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An Exploratory Study of Subgrouping of Patients With Functional Somatic Syndrome Based on the Psychophysiological Stress Response: Its Relationship With Moods and Subjective Variables

From the Department of Psychosomatic Medicine, Kansai Medical University, Osaka, Japan.

Address correspondence and reprint requests to Kenji Kanbara, Department of Psychosomatic Medicine, Kansai Medical University, 10-15, Fumizono-cho, Moriguchi-shi, Osaka, #570-8507, Japan. E-mail: kanbara{at}body-thinking.com

Objective: To study the characteristics and subjective estimations of subgroups of patients with functional somatic syndrome (FSS). A characteristic in patients with FSS was reportedly hyporeactivity in the psychophysiological stress response (PSR).

Methods: The PSR was measured in 59 FSS patients and 41 healthy controls. Autonomic lability scores (ALSs) of six psychophysiological measurements on PSR were calculated. Cluster analysis using the ALSs was performed in the FSS group. A discriminant analysis was also performed to identify the criterion of the subgrouping. Factor analysis scores of the six ALSs, and moods and subjective variables were compared between the subgroups.

Results: Cluster analysis divided the FSS patients into two clusters. Three groups (low-lability, high-lability, and control groups) were compared. All factor scores of autonomic lability significantly differed between the low- and high-lability groups, and between the low-lability and control groups. The mood scores were higher in the high-lability group than in the low-lability group. The duration of suffering was significantly longer in the high-lability group than in the low-lability group. The distributions of symptoms and diagnosis did not significantly differ between the subgroups.

Conclusions: We have tentatively verified that there are two subgroups based on the autonomic lability among FSS patients, which were independent of the type of symptoms and diagnostic category. Autonomic lability is an important axis in the multiaxial diagnosis of FSS.

Key Words: functional somatic syndrome • psychophysiological stress response • autonomic lability • subgrouping • cluster analysis • mood and subjective variables

Abbreviations: FSS = functional somatic syndrome; IBS = irritable bowel syndrome; FMS = fibromyalgia syndrome; FGID = functional gastrointestinal disorder; ALS = autonomic lability score; PSR = psychophysiological stress response; ANS = autonomic nervous system; VAS = visual analogue scale; SEMG = surface-electromyography; TEMP = skin temperature; SCL = skin conductance level; NSSCR = nonspecific skin conductance response; BVPAmp = blood volume pulse amplitude; STS = subjective tension score.