Delusional Parasitosis as a Presenting Feature of Dementia

A 78-year-old African-American woman first presented to the emergency department with a year’s history of the perception that something was crawling inside her abdomen and rectum. The patient started having this sensation after she was admitted to a hospital for a foot ulcer. While lying on the hospital bed, she felt that something had crawled up her rectum. The patient believed that her abdomen was infested by a parasite, which was eating her insides. The crawling sensation in her rectum was so intense that the patient would sometimes do digital exploration. The patient became upset about these symptoms and went to the emergency department; she was referred to psychiatry after an unremarkable physical examination, including a rectal examination. She did not have any history of drug and alcohol use, and her past psychiatric and family history was unremarkable. There were no symptoms to suggest a mood disorder or delirium. The patient’s head CT scan showed cerebral atrophy and small vessel ischemic changes. Laboratory investigations, including CBC, liver and renal function tests, TSH, B ₁₂, folic acid, and urine analysis, were normal. During the psychiatric evaluation, it was evident that the patient had delusions of parasitosis (somatic delusions) and tactile hallucinations. The patient denied auditory or visual hallucinations or other types of delusions. In addition, she endorsed forgetfulness and scored 6/30 on the Montreal Cognitive Assessment. She had deficits in visuospatial/executive functions, verbal fluency, abstraction, and delayed recall. She was oriented to time, place, and person but not to date, month, or year. The patient’s family corroborated the decline in the patient’s memory, trouble finishing sentences, and declining ability to carry out activities of daily living. The patient was diagnosed with dementia of Alzheimer’s type and psychotic disorder secondary to Alzheimer’s disease according to the DSM-IV-TR. The patient was started on a regimen of risperidone, 0.5 mg/day, and donepezil, 5 mg/day. The dose of risperidone was increased to 2 mg/day over a month, with complete resolution of the patient’s somatic delusions and tactile hallucinations.