A patient with delusional infestation by proxy: Issues for vulnerable adults

A 57-year-old Caucasian female presented to our clinic with her 23-year-old son, who was profoundly autistic. Our patient was convinced that her son had an infestation with fibers and believed that he had developed the condition as a young child. She described the symptoms of the infestation in her son's skin on his behalf, as he was not able to communicate. She identified dietary factors as a causative factor and wanted them removed from his diet. Her son had seborrhoeic dermatitis on examination, with no evidence of an infestation. Our patient later identified that fibers were coming out of her skin also. Her medical history included a road traffic accident resulting in back pain. Blood, urine, and microbiological investigations were normal. She was diagnosed with delusional infestation (DI) by proxy, and was started on risperidone. We present an interesting case of a patient with DI by proxy, in which the delusional beliefs of the mother have been projected onto her son. Issues of safeguarding vulnerable adults are raised in such cases, suggesting the crucial role of the physician in ensuring patient safety. DI by proxy has been reported in patients with children and animals, but we believe this is the first report of DI by proxy involving a vulnerable adult.