Childhood trauma and bipolar spectrum: a population-based sample of young adults

Introduction: Childhood trauma has been suggested to be involved in susceptibility to bipolar disorder (BP). However, it remains unclear whether the occurrence of childhood trauma is differently distributed in subthreshold bipolar disorder (SBP). Objective: To assess childhood trauma in young adults with SBP, as compared to young adults with BP and population controls (PC). Method: This was a cross-sectional, population-based study. The Mini International Neuropsychiatric Interview (MINI) was used to define the groups with BP (subjects with a lifetime or current manic episode or lifetime or current hypomania with a history of a depressive episode), SBP (subjects with a history of hypomanic episode without lifetime or current depressive episode), and subjects without mood disorders (PC). Childhood trauma was assessed using de Childhood Trauma Questionnaire (CTQ). We investigated differences regarding childhood trauma across the three groups (BP, SBP and PC). Result: Except for sexual abuse, all subtypes of childhood trauma remained associated with the BP group as compared to PC. Additionally, when we compared SBP and BP, significant differences were found only for emotional abuse. No significant differences were found in relation to childhood trauma between the SBP and PC groups after adjusting for confounding factors. Conclusion: These findings suggest that investigating childhood trauma, with a particular focus on emotional abuse, could be considered a preventive measure and potentially improve the prognosis.


Introduction
Bipolar disorder (BP) is a heterogeneous illness involving episodes of severe mood disturbance that affects about 2% of the worldwide population. 1 BP is one of the leading causes of disability worldwide and causes substantial economic burden, thus being considered a public health problem. 2,3 Also, it is associated with high rates of premature mortality due to suicide. 4 However, epidemiological studies suggest that the estimates for this condition are conservative and neglect the growing evidence for a continuum of bipolar spectrum disorder. 5 Patients who have pure hypomania without a prior major depressive episode are now classified as having "other specified bipolar and related disorder" in the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5), which is considered a subthreshold bipolar disorder (SBP), with a prevalence of 3.3%. 6 Nevertheless, the experience of hypomanic symptoms does not necessarily indicate a future diagnosis of BP, as in most cases these symptoms have a benign course, disappearing over time, without being associated with early mood disorders. 5,7 Nevertheless, a subgroup of subjects with subthreshold expression of BP does make the transition to BP. 5 There is evidence suggesting that an important factor that differentiates individuals who make the transition to BP from those who do not is the level of persistence of subthreshold expression of BP over time. 5 Little is known about the factors that influence persistence of subthreshold expression of BP, but it has been suggested that the onset and course of BP are affected by environmental interactions. 8 Identification of the environmental determinants of BP is a major challenge, with implications for the identification of subjects at risk in an early stage of the development of the disorder, making early intervention possible. The occurrence of traumatic events during childhood is probably the most promising environmental determinant so far investigated, and it has been associated with negative outcomes in BP, e.g., early illness onset, worse lifetime course, higher number of comorbid mental disorders, suicide attempts, suicide risk, and treatment resistance. [9][10][11] Despite the consistent finding of a relationship between childhood trauma and BP, few studies have been conducted to assess the association between childhood stressors and SBP.
Thus, the aim of this study was to assess childhood trauma in young adults diagnosed with SBP as compared to young adults with BP and population controls (PC).
Our main hypothesis was that individuals with BP developed full criteria for this disorder because they suffered more traumas in childhood as compared to individuals with SBP. A secondary hypothesis was that there would be few significant differences between the SBP and BP groups, suggesting that they are part of the same spectrum, presenting worse clinical characteristics and higher occurrence of childhood trauma when compared to PC.

Method Design and participants
This was a cross-sectional study corresponding to the second wave of a population-based cohort study.
The full description of the first wave can be found elsewhere. 12 The inclusion criteria at baseline were: 1) to be between 18 15 Childhood trauma was evaluated using the Childhood Trauma Questionnaire (CTQ), in a version adapted to the Brazilian population by Grassi-Oliveira. 16 The CTQ is a 28-item, self-report measure widely used to assess history of childhood abuse and neglect. This instrument can be administered to adolescents (12 years or older) and adults, investigating five traumatic components: emotional, sexual and physical abuse, and emotional and physical neglect. It uses a 5-item Likert scale. 16 Current and lifetime psychiatric disorders were assessed using the Mini International Neuropsychiatric Interview 5.0 (MINI), 17 administered by well-trained psychologists. We defined our groups as follows: subjects without mood disorders (PC); subjects with BP type I or BP type II (BP-I or BP-II); subjects with a history of hypomanic episode without lifetime or current depressive episode (SBP). This last group was defined based on the category described in DSM-5 as "other specified bipolar and related disorders," describing the third diagnostic criterion: "hypomanic episode, lasting for more than 4 days, without prior major depressive episode." Finally, for the proposal of this study, subjects with a diagnosis of depression without a history of manic or hypomanic episode were excluded from the analyses (n = 317).

Statistical analysis
Data were collected using Open Data Kit Collect 1.

Results
In total, 927 young adults were included in the   (Table 3).  14 ; SD = standard deviation. Data presented as n (%) and analyzed using the chi-square test, unless otherwise specified. * One-way analysis of variance (ANOVA).