On the distinction between monothematic and polythematic delusions

Some delusional patients exhibit only a single delusional belief (or several delusional beliefs concerning a single theme): this is monothematic delusion. It contrasts with polythematic delusion, where the patient exhibits a variety of delusions concerning a variety of different themes. The neuropsychological bases of various monothematic delusions are rather well understood, and there is a well-worked-out general neuropsychological theory of monothematic delusion, the two-factor theory. Whether polythematic delusion might be explained in a similar way is an open question: I sketch some possible ways in which a comparable two-factor account might be developed for polythematic ('psychiatric') delusional conditions such as delusions of reference.