Bob Dylan is "a plagiarist", Joni Mitchell said in a rare interview this week, offering cranky comments on old Bob and warm memories of Jimi Hendrix. The legendary singer-songwriter, who has wrestled with health problems, said she may quit music to lobby for recognition of her rare medical condition.

But let's begin with Dylan. Mitchell was speaking to the LA Times as part of a joint interview with performance artist John Kelly, who has performed Mitchell's songs in drag. The Times interviewer referred to Old Nasal Voice in passing, citing his name-change from Robert Zimmerman to Bob Dylan. (Mitchell also abandoned her birth name, Roberta Joan Anderson.) Mitchell launched into an unprovoked assault. "We are like night and day, he and I," she scoffed. "Bob is not authentic at all. He's a plagiarist, and his name and voice are fake. Everything about Bob is a deception."

Cowed, the interviewer moved on to safer topics – such as Prince (apparently a Mitchell fan) and sex appeal. Yet Mitchell still had time to slag off Grace Slick and Janis Joplin (allegedly they were "[sleeping with] their whole bands and falling down drunk"), and Madonna. Railing against the "stupid, destructive" era we live in, Mitchell took aim at the Material Girl. "Americans have decided to be stupid and shallow since 1980. Madonna is like Nero; she marks the turning point."

It wasn't all piss and vinegar. Mitchell fondly recalled Hendrix, "the sweetest guy", and late-night listening sessions together. But even this memory is shaded in frustration. "He made his reputation by setting his guitar on fire, but that eventually became repugnant to him," she recalled. "'I can't stand to do that anymore,' he said, 'but they've come to expect it. I'd like to just stand still like Miles.'"

If Mitchell seems ornery, it may simply be because she is feeling better. 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."

"Garbo and Dietrich hid away just because people became so upset watching them age, but this is worse," she said. "Fibres in a variety of colors protrude out of my skin like mushrooms after a rainstorm: they cannot be forensically identified as animal, vegetable or mineral. Morgellons is a slow, unpredictable killer – a terrorist disease: it will blow up one of your organs, leaving you in bed for a year."

"In America ... [doctors] send you to a psychiatrist," Mitchell explained. "I'm actually trying to get out of the music business to battle for Morgellons sufferers to receive the credibility that's owed to them." Then again, this campaign will need funding. Perhaps Bob Dylan could record a benefit album?