Clinical and Neuroimaging Features of Tactile Hallucinations in Patients With Dementia With Lewy Bodies: A Cross-Sectional Study.

Background: We examined the clinical features of tactile hallucinations associated with dementia with Lewy bodies and investigated their neural substrates.

Methods: This retrospective observational cross-sectional study enrolled 147 patients with probable dementia with Lewy bodies from the Department of Psychiatry, The University of Osaka Hospital, and collected the data of Clinical Dementia Rating, Mini-Mental State Examination, Neuropsychiatric Inventory-plus, and their demographics. Furthermore, magnetic resonance imaging and cerebral blood flow data from single-photon emission computed tomography were collected when possible.

Results: Ten patients (6.9%) had tactile hallucinations. There were no significant differences in age, sex, or cognitive function between the patients with and without tactile hallucinations. The patients with tactile hallucinations had more severe neuropsychiatric symptoms, although none developed delusional infestations. Magnetic resonance imaging showed lower grey matter volume in the right postcentral gyrus, and single-photon emission computed tomography images showed lower cerebral blood flow in the left postcentral gyrus and relatively higher cerebral blood flow in the left inferior frontal gyrus in patients with tactile hallucinations than in those without. Single-photon emission computed tomography was available for only three patients among those with tactile hallucinations. Cerebral blood flow in the postcentral gyrus was reduced in all three patients compared with the database of age-sex-matched healthy controls.

Conclusions: These findings suggest that tactile hallucinations in patients with dementia with Lewy bodies may be related to damage in the postcentral gyrus and preserved function in the frontal lobe; this could be consistent with the "release phenomena" hypothesis of hallucinations.