Selective impairment in the retrieval of family relationships in person identification: a case study of delusional misidentification.

We describe a 74-year-old, right-handed woman who exhibited a peculiar form of delusional misidentification due to Alzheimer's disease (AD) combined with idiopathic normal pressure hydrocephalus (iNPH). The patient's most distinctive symptom was that she often misidentified her daughters as her sisters. She had severe atrophy of the bilateral medial temporal lobe and right-hemisphere-dominant hypoperfusion in the fronto-temporo-parietal cortices. Detailed tests revealed that she had a selective deficit in retrieving the family relationships between herself and her daughters/husband (i.e., she misidentified her daughters as her sisters and her husband as her father), despite being able to retrieve the names and faces of her family members, and some person-specific semantic information (e.g., occupation) related to them. We speculate that this specific type of misidentification can be elicited by failure to update semantic memory through the encoding of new episodic memory due to right-hemisphere-dominant fronto-temporal dysfunction.