Somatoparaphrenia is a type of monothematic delusion where one denies ownership of a limb or an entire side of one's body. Even if provided with undeniable proof that the limb belongs to and is attached to their own body, the patient produces elaborate confabulations about whose limb it really is, or how the limb ended up on their body. In some cases, delusions become so elaborate that a limb may be treated and cared for as if it were a separate being.
Somatoparaphrenia differs from a similar disorder, asomatognosia, which is characterized as loss of recognition of half of the body or a limb, possibly due to paralysis or unilateral neglect. For example, asomatognosic patients may mistake their arm for the doctor’s. However, they can be shown their limb have this mistake corrected.
Somatoparaphrenia has been reported to occur predominately in the left arm of one's body, and it is often accompanied by left-sided paralysis and anosognosia (denial or lack of awareness) of the paralysis. The link between somatoparaphrenia and paralysis has been documented in many clinical cases and the question arises as to whether paralysis, anosognosia or both are necessary for somatoparaphrenia to occur.
It has been suggested that damage to the posterior cerebral regions (temporo-parietal junction) of the cortex may play a significant role in the development of somatoparaphrenia. However, more recent studies have suggested that damage to deep cortical regions such as the posterior insula and subcortical structures such as the basal ganglia may also play a significant role in the development of somatoparaphrenia.
It is believed that this disorder is caused by parietal or biparietal strokes. Somatoparaphrenia has been associated more often with posterior damage of the cerebral regions, specifically the temporoparietal junction, typically seen on the right side.
One form of treatment that has produced a more integrated body awareness is mirror therapy, in which the individual who denies that the affected limb belongs to their body looks into a mirror at the limb. Patients looking into the mirror state that the limb does belong to them; however body ownership of the limb does not remain after the mirror is taken away.