In 1997 Robert Smith, a surgeon at the Falkirk and District Royal Infirmary in Scotland, fulfilled one of his patient's deepest desires: he amputated the lower part of the man's left leg. Smith performed a similar operation on a German retiree two years later, the British daily The Independent reported in 2000. Neither procedure was medically necessary. Both patients had told Smith that one of their legs was superfluous and that its mere presence had caused them enduring emotional pain.

Psychiatrists estimate that several thousand people worldwide, most of them male, wish to get rid of a normal healthy limb; a smaller number actually request its surgical removal. Such radical requests stem from an extremely rare psychiatric illness called body integrity identity disorder (BIID).

Other names for the condition include amputee identity disorder and apotemnophilia, meaning "amputation love." People with BIID report that a particular limb simply does not belong to them and that they suffer because they feel "overcomplete."

For such individuals, the wish to cut off a limb is not an idle fantasy but an obsessive need to extricate an alien appendage from their body. Many are distressed by such thoughts, which can disrupt their social life and distract them at work. The disorder can even be disfiguring or deadly: those who cannot afford or find willing surgeons may mutilate themselves by, for example, crushing a leg under weights, sawing off a finger or toe, placing the offensive limb in the way of an oncoming train, or packing the body part in dry ice in an attempt to freeze it to death.

As bizarre as such attempts may seem, recent research suggests that people with BIID are not delusional. Although early work hinted that BIID was induced by a sexual fetish with amputation, researchers have now largely turned to other explanations. One theory is that BIID patients long for disability as a way to gain attention that they lacked in childhood. Other research findings indicate, however, that the ailment arises from a neurological conflict between a person's anatomy and his or her body image. Such a conflict could stem, for example, from damage to a part of the brain that constructs the body image in maplike form.

No medication or psychotherapy technique has yet worked to dampen the pathological yearnings of people with BIID. Surgery, on the other hand, has apparently helped in some cases. Rather than resorting to such drastic measures, however, most doctors are hoping that scientific advances will lead to ways of correcting the underlying psychiatric problem, quenching the thirst for amputation before it leads to disability.

Defining the Desire
Since the late 1800s physicians and researchers have written about men and women who pretend to be or would like to become disabled. In 1977 the late sex researcher John Money and his colleagues at Johns Hopkins University described two individuals who wanted to become amputees because they found the idea sexually arousing. Money defined their problem as apotemnophilia, a sexual deviation, or paraphilia, in which a stump, pair of crutches or wheelchair is eroticized. He concluded that people seek amputation to attain sexual fulfillment.

Amorous yearnings do seem to play a role in many cases of BIID. In 1997 Richard L. Bruno, a specialist in brain-body disorders at the Englewood Hospital and Medical Center in New Jersey, described a subset of BIID patients who are sexually attracted to amputees and are thrilled by the idea of being an amputee; he dubbed such people "devotees." And psychiatrist Michael B. First of Columbia University reported in a 2004 paper that nearly 90 percent of 52 people with BIID felt sexually drawn to amputees.

But sexual urges do not fully explain the disorder. In First's study, only 15 percent of the subjects he interviewed said that sexual excitement was the primary reason for wanting to be an amputee. Similarly, Bruno identified a number of people whose desire for an amputation was not primarily driven by erotic fantasies but rather by disability itself. People he called "wannabes" yearn to become disabled, whereas another group, the "pretenders," seeks to simulate physical disability by, say, wrapping bandages around a limb and using a wheelchair or crutches.

Such people, Bruno argues, are looking for recognition and sympathy more than sexual gratification. He theorized that many of the afflicted lacked attention and love in childhood--when the disorder typically originates--and are looking to get these emotional supports through disability and dependency on others. In support of this theory, Bruno found that some pretenders came from households they described as cold, rigid and asexual. Many reported that as children they felt jealous of the attention received by people in wheelchairs and fantasizing, sometimes obsessively, about being cared for while disabled.

But other researchers characterize the disorder less as a desire for disability than as an anatomical identity crisis. In First's survey, almost two thirds of the subjects said they wanted an amputation primarily to establish their "true identity." For instance, one subject said, "I felt like I was in the wrong body--that I am only complete with both my arm and leg off on the right side."

First likens BIID to gender identity disorder, in which patients are similarly uncomfortable with part of their anatomy because it is at odds with their internal sense of self. Both BIID and gender identity disorder typically originate early in life and are sometimes successfully resolved with surgery. Such similarities suggest, according to First, that BIID is an identity disorder and should be classified as such in the Diagnostic and Statistical Manual of Mental Disorders (DSM), the standard handbook for mental health professionals.

