Somatoform pain disorder (SPD) is frequently associated with sleep disorders, specifically restless legs syndrome and insomnia, which in turn lowers the pain threshold and worsens pain.

The aim of the present study was to investigate differences in wake-EEG by low-resolution electromagnetic tomography (LORETA) and objective and subjective sleep and awakening quality in SPD patients as compared with controls and study acute and chronic effects of trazodone CR on these variables and pain measures.

Fifteen patients with SPD (F45.4) and co-morbid insomnia (F51.0) were compared with 15 controls and participated in a single-blind, placebo-controlled, cross-over study on the acute effect of 100mg trazodone CR, followed by a six-week open titration period. Statistics involved clinical, EEG-LORETA, PSG and psychometry.

LORETA showed reduced power, mainly in the beta band in almost all pain matrix areas (SI, SII, ACC, SMA, PFC, PPC, insula, amygdala, hippocampus). PSG demonstrated a lack of deep sleep and increased arousals and stage shifts, with opposite changes induced by trazodone after acute and chronic therapy. Improvement of sleep was associated with improvement of pain, evaluated by visual-analog scales.

Our LORETA findings demonstrate a dysfunctional pain modulation in SPD. Trazodone induced changes in subjective and objective sleep and awakening quality that were opposite to the differences between SPD patients and controls (key-lock principle) and associated with pain improvement.