Wait, Whose Leg Is That?

A previously healthy young man wakes into a thought-paralyzing panic when he finds a leg in bed with him. There’s not a person whose leg he notices first, there’s just a leg. He frantically tries to throw the leg anywhere that’s not in bed with him and finds himself lying on the ground, staring at a foreign limb which has replaced his own. After what I’m sure was a surreal and terrifying trip to the hospital, a large tumor was found in his brain, resected, and the sense of ownership of his limb returned. Decades ago in an entirely different case, Dr. Oliver Sacks was hiking alone on a remote mountain in Norway (don’t hike alone on remote mountains in Norway). After a series of unfortunate but entirely foreseeable events, he was left with a severely broken leg. From that point on, Dr. Sacks often felt a sense of alienation from his limb. Not a paralysis or lack of sensation, but the deep and pervasive belief that his leg was not his own, physically attached but completely absent from his sense of self. He went on to publish A Leg to Stand On, a uniquely personal clinical look on a rare condition dubbed Body Integrity Identity Disorder (BIID).

Like most neurological conditions which present with only internalized mental symptoms, there’s a significant amount of debate concerning the possible causes, diagnosis, and treatment of this disease. In some cases, patients will present with requests for limb amputation which appear to arise from apotemnophilia, or sexual arousal tied to the image of oneself as an amputee. Other times this request stems from a childhood bereft of attention or love which causes the sympathy directed toward the injured, sick, or handicapped to be intensely desirable. These situations are incredibly complex and infuriatingly sad, so I’ll stick to examples more neurological than psychological in nature.

Wait, Whose Leg Is That?

That weird looking fella up there is known as a homunculus. It’s a representation of the primary somatosensory cortex of the brain, the region containing neurons and tracts relating to tactile sensation (pressure, two-point discrimination), proprioception (location in space), and some visual input. The visual cortex is in another region of the brain but the pathways interact and the final, consciously-assembled “sense of self” takes input from all of the above. The size of the various body regions depict disparities in how much of our brain we devote to various regions and the ensuing increases in fine sensory discrimination. Unsurprisingly your face, mouth, hands, feet, and sexual organs receive more attention than expected based on size alone (that’s the dick joke if you’re keeping track). Even something as simple as catching a ball requires all of these working together. Your visual system has to identify the ball in flight and predict the path the ball will follow, your somatosensory and motor systems must then identify where your arm is in space, move your arm and hand to the expected arrival location of the ball, and then help time the fine motor movements involved in actually grasping the ball in flight. This is also an example of why the “five senses” don’t encompass all of our faculties. There are sensory cells in every muscle and joint in your body, and the collected signals from your biceps, triceps, pecs, etc tell your brain where your arm is, relative to your body, even devoid of vision and with an entirely numb limb.

This sensory model is usage dependent. If a limb is paralyzed and numbed for an extended period of time, the region of the brain responsible for it can gradually be adopted by neighboring areas. Rehabilitation through the repeated use of this limb can return function and effectively rewire that region of the brain to once again relate to the original limb. Of course, things don’t always go so smoothly, it’s no fun writing about when everything goes smoothly.

This homunculus can give a rough explanation for the phantom limb pain that amputees sometimes experience. The sensory region of the brain can remain active and continue to be self-identified as representing the now absent limb. However, in BIID, a region of this map can be “blank” or “miswired” to some degree. The patient can retain control and sensation of the limb, but that limb will not be correctly identified as self. It’s a bizarre condition to try and describe or understand. For the young man above, the brain tumor bled overnight into the parietal lobe of his brain, and the leg region of the homunculus was impaired. This alienation is more than a slight nuisance, and often causes emotional disruptions with severe negative impacts on social, professional, and personal relationships. The condition usually presents in childhood, and while it can be related to a physical injury, doesn’t appear to require a specific trigger. In severe cases, these patients will request amputation of the limb, stating that they feel “over complete.” When denied, patients have gone so far as attempts of self-amputation or injuring their limb to an extent which requires amputation (shooting, freezing, crushing, etc). Dr. Sacks, mentioned above, stated amputation would “relieve me of having to drag around a totally useless, functionless, and indeed ‘defunct’ limb.” It should be noted his leg wasn’t functionless and he could walk without dragging it (full disclosure: Dr. Sacks appears to have garnered some of his material and inspiration as a physician-writer through self-designed and implemented “experiments” which involved taking copious amounts of mind-altering recreational drugs and seeing what happened). That being said, the condition in question here was well documented before his experiences and certainly exists beyond the amphetamine and LSD prone Dr. Sacks (see also: Francis Crick, James Watson, and Dock Ellis).

Wait, Whose Leg Is That?

This situation raises some dicey ethical questions. Imagine you’re a surgeon with a patient in front of you. They’ve held a lifelong belief that their leg should stop two inches below the knee (an interesting side effect of the faulty somatosensory cortex is a clearly defined line where “self” and “alien” meet). Furthermore, the patient is depressed, suicidal and threatening self-harm if denied amputation.

Patient autonomy is often a trump card of medical ethics. If a patient consistently desires this amputation, understands the risks and effects of such a procedure, and is not psychotic, it’s a commonly held belief that elective amputations are ethically permissible. Obviously, this doesn’t mean the amputation is medically warranted or advised.

There have been instances of surgeons going through with these amputations, often with positive results and patients reporting relief of symptoms and improvement of quality of life. There’s not many last-ditch treatment efforts more extreme then “let’s cut off that leg and see if you feel better” but given the complexities and extreme rarity of BIID, alternative treatment methods are largely unverified and have questionable efficacy.

Oddly enough, increased understanding and advanced treatment of this condition may arise due to warfare trauma medicine. Improvements in treating severe trauma have led to decreased mortality rates and increased amputation rates. The growing patient population has helped drive attention, funding, and research to phantom limb treatment. The eventual greater understanding of cause and treatment efficacy of phantom limb pain will likely involve manipulation of the same somatosensory cortex responsible for BIID.