Abstract
Multiple chemical sensitivity (MCS) is a common condition, characterized by somatic distress upon exposure to odors. As in other idiopathic environmental intolerances, the underlying mechanisms are unknown. Contrary to the expectations it was recently found that persons with MCS activate the odor-processing brain regions less than controls, while their activation of the anterior cingulate cortex (ACC) is increased. The present follow-up study was designed to test the hypotheses that MCS subjects have increased harm avoidance and deviations in the serotonin system, which could render them intolerant to environmental odors. Twelve MCS and 11 control subjects, age 22–44, all working or studying females, were included in a PET study where 5-HT1A receptor binding potential (BP) was assessed after bolus injection of [11C]WAY100635. Psychological profiles were assessed by the Temperament and Character Inventory and the Swedish universities Scales of Personality. All MCS and 12 control subjects were also tested for emotional startle modulation in an acoustic startle test. MCS subjects exhibited significantly increased harm avoidance, and anxiety compared to controls. They also had a reduced 5-HT1A receptor BP in amygdala (p = 0.029), ACC (p = 0.005) (planned comparisons, significance level 0.05), and insular cortex (p = 0.003; significance level p<0.005 with Bonferroni correction), and showed an inverse correlation between degree of anxiety and the BP in the amygdala (planned comparison). No group by emotional category difference was found in the startle test. Increased harm avoidance and the observed changes in the 5-HT1A receptor BP in the regions processing harm avoidance provides a plausible pathophysiological ground for the symptoms described in MCS, and yields valuable information for our general understanding of idiopathic environmental intolerances.
Highlights
Multiple chemical sensitivity (MCS) is a common condition
positron emission tomography (PET) Data The results showed that MCS subjects differ from healthy controls with respect to the serotonin system
The present study shows that MCS persons have increased harm avoidance, and specific reductions in the 5-HT1A receptor binding potential (BP) in the amygdala, the anterior cingulate cortex (ACC) and the insular cortex (Figure 3)
Summary
Multiple chemical sensitivity (MCS) is a common condition As in other idiopathic environmental intolerances the mechanisms behind the reported hypersensitivity are unknown. In a random sample of 18 to 69 years old women and men 27% of the 4,242 respondents reported symptoms related to inhalation of airborne chemicals but only 0.5% had made adjustments due to this problem in their social as well as occupational life. Symptoms are triggered at exposure levels well below current exposure limits based on identified health risks. The triggering substances are chemically unrelated, indicating that no specific toxicological pathway may explain the reported reactions
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