Carbon dioxide inhalation challenges in idiopathic environmental intolerance

BACKGROUND: Idiopathic environmental intolerance (IEI) is associated with unexplained physical symptoms, which overlap considerably with those of panic disorder (PD). OBJECTIVE: This study tested the hypothesis that patients with symptoms to suggest IEI exhibit features of PD in response to nonnoxious environmental stimuli. METHODS: A single-blind, case-control 35% carbon dioxide inhalation challenge was conducted at a university-based occupational health unit with the use of standardized psychologic questionnaires involving 36 patients with IEI and 37 healthy control subjects. The main outcome measures included panic attack symptoms and scores on the Anxiety Sensitivity Index, a measure of panic-related anxiety. RESULTS: Patients with IEI scored significantly higher on the Anxiety Sensitivity Index than control subjects did (P <.05). Significantly more patients with IEI (71%) than control subjects (26%) fulfilled panic attack criteria after carbon dioxide (P <.001). Physiologic responses to the challenge were not significantly different between groups. CONCLUSIONS: Results suggest that, similar to patients with PD, patients with IEI display high anxiety sensitivity and in response to carbon dioxide inhalation tend to experience heightened anxiety and panic attacks.