Altered core depressive symptom balance in post-COVID fatigue: reduced depressed mood in an exploratory matched historical-control study.

Background: Post-COVID chronic fatigue syndromes are frequently associated with depressive episodes and alterations in reward processing. Anhedonia, a core depressive symptom linked to reward-system dysfunction, may be particularly relevant in this context. Objective: To investigate whether depressive symptoms in individuals with post-COVID-like chronic fatigue syndrome display a distinctive configuration of core depressive features, particularly in the balance between depressed mood and anhedonia. Methods: In an exploratory cross-sectional comparative study with a matched historical control group, patients with post-COVID-like chronic fatigue syndrome were compared with matched controls from a pre-COVID community sample. Groups were matched for age, sex, and overall depression severity. Depressive symptoms were assessed using the Patient Health Questionnaire-9 (PHQ-9), and item-level scores were analyzed. Results: The post-COVID fatigue group and matched historical controls showed comparable overall depressive symptom severity and similar rates of mild and moderate depressive symptoms. However, depressed mood was significantly less pronounced in the post-COVID fatigue group, while anhedonia did not differ significantly between groups. Consequently, the depressed mood/anhedonia ratio was markedly reduced in the post-COVID fatigue group. Conclusions: Depressive symptoms in post-COVID-like chronic fatigue syndrome may show an altered balance between the two core depressive features assessed by the PHQ-9. In this exploratory comparison, the most robust finding was reduced depressed mood in the post-COVID fatigue group, whereas anhedonia was not significantly increased. These findings should therefore be interpreted as preliminary evidence of a different depressive symptom configuration, rather than as demonstration of an anhedonia-dominant phenotype.