Mirrored-self misidentification

Mirrored-self misidentification is the delusional belief that one's reflection in a mirror is some other person (often believed to be someone who is following one around). Often people who suffer from this delusion are not delusional about anything else. It is considered a monothematic delusion; it is sometimes labeled a delusional misidentification syndrome. The disorder is often found within the context of dementia and can also be caused by the organic dysfunction resulting from traumatic brain injury, stroke, or neurological illness.

Causes
Like other monothematic delusions, mirrored-self misidentification is currently thought to be initially caused by a neurological defect, typically in the right hemisphere, which affects one's experience. Current research points to a potential dysfunction that may lead to this disorder:
 * Patients who have impaired face perception (i.e. prosopagnosia) and thus can no longer recognize themselves (similar to Capgras delusion)