First was confident in the diagnosis, but he notes that it also raises difficult questions. For instance, if someone simply has extreme ideas, he asks, "Can you call that psychotic or not?"
He has also become a leading expert on an extremely rare condition called body integrity identity disorder, which is characterized by a desire to become disabled, often by becoming an amputee. First says it's similar to the more commonly known gender identity disorder, in which people feel their bodies are the wrong gender, and sometimes have sex-change operations to ameliorate the problem. Because body integrity identity disorder is so rare, First used the Internet to find enough people who feel they were born with a limb they weren't supposed to have to make actual progress on studying the disorder.
Some people who suffer from the disorder and have surgery to become amputees "no longer have the obsession," First says, and hence are—in a sense—cured. "It's totally amazing to try to understand it."