
Lupus is an autoimmune disease in which the immune system attacks the body’s own tissues. Because it can affect multiple organs and produce varied symptoms, it is a medically plausible candidate in puzzling multisystem cases, which makes it useful in the show’s diagnostic storytelling.
In many episodes, a doctor proposes lupus during the differential diagnosis, only for House or the team to move on to another explanation. The repetition became a recognizable piece of the show’s dialogue and a popular reference among viewers.
The joke does not mean lupus never occurs in the series. It appears as a real diagnosis in some storylines, including an episode involving a patient with lupus. The recurring phrase is therefore a television motif, not a medical rule that lupus is never the answer.