How vestibular dysfunction transforms into symptoms of depersonalization and derealization?

Background: Psychiatric Depersonalization/Derealization (DPDR) symptoms were demonstrated in patients with peripheral vestibular disorders. However, only semicircular canals (SCCs) dysfunction was evaluated, therefore, otoliths' contribution to DPDR is unknown. Also, DPDR symptoms in patients with central vestibular dysfunction are presently unknown. DPDR was also studied in the context of spatial disorientation and anxiety, but the relation of these cognitive and emotional functions to vestibular dysfunction requires clarification. Methods: We tested patients with peripheral Bilateral Vestibular Hypofunction (pBVH), Machado Joseph Disease (MJD) with cerebellar and central bilateral vestibular hypofunction, and healthy controls. Participants completed the video Head Impulse Test (vHIT) for SCCs function, cervical Vestibular Evoked Myogenic Potentials test (cVEMPt) for sacculi function, Body Sensation Questionnaire (BSQ) for panic anxiety, Object Perspective-Taking test (OPTt) for spatial orientation and Cox & Swinson DPDR inventory for DPDR symptoms. Results: pBVH patients showed significant SCCs and sacculi dysfunction, spatial disorientation, elevated panic anxiety, and DPDR symptoms. MJD patients showed significant SCCs hypofunction but preserved sacculi function, spatial disorientation but normal levels of panic anxiety and DPDR symptoms. Only pBVH patients demonstrated a positive correlation between the severity of the DPDR and spatial disorientation and panic anxiety. Conclusions: DPDR develops in association with sacculi dysfunction, either with or without SSCs dysfunction. Spatial disorientation and anxiety seem to mediate the transformation of vestibular dysfunction into DPDR symptoms. DPDR does not develop in MJD with central vestibular hypofunction but a normal saccular response. We propose a three-step model that describes the development of DPDR symptoms in vestibular patients.