"The idea behind erotic identity disorders—that sometimes the sexual object can be inverted into the self"

I do not think that these are "disorders", rather just unusal ideas that can become fetishized. 

Apotemnophilia - A paraphilia of the stigmatic/eligibilic type in which sexuerotic arousal and facilitation or attainment of orgasm are dependent upon oneself being an amputee. In this disorder, otherwise sane and rational individuals express a strong and specific desire for the amputation of a healthy limb or limbs. Most date this desire to their childhood and not uncommonly the sufferer will attempt to obtain amputation of the specific limb. As few surgeons are willing to amputate healthy limbs, this often means that the patient themselves will attempt to irrevocably damage the limb in question, thus necessitating formal amputation. After amputation most report to being happy with their decision and often state, paradoxically, that they are ‘complete’ at last.

Autonepiophilia -  a sexual fetish for some that involves a regression to an infant-like state. Behaviors may include drinking from a bottle or wearing diapers. Individuals may engage in gentle and nurturing experiences (an adult who only engages in infantilistic play is known as an adult baby) or be attracted to masochistic, coercive, punishing or humiliating experiences. Diaper fetishism involves "diaper lovers" wearing diapers for sexual or erotic reasons but may not involve infant-like behavior. Individuals who experience both of these things are referred to as adult baby/diaper lovers (AB/DL). When wearing diapers, infantilists may urinate or defecate in them.

There is no recognized etiology for infantilism and little research on the subject. It has been linked to masochism and a variety of other paraphilias. A variety of causes has been proposed, including altered lovemaps, imprinting gone awry and errors in erotic targets, though there is no consensus. A variety of organizations exist to promote infantilism or meet with other practitioners throughout the world.