Some people are seized with a desire to cut off their own limbs, which they somehow feel are not really part of their body. An attempt to treat them using indirect brain stimulation has failed, but could help explain what lies at the root of this strange disorder.

People with body integrity identity disorder (BIID), or xenomelia, say that some part of their body – usually a limb – doesn’t belong to them. They often resort to desperate measures such as freezing the limb in dry ice to force doctors to amputate it.

Bigna Lenggenhager of the University Hospital Zurich in Switzerland and colleagues sought to treat the condition by targeting part of the system that gives us a sense of awareness of our body. They used a technique called caloric vestibular stimulation (CVS), involving pouring cold water into the ear canal. The flow of water induces an illusion of motion, and is thought to stimulate regions of the brain that create a mental map of the body. These regions integrate external senses such as touch with internal sensations, including those from the vestibular system, which helps us balance.

Previous work had showed that CVS can temporarily relieve the effects of a condition called somatoparaphrenia, where people deny ownership of a paralysed limb. But when Lenggenhager’s team tested the technique on 13 people with BIID, they found no such effect.


Durable desire

“Obviously the desire to amputate is much more durable than these other disorders of body image [such as somatoparaphrenia],” says Paul McGeoch at the University of California, San Diego, who was not involved in the new work.

What makes BIID so intractable? Neurological differences may be implicated. Previous studies have shown people with BIID have a thinner cortex in brain areas involved in integrating different types of sensations to root us in our bodies.

Brain scans of five people with BIID also showed they had less activity in parts of the prefrontal cortex when their alienated limb was stimulated compared with other limbs. This brain area is thought to be crucial for our sense of body ownership.

Even if adult BIID patients show such neurological changes, it is possible that long-standing behaviours could eventually lead to the neurological changes seen. For instance, people with BIID can ignore their offending limb for decades, by sometimes strapping it and walking on crutches or sitting in wheelchairs. “This might also affect how the body is represented in the brain,” says Lenggenhager.

If BIID really is neurological, the next step would be to pinpoint the exact brain areas affected. “I think it could be relevant for therapies,” says Lenggenhager.

Journal reference: Cortex, DOI: 10.1016/j.cortex.2014.02.004