A sexual arousal in being an amputee, in fantasizing to have the loss of a limb. Can go to the extreme, of actually attempting to become an amputee.
This Is an erotic interest in being, or appearing to be, an amputee.
It does not always go to the extreme, where one arranges for surgery, to actually become an amputee, though its been known to have happened.
This can be simply the restricting of one's limb of choice, to make themselves feel like the limb is gone.
Those who actually do seek such recourse, through deliberate injury to a limb, or seek surgical solutions, is covered under Body Integrity Identity Disorder. (BIID)