Euthymic patients with bipolar disorder (BD) and remitted patients with major depressive disorder show reduced hedonic capacity compared with mentally healthy individuals, Italian researchers report.
The findings suggest that altered hedonic capacity is not a state-related feature of depression, but represents an enduring trait in patients with affective disorders, say Marco Di Nicola (Catholic University Medical School, Rome) and colleagues.
"Our finding of residual anhedonic symptoms in euthymic bipolar patients could have implications for pathophysiology because it is suggestive of persistent, trait-related changes in the neurobiological mechanisms that underpin pleasure, motivation and reward," they comment in the Journal of Affective Disorders.
The team assessed 107 euthymic BD patients, 86 remitted patients with MDD, and 106 mentally healthy controls using the Snaith-Hamilton Pleasure Scale (SHAPS), the anhedonia/asociality subscale of the Scale for the Assessment of Negative Symptoms (SANS), and a 10-point visual analogue scale (VAS) for hedonic capacity.
The three groups were similar in terms of mean age, gender distribution, and education level.
The researchers found that BD and MDD patients had significantly higher SHAPS total scores than controls (1.86 and 2.01 vs 1.14), as well as significantly higher SHAPS subscale scores for interests (0.60 and 0.57 vs 0.30) and social interactions (0.77 and 0.76 vs 0.45).
In addition, BD and MDD patients had significantly higher scores than controls on the SANS anhedonia/asociality subscale (3.81 and 3.83 vs 0.94) and the VAS for hedonic capacity (4.25 and 4.35 vs 3.50).
The difference in scores on all three scales between BD and MDD patients was not significant.
The team also note that 20.5% and 24.5% of BD and MDD patients, respectively, had a SHAPS total score of 3.00 or higher, indicating low hedonic capacity (anhedonia), compared with just 7.5% of controls.
Di Nicola et al conclude: "Our findings support the notion that altered hedonic capacity is involved in the pathogenic mechanism of bipolar disorder and could represent a trait-like feature."
They add: "This understanding is of significance in terms of unraveling the neuropathophysiology of anhedonia as well as from a clinical perspective. Stable, enduring anhedonic features could, in fact, create vulnerability to future bouts of mood disorder episodes and determine a poorer functional outcome."
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