It’s called Body Integrity Identity Disorder, or BIID for short, and is a psychological ailment that affects the mind of the sufferer. Why exactly would anyone want to cut off his or her own body parts? Scientists believe there are several reasons. One theory is that the neurons in the brain fail to effectively communicate as they should, thus not incorporating a certain part of the body.
When a sufferer of BIID sees the part of their body that they fail to understand because of their neurons, they believe it is not supposed to be there and feel as though they look deformed. Because the brain cannot deliver a correct plan of the body they feel incomplete unless the limb is missing!
Another theory is that it has little to do with neurons and is simply a matter of self-consciousness. Just like most people look in the mirror and wish for some physical change, so do sufferers of BIID, just to an extreme level.
They are so unhappy with an aspect of their body that they hope to amputate it. Only extreme cases actually cause themselves bodily harm, while most are simply driven nearly crazy with the desire to have the body part gone. Unfortunately for sufferers of BIID, no doctors will accommodate the amputation desired on legal grounds.