Delusional misidentification syndrome is an umbrella term, introduced by Christodoulou (in his book The Delusional Misidentification Syndromes, Karger, Basel, 1986) for a group of delusional disorders that occur in the context of mental and neurological illness. They all involve a belief that the identity of a person, object, or place has somehow changed or has been altered. As these delusions typically only concern one particular topic, they also fall under the category called monothematic delusions.

A 67-year-old woman developed a Delusional misidentification syndrome after a right-sided frontally located recurrent convexity meningioma was removed by surgery. After antipsychotic therapy had been established, the patient recovered and the delusions disappeared within a few weeks. A misidentification delusion is a fixed, false belief about the identity of a person, an object, a place, or the time. In the differential diagnosis, psychiatric diseases and neurological diseases are prominent. Patients with a psychiatric disease are usually younger than 40 years, often have a psychiatric history, and usually, have other psychotic symptoms like paranoid delusions and hallucinations. Brain tumors and temporal lobectomy have previously been described as a neurological cause of a misidentification delusion; the surgical removal of a meningioma as such has not been previously described. In patients with a misidentification delusion, the connection between the perception of identity and its accompanying emotions and memories is disturbed. This connection primarily takes place on the right side of the brain, which is in accordance with the location of the removed meningioma in the described patient ¹⁾.