From the linked article -

Last year, the singer announced that she suffers from Morgellons syndrome, a rare skin condition. It's a controversial diagnosis – many doctors deny that Morgellons is real, calling it delusional. "[It's a] weird, incurable disease that seems like it's from outer space," Mitchell told the Times. "But my health's the best it's been in a while. Two nights ago, I went out for the first time since 23 December."


DeG