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Evidence for Overlap Between Idiopathic Environmental Intolerance and Somatoform Disorders

From the Department of Clinical Psychology, Central Institute of Mental Health, Mannheim, Germany (J.B., M.W., C.P.); Department of Dermatology, University Hospital of Mannheim, Germany (C.B.); Psychological Institute I, University of Münster, Germany (F.R.).

Address correspondence and reprint requests to Josef Bailer, PhD, Central Institute of Mental Health, Department of Clinical Psychology, PO Box 122120, 68072 Mannheim, Germany, Federal Republic of Germany. E-mail: bailer{at}zi-mannheim.de

Objective: Idiopathic environmental intolerance (IEI), also known as multiple chemical sensitivity, is a chronic, polysymptomatic condition that cannot be explained by an organic disease. Physical and psychological complaints are believed to be sustained by low levels of chemically unrelated substances in the environment. At present, it is unclear whether IEI is an environmental illness or a variant of somatoform disorders (SFD). This study examined whether IEI can be distinguished from SFD with respect to self-reported symptoms, trait anxiety, body-related cognitions, and symptom attributions.

Methods: We compared 54 subjects with IEI, 54 subjects with SFD but without IEI, and 44 subjects with neither IEI nor SFD on symptom scales, psychological questionnaires, and structured interviews for IEI, depression, anxiety, and SFD.

Results: More than half of the IEI subjects met Diagnostic and Statistical Manual of Mental Disorders, fourth edition criteria of SFD. This group shared both symptoms and psychological features of somatization with the SFD group. IEI subjects who did not fulfill criteria for a specific SFD were less impaired by their chemical sensitivity but differed nevertheless from nonsomatoform controls by significantly higher symptom scores, higher trait anxiety, a focus on autonomic sensations, and more pronounced somatic symptom attributions. These psychological features were significantly associated with the burden of somatic symptoms in both SFD and IEI. Furthermore, self-reported allergy but not total immunoglobulin E correlated with symptom burden in the total sample.

Conclusions: The similarity of IEI and SFD regarding symptoms and psychological features of somatization support the hypothesis that IEI is a variant of SFD.

Key Words: idiopathic environmental intolerance • multiple chemical sensitivity • SFDs • perceptual style • symptom attribution • medically unexplained symptoms

Abbreviations: IEI = idiopathic environmental intolerance; SFD = somatoform disorder; ESQ = Environmental Sensitivity Questionnaire; DSM-IV = Diagnostic and Statistical Manual of Mental Disorders, fourth edition; ANOVA = analysis of variance; SIQ = Symptom Interpretation Questionnaire; PHQ-9 = Patient Health Questionnaire depressive symptom severity scale; PHQ-15 = Patient Health Questionnaire somatic symptom severity scale; SOMS = screening for somatoform symptoms; STAI = State Trait Anxiety Inventory; COSS = Chemical Odor Sensitivity Scale; SCID = Structured Clinical Interview for DSM-IV; ACQ = Agoraphobic Cognition Questionnaire; CABAH = Cognitions about Body and Health Questionnaire.