The desire for healthy limb amputation: structural brain correlates and clinical features of xenomelia

Xenomelia is the oppressive feeling that one or more limbs of one's body do not belong to one's self. We present the results of a thorough examination of the characteristics of the disorder in 15 males with a strong desire for amputation of one or both legs. The feeling of estrangement had been present since early childhood and was limited to a precisely demarcated part of the leg in all individuals. Neurological status examination and neuropsychological testing were normal in all participants, and psychiatric evaluation ruled out the presence of a psychotic disorder. In 13 individuals and in 13 pair-matched control participants, magnetic resonance imaging was performed, and surface-based morphometry revealed significant group differences in cortical architecture. In the right hemisphere, participants with xenomelia showed reduced cortical thickness in the superior parietal lobule and reduced cortical surface area in the primary and secondary somatosensory cortices, in the inferior parietal lobule, as well as in the anterior insular cortex. A cluster of increased thickness was located in the central sulcus. In the left hemisphere, affected individuals evinced a larger cortical surface area in the inferior parietal lobule and secondary somatosensory cortex. Although of modest size, these structural correlates of xenomelia appear meaningful when discussed against the background of some key clinical features of the disorder. Thus, the predominantly right-sided cortical abnormalities are in line with a strong bias for left-sided limbs as the target of the amputation desire, evident both in our sample and in previously described populations with xenomelia. We also propose that the higher incidence of lower compared with upper limbs (∼80% according to previous investigations) may explain the erotic connotations typically associated with xenomelia, also in the present sample. These may have their roots in the proximity of primary somatosensory cortex for leg representation, whose surface area was reduced in the participants with xenomelia, with that of the genitals. Alternatively, the spatial adjacency of secondary somatosensory cortex for leg representation and the anterior insula, the latter known to mediate sexual arousal beyond that induced by direct tactile stimulation of the genital area, might play a role. Although the right hemisphere regions of significant neuroarchitectural correlates of xenomelia are part of a network reportedly subserving body ownership, it remains unclear whether the structural alterations are the cause or rather the consequence of the long-standing and pervasive mismatch between body and self.