Reduced hedonic capacity in euthymic bipolar subjects: a trait-like feature?

Background: The aim of our study was to assess hedonic capacity in euthymic bipolar subjects, identifying possible differences compared to remitted unipolar depressed patients and healthy controls.

Methods: 107 subjects with bipolar disorders, 86 with major depressive disorder and 106 healthy controls, homogeneous with respect to demographic characteristics, were enrolled. The following scales were administered: the Snaith-Hamilton pleasure scale (SHAPS), the subscale for 'anhedonia/asociality' of the scale for the assessment of negative symptoms (SANS) and the visual analogue scale (VAS) for hedonic capacity.

Results: Scores on SHAPS total, interests and social interactions, SANS 'anhedonia/asociality' and VAS were all significantly higher in affective disorder patients compared to healthy controls. No difference was found between clinical groups. 20.5% (n=22) of bipolar disorder subjects and 24.5% (n=21) of major depressed subjects showed a significant reduction in hedonic capacity (SHAPS total score ≥ 3), compared to 7.5% (n=8) of healthy controls (χ(2)=12.03; p=.002).

Limitations: Limitations include heterogeneity with respect to pharmacological status and longitudinal course (i.e., 'single' vs. 'recurrent' affective episodes).

Conclusions: The major finding of our study is that euthymic bipolar patients and remitted major depressed patients display residual anhedonic symptoms. This suggests that, in affective disorder patients, altered hedonic capacity could represent an enduring trait and that, possibly, dysfunctions in the neurobiological mechanisms underlying hedonic response and reward processing persist, irrespective of mood state.