The condition, called the Fregoli delusion, is named after the Italian actor Leopoldo Fregoli who was renowned for his ability to make quick changes of appearance during his stage act. It may result from brain lesions, antiparkinsonian medication, or other causes.
A person with the Fregoli delusion can also inaccurately recall places, objects, and events. This disorder can be explained by "associative nodes". The associative nodes serve as a biological link of information about other people with a particular familiar face (to the patient). This means that for any face that is similar to a recognizable face to the patient, the patient will recall that face as the person they know.
It's a specific delusional misidentification syndrome.