Perturbed Body Maps
Such an identity crisis most likely has a neurological basis. Some researchers theorize that the disorder results from a distortion or deletion in one of the maplike representations of the body in the cerebral cortex, the brain's outermost layer [see box on preceding page]. For instance, brain damage might injure the neurons that create a piece of this body image, leading to a sense that a part of the body does not belong. Thus, a person might want to get rid of that part so that the body conforms to its representation in the brain.

Because brain damage would likely affect one particular spot in the map, such an injury or aberration could account for the fact that BIID patients typically want to rid themselves of a specific limb in a precise location. One of First's subjects, for example, wanted to cut off both legs above the knees, and that well-defined desire persisted even after he had his left arm amputated above the elbow after a shotgun accident. In fact, most of those in First's study who yearned for a leg amputation specified that they wanted it to occur above the knee.

What is more, body-image distortions are known to result from tumors or strokes in the parietal lobe, which contains a body map that is derived from sensory inputs. In a case described by British neurologist Oliver Sacks in his 1984 book A Leg to Stand On (Summit Books), a young man woke up to discover that someone else's leg was in bed with him; the man assumed it was from a corpse. But when he tried to throw it out of the bed, he landed on the floor himself. The leg was attached to him, but it seemed to be a counterfeit of his own, which had somehow vanished.

Physicians discovered a tumor above the patient's right parietal lobe that had begun to bleed during the night. Sacks posited that the tumor was corrupting his brain's body map. Once the tumor was removed, the man regained a normal impression of his physique.

Likening BIID to such cases of somatoparaphrenia, in which patients deny that a part of their body is theirs, neuroscientists Vilayanur S. Ramachandran and Paul McGeoch of the University of California, San Diego, suggested in a 2007 paper that parts of the parietal lobe might also be damaged in BIID patients. Such an insult could presumably decouple a specific part of the body from the body map in that lobe.

In other instances, BIID might result from a peripheral injury. In 1974 Sacks severely injured his left thigh in an encounter with a bull in the mountains of Norway. After the wound healed, he felt no connection to his thigh and occasionally wished to have the leg amputated. Amputation, he wrote in A Leg to Stand On, would "relieve me of having to drag around a totally useless, functionless, and indeed 'defunct' limb." Sacks theorized that such bodily harm might in some circumstances interrupt communication between the limb and the brain.

Some BIID patients similarly recall childhood injuries involving the limb that they shortly thereafter became obsessed with amputating. In about one fifth of the subjects in First's 2004 study, a disability such as a limp or broken leg provided the impetus for their desire for an amputation. But many cases of BIID could stem from congenital aberrations in neural pathways, with injuries or other environmental factors playing a secondary role.

Curbing the Hunger
Traditional psychotherapy and medication, such as antidepressants, have so far had little effect on the desire for amputation. For instance, neither technique had much influence on BIID symptoms in the subjects in First's study who had tried it. In hopes of finding a more effective treatment, researchers are investigating ways to target the neurological underpinnings of BIID.

Sacks helped many of his patients with movement therapy, in which a therapist guides a patient through coordinated sequences requiring the use of the affected body part. Such therapy is thought to reintegrate the estranged body part with its representation in the brain. Sacks believes that a violin concerto by Mendelssohn helped to reincorporate his own leg into his body's neuromuscular walking program after his accident. "The leg came back" to the rhythm and melody of the music, the neurologist wrote.

Such simple cures may work to reinvigorate atrophied neural connections between body and brain. They may not be effective, however, if the foreign part of the body has actually been deleted from the brain's body map. A method under investigation by Ramachandran and McGeoch might work better in such instances. Rinsing an ear canal with warm and then cold water, which stimulates the half of the brain opposite the treated ear, temporarily alleviated somatoparaphrenia in stroke patients. The technique may work by exciting the parietal lobe, and the researchers now want to test it on people with BIID. If the method helps such patients, doctors might try the more lasting tactic of implanting electrodes that zap the relevant brain region directly.

Currently the most effective treatment for BIID may be the most damaging: surgery. The six patients in First's survey who had received an amputation at their desired location reported that the procedure abolished their yearning to cut off a limb and brought them great happiness. "Since I had it done five years ago," one person said of an amputation, "I've felt the best I've ever felt." Another remarked, "It finally put me at peace. I no longer have that constant, gnawing frustration."