It鈥檚 a bizarre and rare disorder, but its consequences can be horrific. One man with (BIID) dumped his lower leg in dry ice for several hours until doctors were forced to amputate. Others have resorted to wood chippers and gunshots to do away with healthy limbs they never wanted.
Now a study of four men with BIID suggest their condition is linked to reduced activity in a brain area involved in forming a mental body map.
鈥淭hey can feel the body being touched, but it does not integrate into their sense of body image,鈥� says , a neuroscientist at the University of California, San Diego, who presented the study at a recent in Frankfurt-am-Main, Germany.
Advertisement
鈥淭hey know the limb is part of their body, but it鈥檚 鈥榤ore鈥� than it should be. It should be gone,鈥� he adds.
Sexual oddity
The disorder, also known as apotemnophilia, was first described in 1977 by the American sexologist John Money. He classified it as an intense sexual desire to have an amputation, hence its original name, which is Greek for love of amputation.
Most patients, however, don鈥檛 describe their desire to be amputees as sexual, says , a psychiatrist at Columbia University in New York who has conducted extensive interviews with dozens of patients.
鈥淚t鈥檚 very, very rare,鈥� First says of all forms of the disorder. 鈥淚鈥檝e been working on this condition now, researching it for 8 years, and I almost never get calls from therapists saying 鈥業 have somebody with this. I need your advice.鈥� 鈥�
Brain malfunction
Explanations for how BIID develops have run the gamut, from a cry for attention to early childhood exposure to an amputee, McGeoch notes. Those explanations 鈥渟eemed absolute nonsense to us鈥�, he says.
Instead, he and co-author David Brang theorise that the disorder is caused by a malfunction in a brain area called the right parietal lobe. Other studies have linked this region to people鈥檚 representation of their own body: stroke patients who suffer damage to this area sometimes fail to recognise a limb as their own.
鈥淲e suggest that perhaps apotemnophillia, or BIID or whatever you want to call it, is a cognitive variation on this 鈥� there鈥檚 something cognitively wrong with their right parietal lobe,鈥� McGeoch says.
To test this hypothesis, McGoech鈥檚 team recruited four men with BIID via internet support groups. Though precise numbers are hard to come by, the disorder is about 10 times more common in men than in women.
Scanning evidence
The team tested subjects using a non-invasive brain imaging technology called magnetoencephalography (MEG), which measures the tiny magnetic fields created when neurons fire.
When researchers touched the limb that BIID subjects perceived as normal, their right parietal lobe kicked into action. When they touched the limb subjects wanted gone, activity in the right parietal lobe didn鈥檛 change.
One patient who wanted both his legs amputated registered no increased activity at all, McGeoch鈥檚 team found. Meanwhile, four volunteers with no desire to hack off a limb cranked up their right parietal lobes when researchers touched either leg.
鈥淭he fact that they鈥檙e able to scan anybody is amazing,鈥� given the rarity of BIID, says First. He guesses that no more than a few thousand people worldwide have the disorder.
Warped body image
He is, however, not yet convinced that a deficit in the right parietal lobe causes BIID. It鈥檚 also possible that a strong desire to amputate a limb could transform neural circuitry in a brain region responsible for body image, he says. 鈥淭here鈥檚 a chicken-and-egg problem here.鈥�
The limb that patients want amputated can change throughout their lifetime, First notes. 鈥淭hat can鈥檛 be explained by a cognitive mismapping [of the limb].鈥�
Deeper insight into the causes of BIID could offer insight into how to treat the condition. Drugs that alleviate symptoms of obsessive compulsive disorders are one possibility worth testing, First says.
Yet many patients see an actual amputation as the best treatment possible. 鈥淚 have never heard of them regretting it,鈥� McGeoch says. 鈥淭hey鈥檙e always delighted.鈥�
Journal reference:
