FYI, casting sides are vague, often encrypted, and occasionally deceptive script excerpts that casting agents use to audition actors for small parts without the risk of leaking spoilers. So these details might be straight-up lies, but here's what we think we know:
Tracy: Described as "athletic" and "attractive," she suffers a ischemic stroke and is taken to the ER by Brian, the self-possessed guy she routinely beats at racquetball at the gym. An ischemic stroke, by the by, is a stroke that happens as a result of an obstruction in the blood vessels leading to one's brain.
Rita: Thirty-three weeks pregnant, Rita is risking her life to give birth to a baby, given her own heart malformation. Her husband, Eric, explains to one of the doctors that her determination stems from an earlier tragedy.
Marjorie: An 89-year-old woman, Marjorie has an unspecified condition, the treatment for which results in memory loss. She's distraught that the medicine is causing her to forget her beautiful life, her husband of 65 years, and their time teaching English in Japan.
Robbie: Robbie is a 22-year-old suffering from a kidney stone, arrhythmias, and immense pain.
Grey's Anatomy Season 11 premieres Thursday, September 25, at 8 p.m. ET on ABC.