Affect intensity measure in bipolar disorders: a multidimensional approach

Background: Emotional dysregulation, characterized by high levels of both arousal and intensity of emotional responses, is a core feature of bipolar disorders (BDs). In non-clinical populations, the 40-item Affect Intensity Measure (AIM) can be used to assess the different dimensions of emotional reactivity.

Methods: We analyzed the factor structure of the AIM in a sample of 310 euthymic patients with BD using Principal Component Analysis and examined associations between AIM sub-scale scores and demographic and illness characteristics.

Results: The French translation of the AIM demonstrated good reliability. A four-factor solution similar to that reported in non-clinical samples (Positive Affectivity, Unpeacefulness [lack of Serenity], Negative Reactivity, Negative Intensity), explained 47% of the total variance. Age and gender were associated with Unpeacefulness and Negative reactivity respectively. 'Unpeacefulness' was also positively associated with psychotic symptoms at onset (p=0.0006), but negatively associated with co-morbid substance misuse (p=0.008). Negative Intensity was positively associated with social phobia (p=0.0005).

Limitations: We cannot definitively exclude a lack of statistical power to classify all AIM items. Euthymia was carefully defined, but a degree of 'contamination' of the self-reported levels of emotion reactivity may occur because of subsyndromal BD symptoms. It was not feasible to control for the possible impact of on-going treatments.

Conclusions: The AIM scale appears to be a useful measure of emotional reactivity and intensity in a clinical sample of patients with BD, suggesting it can be used in addition to other markers of BD characteristics and sub-types.