Background: Many patients who are first seen with what has been called multiple chemical sensitivity syndrome (MCS) experience symptoms suggestive of panic disorder including chest tightness, shortness of breath, palpitations, paresthesias, light-headedness, and mental confusion. Although such patients are often convinced that these symptoms reflect toxic effects of environmental "chemicals," direct evidence of this is lacking. To the contrary, a previous study has shown that some of these individuals exhibit hyperventilation responses on exposure to non-noxious stimuli, and it has been suggested that the resulting hypocarbia accounts for their symptoms. We postulated that some patients with self-identified MCS had an underlying condition similar to panic disorder and would therefore demonstrate similar responses to provocative challenges, such as sodium lactate infusion.
Methods: Patients referred to an allergy and clinical immunology service for evaluation of "chemical sensitivity" were investigated to rule out underlying medical conditions, including asthma, as a cause of their symptoms and were enrolled for study after giving informed consent. After a standardized psychiatric assessment was performed, patients underwent single-blind intravenous infusions of normal saline solution (placebo) and sodium lactate (which reproduces symptoms in individuals with underlying panic disorder). All patients were referred for independent psychiatric assessment.
Results: The standardized psychiatric assessment identified four of five patients as meeting DSM III-R diagnostic criteria for panic disorder along with other depressive and/or anxiety-related disorders. All five patients with self-identified chemical sensitivity exhibited a positive symptomatic response to sodium lactate compared with placebo infusion. Independent psychiatric assessment confirmed the diagnosis of panic disorder on the basis of DSM III-R criteria in each of the five patients.
Conclusion: These results suggest that MCS may have a neurobiologic basis similar, if not identical, to that of panic disorder. We speculate that treatments with demonstrated efficacy in panic disorder may also be of benefit in MCS, and conversely, treatments that reinforce anticipatory anxiety and avoidance behavior in patients with MCS may be detrimental.