A vestibular biomarker of manic and depressive phase in bipolar disorder

Background and objectives: Bipolar disorder (BD) is a neuropsychiatric disorder characterized by cyclic changes in mood between hypoactive, pessimistic (depressive phase) and hyperactive, optimistic (manic/hypomanic phase). Prior studies in major depression patients show that the right side of the vestibular system (inner ear's equilibrium system) is less active compared to the left. It suggests a relationship between mood and abnormal lateralization of the vestibular activity. This exploratory investigation analyzes the right and left vestibular activity in different mood phases of BD and healthy controls. Design: A transversal cross-sectional study. Methods: We will study and compare the lateralization of the vestibular activity of BD I or II patients, who match the selection criteria for different mood phases: depression, mania/hypomania, euthymia and healthy controls (6 patients each group). Outcome measures: For vestibular evaluation, we will use rotary chair technique and electronystagmography. The primary outcome measure is the per- and post-rotatory asymmetry. The secondary outcome measures are the slow phase velocity of the nystagmus, the rhythmicity of nystagmus, and the type of slow ocular tracking. Discussion: This study addresses the relationship between mood states and abnormal right-left side lateralization of the vestibular activity in BD patients. Ethics and dissemination: The study protocol was approved by the ethics committee of Servicio de Salud Metropolitano Oriente, in Santiago, Chile on June 21st, 2016. Participants will provide written informed consent prior to participation in the trial. Trial registration: ClinicalTrials.gov identifier: NCT02827045 on July 6th, 2016.