A fifty year-old man was admitted through the emergency room with extensive dry ice injuries to his left leg. For two days his doctors tried to save the leg, but the damage was too extensive so eventually they had to perform a below-knee amputation. During this time the patient also suffered from small strokes due to fat emboli from the damaged leg.
After the surgery the patient recovered well. He told his doctors that the dry ice injuries were deliberate and that the amputation was the outcome he was hoping for. In fact he was coached throughout the process by people in an online forum, who helped him determine when the damage was extensive enough that amputation would be required.
The initial reaction to such a case is often that this person must be suffering from a kind of mental illness. Perhaps he is psychotic, or this is an extreme version of Munchausen syndrome where people inflict harm on themselves for psychological reasons. This is not the case, but this is similar to the process that the medical profession went through when first encountering these rare cases.
This condition is now known as Body Integrity Dysphoria (BID), previously Body Integrity Disorder or Body Integrity Identity Disorder. But BID was previously described by two psychologists in 1977 in the Journal of Sex Research, in which they named it apotemnophilia. They thought BID was primarily a paraphilia, in which subjects were erotically stimulated by amputations and the thought of themselves being an amputee.
The earliest possible described case, however, goes back to 1785 – French surgeon Jean-Joseph Sue reported a case of a man who paid him to amputate a healthy leg, forcing him to do it at gunpoint, but later reported that this fulfilled his life-long wish. Cases of apparent BID were also described in the 1906 book Pscyopathia Sexualis.
Our understanding of BID has followed a familiar pattern of many complex neurological conditions, first thought to be psychological. This is similar to the once popular theory that autism was caused by a lack of warmth from parents, the so-called “refrigerator mother” theory. We see this today with popular theories regarding gender dysphoria.
This mistake stems in part from that fact that many people do not understand that our experience and sense of self is not a passive result of reality but an active and constructive neurological process. What I mean by this is that you do not feel that you exist inside your body, that you are your body, that you are separate from the rest of the universe, that you own the parts of your body, and control those body part simply because you do. You have these sensations because there are circuits and networks in your brain that actively construct those sensations. We partly know this from cases where these networks fail or are suppressed, resulting in out-of-body experiences, or conditions such as alien-hand syndrome.
There are also cases where the internal body map in the brain does not align with the body itself – phantom limb pain syndrome. In such cases a body part is amputated but the corresponding brain map is still functioning, creating the illusion that the missing limb is still there. There are even cases where patients, after suffering a stroke, experience a supernumerary phantom limb, the sensation that they have an extra limb. Again – this is not a delusion. These patients are not mentally ill. They report a sensation that is at odds with physical reality.
Understanding of phenomena like alien-hand and phantom limb lead to the hypothesis that perhaps BID is also a mismatch between the brain’s internal body map and the body, in this case the offending limb may simply be missing from that map. That would cause the person to feel as if the body part does not belong to them, which can cause distress (dysphoria). They feel they are “overcomplete”, and that they would feel more natural without the body part. These sensations are often recognized from very young (often by age 5), and are persistent throughout their life.
BID was mistaken for a paraphilia likely because many people with BID feel really good when they imagine themselves without the body part they feel does not belong to them, or when they see someone missing that same body part. The relief of the persistent dysphoria can cause a type of euphoria that is some people with BID can cause secondary sexual arousal. This appears to be an epiphenomenon, not what is driving the BID sensations. In the case report above, the subject did not report any associated sexual arousal.
What happens when we turn our modern imaging tools on the brains of those with BID? We can image anatomy and even map connectivity in the brain. What we find aligns well with what we might expect to find. The first relevant study comes from 2011, Xenomelia: a new right parietal lobe syndrome. They studies four subjects with BID using magnetoencephalography while stimulating the unwanted limb and other parts of the body. In all cases the sensation caused the typical response in the sensory parts of the brain. However, only when touching the unwanted body part, the expected activation in the right superior parietal lobule (rSPL) was not activated. What does this mean?
Sensory input in the brain is hierarchical. It begins with primary sensory areas, which then feed to progressively higher brain areas that do more sophisticated processing and incorporate the sensory input into cognitive and emotional processes. The rSPL appears to be involved in incorporating various sensory inputs into a coherent sensation of the whole body. Those networks I discussed above that actively create the sensation of self rely heavily on sensory input. In cases of BID sensations from the unwanted limb do not appear to be incorporated into the body map at higher levels.
A 2013 fMRI study found a similar decrease in activity in the ventral premotor cortex. A 2017 connectivity study found hyperconnectivity in somatosensory areas in subjects with BID. This study suggests that BID may be more complex than a simple mismatch in the body’s internal map and, at least in some cases, may reflect a broader dysfunction in the networks that create the sense of self.
An important 2020 study also focused on the rSPL. They found that this area was atrophied and had hypoconnectivity in subjects with BID. Further, they found that the more intense the feelings of BID the greater the degree of atrophy, which is strong evidence for an actual cause and effect. Many of these findings have been replicated in recent years.
Finally there is a 2025 study that found that sensory activation of the unwanted limb created increased activation of brain centers associated with sensory arousal, pain and reward. These are likely the neuroanatomical correlates of the dysphoria part of BID – the unwanted limb activates distress signals in the brain because it detects that there is something wrong.
To summarize, BID is associated with a mismatch in the internal model of self and the body itself, with general altered function in the networks that generate the sense of self and incorporate sensation into this model, and activation of internal stress due to the mismatch. Clinically BID behaves like a neurological disorder – young onset and lifelong persistence. And now we have the neuroanatomical correlates to back this up.
Further, BID does not respond to talk therapy. Therapy may help with dealing with some of the effects of BID, but does nothing to resolve the BID itself. Medication is likewise ineffective. This leads to a hotly debated ethical dilemma – is it medically ethical to amputate a healthy body part as a treatment for BID? Outcomes do appear to be good, and not taking corrective action often leads to self injury and seeking non-medical amputation. Understanding the neuroscience of BID at the very least can help inform this difficult debate.
The neuroscience of BID is good to keep in mind when considering other conditions that may superficially seem purely psychological. Obviously, there are psychological and psychiatric conditions. I am not saying they don’t exist. It is curious, however, that we (individually and collectively) often assume a psychological cause, even in conditions that are ultimately understood as purely neurological. I suspect this is because it is difficult to think of the core aspects of our sense of reality and sense of self as being constructed by brain networks, rather than a simple recognition of reality. The construction (some might call it an illusion) that our brains create is so compelling we have a hard time recognizing it as a construction.
