There is another disease where people actually amputate their limbs and its called Body Integrity Disorder (BIID) which is a:
Psychological condition in which the individual requests an elective amputation. Individuals with this condition experience the persistent desire to have their body physically match the idealized image they have of themselves. This desire forces individuals to deal with the paradox of losing one or more major limbs (i.e. arm[s] or leg[s]) to become whole. In their minds, "Less is more".
These individuals are not psychotic. In fact, a diagnosis of psychosis
Here is the official web site is any one wishes to gather more information.