The main finding of our study is the presence of a stable correlation between dissociative symptoms and psychotic features in BD. Moreover, such correlation is related to clinical severity as shown by the higher DES-II total score in patients with a higher number of episodes, aggressive behaviors, seasonality, mixed features, and poor response to mood stabilizers.
Our study is the first to demonstrate that the occurrence of dissociative dimension is higher in BD I, especially in those with psychotic features and in those who present a greater clinical severity (Latalova et al. 2011; Montant et al. 2014; Rafiq et al. 2018).
In our sample, 55% of patients developed psychotic symptoms, and among this group, there were higher levels of dissociative symptoms, combined with a greater psychopathological load and lack response to mood stabilizers (Belteczki et al. 2018). These results could be explained by the fact that dissociative symptoms are more expressed in patients with psychotic symptoms as demonstrated for other mental disorders (Schäfer et al. 2012). According to Allen et al (Allen et al. 1997), who developed the theory of “dissociative detachment”, dissociative phenomena “undermines the individual's grounding in the outer world”, rendering the individual susceptible to developing psychotic features. Moreover, other authors have highlighted the inverse relationship in which dissociation is a defense against the disorganization and acute distress generated by psychosis (Giese et al. 1997). Other possible mechanisms might be the early trauma exposure that predisposes to a higher psychopathological load among different psychiatric disorders, including BD (Carbone et al. 2019; Wang et al. 2021). However, we did not assess the impact of trauma in this study and therefore this explanation remains speculative. Moreover, several clinical variables emerged as strongly associated with the presence of dissociative symptoms. The higher number of lifetime episodes, independently from the episode polarity, is associated with a higher total score. It may be that with the increasing of illness episodes patients’ skills to achieve a functional recovery during the euthymic phases become compromised and, as in advancing age, it correlates with a decrease in cognitive abilities. As to the latter, several studies reported that cognitive dysfunction is associated with a higher number of relapses, a higher number of hospitalizations, dissociative symptomatology, and the worst functional outcome (López-Villarreal et al. 2020). This could partially explain our findings and the association between dissociation and the high number of episodes, but the data available in the literature are still scarce and a more dept analysis of the argument is needed.
Moreover, mixed characteristics are associate with a higher DES-II total score. Mixed features are associated with a lack of response to mood stabilizers in BD and this could explain why patients with dissociative are refractory to treatment. (Swann 2017). Furthermore, mixed features are often triggered by antidepressant therapy, and this feature is also associated with greater dissociative symptomatology as demonstrated by the correlation analysis. Seasonality, in our sample, is associated with dissociative symptoms. This is the first study demonstrating such association. This finding could be explained in the light that a seasonal pattern is associated with a higher number of relapses therefore to worse prognosis (Aguglia et al. 2020; Brandl et al. 2018). Moreover, in our sample, aggressive behaviors are associated with the development of dissociative symptomatology. These behaviors are often related to high levels of impulsivity (Strakowski et al. 2010) and cognitive dysfunction that could explain the higher DES-II scores in patients. The analysis of variance shows that poor response to treatment with mood stabilizers correlates with high DES-II scores. This issue is explainable for two reasons. Patients with worse responses to treatment will experience a worse outcome, a lack of functional and cognitive recovery, and the onset of dissociative symptoms. Secondly, the clinical variables associated with dissociative symptomatology are superimposable with those that predispose to refractoriness to drug treatment.
However, the study also has some important limitations, one being the small sample size. Moreover, the cross-sectional design of the study limits conclusions about reverse causality. A longitudinal evaluation of dissociative symptoms will allow us to clarify the association between dissociative symptoms and clinical variables. However, we have planned follow-up assessments to counterbalance this limitation. Another limitation is represented by the recall bias of incompleteness and imprecision of the patients' memories and, ultimately, the phases of disorder; in fact, not all patients were in the worst phase during the interview. Therefore, we planned a further study in which we will include only patients in the acute phase of the illness.