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Patients presenting with functional somatic syndrome (FSS) are common, and the symptoms are persistent and difficult to treat for doctors and costly for society. The aim of this study was to clarify the common pathophysiology of FSS, especially the relationship between hypothalamic-pituitary-adrenal (HPA) axis function and psychological characteristics of patients with FSS. The subjects were 45 patients with FSS and 29 healthy controls. Salivary free cortisol was measured in the morning, and psychological tests examining depression, anxiety and quality of life (QOL) were performed on the same day. In patients with FSS, depressive scores showed a significant negative correlation with salivary free cortisol in the morning, although in healthy controls, cortisol showed a significant positive correlation with depressive scores. In addition, the correlation between other psychological test scores and cortisol secretion in patients with FSS contrasted with that of controls. The relationship between cortisol and depression, anxiety or QOL, suggests that the HPA axis of patients with FSS is dysfunctional and does not function properly when patients with FSS are under stress. This dysfunction may explain the pathology of medically unexplained persistent symptoms of patients with FSS.

Fibromyalgia syndrome (FMS) is characterized by systemic pain of unknown etiology, and is often accompanied by various psychological symptoms. In the present study, differences in surface electromyographic (SEMG) levels of the trapezius muscle, skin temperature (TEMP) and skin conductance level (SCL) were compared between the right and left side of the body in 31 FMS and 47 control subjects (Control Group). We observed significant asymmetries of SEMG level, TEMP and SCL in the FMS Group. These asymmetries might be related to central, peripheral and autonomic nervous system dysfunctions. Marked increase of SEMG levels, and a decrease of TEMP and SCL were observed at the dominant side in the FMS Group, and a negative correlation of SEMG levels with TEMP and SCL was found. These results suggest that continued antalgic postures in response to pain at the dominant side in FMS patients might lead to asymmetries of SEMG level, TEMP and SCL. Thus, a focus on pain related behaviors and muscle asymmetry might be a useful therapeutic approach.

Mind-body interactions are important in functional somatic syndromes (FSS). Therefore, in the assessment of the psychophysiological stress response in patients with FSS, both subjective feelings and psychophysiological activity should be simultaneously measured. In this study, "Objective Tension Score" (OTS) was defined as an objective parameter of tension; it consisted of surface electromyography and skin conductance level as indicators of muscle and mental tension, respectively. "Subjective Tension Score" (STS) was defined as a subjective parameter of tension. Changes in OTS and STS in response to the stress task were investigated in 30 FSS patients and 28 controls. Objective tension was significantly hyporeactive to the stress task and STS was significantly higher in the patient group than in the control group. There was a significant negative correlation between OTS response and STS in the patient group, but no significant correlation in the control group. Our results suggested the existence of dissociation between subjective and objective responses in FSS patients. This may indicate that FSS patients had difficulty with the awareness of bodily feelings, thus supporting the concept of "alexisomia" or "escaped bodily feelings" in FSS patients.