Wired Science has an interesting article on people who amputate healthy limbs:
One day, after years of agony, an Australian man took a large quantity of dry ice and intentionally damaged his left leg, so that a surgeon would have to amputate it.
The action was intentional and the man, Robert Vickers, described the feeling of waking up in the hospital without his leg as “absolute ecstasy.” He’s one of a small number of people who have what psychiatrists have come to call body integrity identity disorder in which patients report the desire to have one or more of their limbs amputated because the extremities don’t feel like they “belong” to their bodies.
The disorder is the subject of a debate between psychiatrists and neuroscientists about whether the brain physiology causes the psychiatric condition or whether the causality runs in the other direction. New research by both sides has yielded fresh ammunition for both interpretations, highlighting how difficult it is to separate biological from psychological phenomena.