Phantom Limbs

Another inspired lunch conversation turned its way towards phantom limbs and amputation. Phantom limb pain is a well documented phenomenon, occurring in the majority (up to 80%!) of amputees. From wikipedia: "A phantom limb is the sensation that an amputated or missing limb is still attached to the body and is moving appropriately with other body parts." Sensations in the phantom limb are actually quite complex, and can respond to stimuli (for example, spilling a hot liquid on the non-existant limb). The literature, and associated research, considers this a neurological condition - that is, physically involving the brain and nerve responses.

At the other end of the spectrum is apotemnophilia, or Body Integrity Identity Disorder (BIID), a condition in which a patient has an overwhelming desire to amputate healthy limbs. I've read some pretty horrific stories of patients who were forced to self-amputate (or otherwise remove the limb) when doctors have refused to perform the surgery. In contrast to phantom limbs, BIID is treated as a psychiatric disorder, with no known underlying physical cause.