Predictors of Somatic Symptom Severity in Adult Psychiatric Outpatients: A Cross-sectional Heart Rate Variability and...

To examine the relative contributions of clinical, autonomic, and neurophysiological variables to somatic symptom severity among adults with major depressive disorder (MDD) or attention-deficit/hyperactivity disorder (ADHD).

We analyzed data from 103 outpatients (MDD = 55; ADHD = 48) who completed quantitative electroencephalography (QEEG), heart rate variability (HRV), and questionnaires (Patient Health Questionnaire-15, Beck Depression Inventory-II, Pittsburgh Sleep Quality Index, Korean Adult ADHD Rating Scale). Hierarchical regression models sequentially entered demographics, clinical symptoms, HRV total power, and QEEG beta-band coherence.

The final model explained 49.4% of the variance (adjusted R² = 0.421, p < 0.001). Clinical variables produced the largest increment (ΔR² = 0.232, p < 0.001), with sleep disturbance as the strongest predictor (β = 0.359, p < 0.001), followed by female sex (β = 0.256, p = 0.004) and depressive symptoms (β = 0.207, p = 0.031). Lower HRV total power was significantly associated with greater somatic symptom severity (ΔR² = 0.026, p = 0.034; β = -0.194, p = 0.020). Reduced QEEG beta coherence added value (ΔR² = 0.076, p = 0.048), particularly for right frontofrontal (β = -0.259, p = 0.031) and left frontoparietal (β = -0.245, p = 0.052) connectivity. Primary diagnosis (MDD vs. ADHD) was not predictive (p = 0.124).

Sleep disturbance showed the strongest association with somatic symptoms, followed by female sex and depressive symptoms. Limited role of categorical diagnosis supports a dimensional framework. Reduced autonomic flexibility and disrupted cortical connectivity may underlie bodily distress, warranting confirmation through longitudinal studies.