Affective lability and affect intensity as core dimensions of bipolar disorders during euthymic period

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Abstract

Bipolar disorders are usually defined by alternative mood states, but a more precise characterization of the euthymic period could provide further insights into the pathophysiology of bipolar disorders. Surprisingly, few studies have investigated core affective dimensions in euthymic bipolar patients. In this study, we assessed 179 euthymic bipolar patients (score < 12 on the Montgomery-Åsberg Depression Scale and a score < 6 on the Bech–Rafaelsen Mania Scale) compared with 86 control subjects using French versions of the Affective Lability Scale (ALS) and the Affect Intensity Measure (AIM). Data were analyzed by logistic regression. Our results showed that euthymic bipolar subjects reported having more intense emotions than controls and also had a higher affective lability. High scores in both affective dimensions were associated with a significantly higher risk for psychiatric axis I comorbidity. Moreover, a high affective lability score was associated with an earlier age of onset for bipolar disease. Affective lability and affect intensity might be two core dimensions of bipolar disorder during euthymic periods, suggesting that bipolar disorder is not circumscribed to mood episodes but also affects emotional reactivity between episodes. Both dimensions could account for the stress reactivity of bipolar patients that may lead to relapses.

Introduction

In current classifications, bipolar disorders are only defined by the presence of thymic episodes without considering the euthymic period. Many studies have investigated this period using the notion of temperament leading to suggestions of new definitions of bipolar disorders. At present, a categorical approach, based on assessment of personality or temperament, is favored (Akiskal et al., 1995, Akiskal et al., 2005, Perugi et al., 2003). Another approach could involve exploring the euthymic period using dimensions instead of multiple and complex personality traits (Siever and Davis, 1991). A core dimension or a vulnerability marker is supposed to reduce complex behaviors into their component parts. This approach could be useful in determining the genetic vulnerability of a disease (Lenox et al., 2002).

Davidson (1998) suggested that the threshold required for a discrete stimulus to evoke an emotional response can differ between individuals. Highly reactive subjects might respond to minor stimuli, whereas less reactive subjects might not react at all. The amplitude of the response might also differ from individual to individual. Leibenluft et al. (2003) suggested that early-onset bipolar patients are more responsive to both positive and negative emotional stimuli than older patients. Finally, studies using multiple trait personality tests have shown that bipolar patients have higher emotional instability scores than controls (Hirschfeld et al., 1986, Solomon et al., 1996), but few studies have looked at specific affective dimensions in bipolar patients (Henry et al., 2001).

We hypothesize that one of the core abnormalities observed in bipolar patients is a hyper-reactivity to environmental stimuli, leading to affective lability and high affect intensity. Affective lability can be defined as a predisposition to marked, rapidly reversible shifts in affective states, extremely sensitive to meaningful environmental events that might induce more modest emotional responses in normal individuals (Siever and Davis, 1991). Intensity of affect, regardless of hedonic tone, refers to individual differences in characteristic emotional arousability or affective reactivity and is considered to be a stable individual difference dimension (Larsen et al., 1986).

We previously (Henry et al., 2001) compared affective lability, affect intensity and impulsivity core dimensions in bipolar type II patients, borderline patients and patients with other personality disorders. We found that bipolar and borderline patients had higher emotional lability scores. However, that study included only a few bipolar patients and they were only type II.

The aim of this study was to investigate for the first time affective lability and affect intensity by comparing euthymic bipolar patients type I and II and control subjects, using self-rating scales. We hypothesized that 1) bipolar patients would show increased reactivity to emotional stimuli during the euthymic period; and that 2) such affective dimensions would be associated with the severity of bipolar disorder.

Section snippets

Subjects

Bipolar patients were recruited from two psychiatric hospitals (Paris and Bordeaux, France). The study was described in detail to the patients, and written informed consent was obtained from all participants. The control group was composed of blood donors with no personal or familial history of affective disorders or suicide attempts. Both patients and control subjects were interviewed using the French version of the Diagnostic Interview for Genetic Studies (DIGS; Nurnberger et al., 1994). This

Sample characteristics

The sample was composed of 179 bipolar patients and 86 control subjects. The mean age for bipolar patients was 39.17 years ± 12.19 versus 41.67 years ± 11.60 for controls (t(2) =  1.585; P = 0.114). There were more women in the bipolar group (n = 112), 62.6% versus (n = 37) 42.5% in the control group (χ2, ddl = 1; P = 0.002). Sixty-six bipolar patients (37.1%) had never married compared with 24 in the control group (27.6%). Furthermore, 71.4% of patients were employed or students compared with 94.9% of

Discussion

This study demonstrates that affective lability and intensity of emotions are higher in euthymic bipolar subjects than in controls, as assessed with two self-rating scales (the ALS and the AIM). Moreover, early-onset bipolar patients exhibited the strongest affective lability, and high scores on both affective dimensions were associated with lifetime comorbidity for anxiety and substance use.

This study shows that these two affective core dimensions characterize bipolar patients during the

Acknowledgments

This research was supported by Institut National de la Santé et de la Recherche Médicale (INSERM), and by grants from Assistance Publique-Hôpitaux de Paris and Ministère de la Recherche (PHRC, AOM98152).

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