In BIID, or apotemnophilia, individuals express a strong desire to have a healthy limb amputated at a very specific location. People with this condition usually describe the affected limb as being “intrusive” or “over-present”, and report that they have had the desire to remove since early childhood, but do not understand why. This desire can be so strong that sufferers sometimes resort to damaging the affecting limb irreparably, thus forcing doctors to amputate it. The vast majority of BIID sufferers have no other psychological disturbances, and almost always say that they feel much happier when the limb is eventually amputated.
A growing body of literature suggests that body awareness disorders such as BIID occur as a result of abnormal activity in the right parietal lobe, which is known to be essential for constructing a mental representation of the body. Specifically, this body image is constructed in the superior parietal lobule (SPL), which performs a function referred to as multisensory integration, whereby different types of sensory information entering the brain are brought together. Thus, information from the visual parts of the brain and the primary somatosensory cortex, which processes tactile sensations and proprioceptive information relating to the position of the body within space, is sent to the superior parietal lobule. There, it is combined with information from the motor cortex, which controls movement, and all is processed further to generate an internal model of the body. If these processes are perturbed, the body image is compromised.