Bipolar disorder (BD) is a chronic and cyclical illness that affects a significant portion of the population, representing more than 1% worldwide. It is characterized by alternating episodes of elevated mood and energy (mania or hypomania) and episodes of decreased mood and energy (depression). These mood episodes manifest as substantial variations in energy levels and behavior, which recur over time and have a major social and occupational impact. According to the World Health Organization, BD rank as the fourth leading cause of morbidity and mortality.
Manic episodes are marked by hyperactivity, exalted mood, insomnia, inflated self-esteem, expansive speech and behavior, and sometimes psychotic symptoms (such as delusions of persecution or hallucinations). In contrast, depressive episodes are characterized by low energy, sadness, social withdrawal, hypersomnia or insomnia, and low self-esteem, often accompanied by weight loss or gain and decreased or increased appetite. The risks associated with manic, depressive, or mixed episodes are numerous; notably, individuals with BD have a suicide rate up to 20 times higher than that of the general population. Nearly half of patients with BD will attempt suicide at least once in their lifetime, and 15-20% of these attempts are fatal.
BD are associated with a marked reduction in quality of life, often greater than that observed in other mood or anxiety disorders. This decrease in quality of life is more strongly correlated with depressive symptoms than with manic or hypomanic symptoms. Furthermore, poor quality of life is related to residual depressive symptoms that may persist during remission periods, as well as to the high comorbidity of bipolar disorder with anxiety disorders.
The annual relapse rate ranges between 40% and 61% during the first two years following the initiation of treatment. This high incidence of relapse makes stabilization particularly difficult for patients with BD, with a period of significant vulnerability following each episode. The average duration of hospitalization is 58 days, at an approximate cost of €850 per day, resulting in direct hospitalization costs related to mood disorder relapses of about €3 billion per year. According to the French Court of Auditors, for every euro of direct cost, there are two euros of indirect costs related to social benefits and the negative impact on employment. Extrapolating these figures, the cost of hospitalizations due to relapses in BD is estimated at €45 billion across Europe.
Moreover, each relapse or rehospitalization irreversibly affects the individual's cognitive functioning and contributes to social and occupational disintegration. Staging models of the illness based on neuroprogression have been developed, taking into account the number of relapses and the degree of functional impairment. However, these models are not yet implemented in clinical practice.
Preventing (hypo)manic and depressive episodes through early intervention is therefore a key priority both at the individual level and as a major public health issue.
A new line of research has emerged in mood disorders, focusing on the digital phenotype. Among new digital biomarkers of relapse, voice appears to be a promising parameter. Several studies have demonstrated the efficacy of automated speech analysis, using machine learning models, to aid in the diagnosis of psychiatric disorders. In bipolar disorder, the illness has been shown to influence patients' vocal and linguistic features.
Thus, the main hypothesis of the study is that automated speech analysis and lifestyle data can be used to develop a model capable of predicting either relapse (manic, depressive, or mixed episode) or the transition to a high-risk state in patients with bipolar disorder.
