Evidence for overlap between idiopathic environmental intolerance and somatoform disorders

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.