These are patients who had exhausted all proven therapeutic options or who had an extremely rare diagnosis. (mottchildren.org)
These two collections of stories about rare diagnoses both have links to the TV series House. (newscientist.com)
He spent his first year living with one rare diagnosis (1/100, 000 chance) before doctors realized, with more testing, that he actually has an altogether different rare condition (they don't even know of 25 kids that have it). (believemidwiferyservices.com)