A 60 year old man is brought to a psychiatrist with a 10 year history, that he suspects his neighbours and he feels that whenever he passes by they sneeze and plan against behind his back. He feels that his wife has been replaced by a double and calls the police for help. He is quite well groomed alert, occasionally consumes alcohol, likely diagnosis is-

This patient has:- Delusion of persecution (suspects his neighbours sneeze and plan against him). Delusion of double (wife has been replaced by double). No impairment in consciousness (patient is well alert) Symptoms for 10 years. Delusion of double is a bizarre delusion (i.e., belief which is impossible in reality). If delusion is bizarre, only one criteria is required for diagnosis. About other options Delusions are a feature of psychosis, and amongst the given disorder only schizophrenia is a typical example of schizophrenia. Alcohol withdrawal can also cause psychotic symptoms, but it can be excluded because:- In alcohol, withdrawal patient is not well alert (impaired consciousness) Alcohol withdrawal is rare with occasional consumption Symptoms will not persist for 10 years Paranoid personality and conversion disorder are not psychosis → No delusion.