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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. Asomatognosic patients may, for example, mistake their arm for the doctor’s arm, however, can be shown their limb and this error is temporarily 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 or not 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.
Somatoparaphrenia in popular culture
In the fourth episode of the first season of the short-lived medical drama 3 lbs, a veteran who has suffered a stroke claims his left arm belongs to another soldier, who died. On the show, the condition is misdiagnosed as anosognosia, denial of one's sickness.
In the fifth episode of the fourth season of Grey's Anatomy, a man suffering from somatoparaphrenia, misdiagnosed as body dysmorphic disorder, wants the doctors to amputate his foot because it does not belong to him.
In episode ten, "In Case of Co-Dependents", of the first season of A Gifted Man, one of the main characters, Anton, becomes afflicted with somatoparaphrenia after suffering from a gunshot. The limb in question was his left arm. His delusion is cured through cold water irrigation in his left ear.
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