Delusions of substitution and diabetes mellitus.

A male patient with chronic paranoid schizophrenia developed delusions of substitution that were of abrupt onset and short duration. This coincided with the detection of diabetes mellitus. Over the next three years, despite being on continuous moderate dose neuroleptic treatment the re-emergence and resolution of delusions of substitution varied with the control of his diabetic status. A selective review of reports on organic contributors to delusions of substitution is presented. It is suggested that the abruptly appearing, short lasting delusions of substitution may be more likely to have a known organic contributor.