Provocative challenges in patients with multiple chemical sensitivity.

Whether multiple chemical sensitivity (MCS) is an organic disease initiated by environmental exposure or a psychologic disorder is a subject of controversy. The identification of pathophysiologic or psychophysiologic mechanisms occurring in patients with MCS after provocative challenges should be illuminating. Fifteen patients with MCS were challenged with their trigger substances and observed clinically. Prechallenge and postchallenge pulmonary function tests and PCO2, PO2, and oxygen saturation were measured. All of the patients whose symptoms were reproduced by the challenge (11 of 15) showed clinical evidence of acute hyperventilation with a rapid fall in PCO2 and no change or a rise in oxygen saturation. The symptoms and signs were consistent with an anxiety reaction with hyperventilation. Pulmonary function was unchanged; and recovery was rapid, aided in two cases by rebreathing into a paper bag. The most logical conclusion is that in these patients the MCS disorder is a manifestation of an anxiety syndrome triggered by their perception of an environmental insult, with at least some of their symptoms induced by hyperventilation.