Chemical sensitivity: the scientific literature

Multiple Chemical Sensitivity: It's time to catch up to the science

Multiple chemical sensitivity (MCS) is a complex medical condition associated with low dose chemical exposures. MCS is characterized by diverse features and common comorbidities, including fibromyalgia, cough hypersensitivity, asthma, and migraine, and stress/anxiety, with which the syndrome shares numerous neurobiological processes and altered functioning within diverse brain regions. Predictive factors linked to MCS comprise genetic influences, gene-environment interactions, oxidative stress, systemic inflammation, cell dysfunction, and psychosocial influences. The development of MCS may be attributed to the sensitization of transient receptor potential (TRP) receptors, notably TRPV1 and TRPA1. Capsaicin inhalation challenge studies demonstrated that TRPV1 sensitization is manifested in MCS, and functional brain imaging studies revealed that TRPV1 and TRPA1 agonists promote brain-region specific neuronal variations. Unfortunately, MCS has often been inappropriately viewed as stemming exclusively from psychological disturbances, which has fostered patients being stigmatized and ostracized, and often being denied accommodation for their disability. Evidence-based education is essential to provide appropriate support and advocacy. Greater recognition of receptor-mediated biological mechanisms should be incorporated in laws, and regulation of environmental exposures.

Social economic factors and the risk of multiple chemical sensitivity in a Danish population-based cross-sectional study: Danish Study of Functional Disorders (DanFunD)

OBJECTIVES

Multiple chemical sensitivity (MCS) is a rare multisystem and poly-symptomatic disease characterised by a report of various somatic symptoms attributed to inhalation of volatile chemicals in usually harmless doses. The aim was to explore four selected social factors and the risk of MCS in the general Danish population.

DESIGN

A cross-sectional general population-based study.

SETTING

The Danish Study of Functional Disorders was conducted from 2011 to 2015 which included 9656 participants.

PARTICIPANTS

A total of 8800 participants were included in analyses after observations with missing data on exposure and/or outcome were excluded. A total of 164 cases fulfilled the questionnaire criteria for MCS. Of the 164 MCS cases, 101 reported no comorbid functional somatic disorder (FSD) and were included in a subgroup analysis. A total of 63 MCS cases fulfilled the criteria for at least one additional FSD, this subgroup was not included in further analysis. The remaining study population without MCS or any FSD were regarded as controls.

OUTCOME MEASURES

We used adjusted logistic regression to calculate OR and 95% CIs of MCS and MCS without FSD comorbidities for each social variable separately including education, employment, cohabitation and subjective social status.

RESULTS

We found an increased risk of MCS among the unemployed (OR: 2.95, 95% CI: 1.75 to 4.97), and a twofold increased risk of MCS among individuals with low subjective social status (OR: 2.00, 95% CI: 1.08 to 3.70). At the same time, 4 years or more of vocational training were protective of MCS. No significant associations were observed among MCS cases with no comorbid FSD.

CONCLUSION

Lower socioeconomic status was found to be associated with a higher risk of having MCS but not with MCS without FSD comorbidities. Due to the cross-sectional design of the study, we cannot determine whether social status is a determinant or a consequence of MCS.

Chemical intolerance: involvement of brain function and networks after exposure to extrinsic stimuli perceived as hazardous

Background

Chemical intolerance (CI) is a chronic condition characterized by recurring and severe symptoms triggered by exposure to low levels of odorous or pungent substances. The etiology of CI has been a controversial subject for a long time. The aim of this review is to summarize findings on the neurological processing of sensory information during and after exposure to low levels of odorous or pungent substances in individuals with CI, focusing on the brain function and networks.

Methods

Scientific studies on CI published between 2000 and 2019 in academic peer-reviewed journals were systematically searched using medical and scientific literature databases. Only peer-reviewed articles reporting original research from experimental human studies directly associated with CI, and involving related neurological responses or brain imaging after exposure to odorous or pungent substances (i.e., in chemical provocation tests), were considered.

Results

Forty-seven studies were found to be eligible for a full-text review. Twenty-three studies met the selection criteria and were included in this review. Evidence indicated that differences between subjects with CI and healthy controls were observed by brain imaging during and after exposure to odorous or pungent substances. Differences in brain imaging were also observed between initial exposure and after exposure to these substances. Neurological processing of sensory information after exposure to extrinsic stimuli in the limbic system and related cortices were altered in subjects with CI. A previous documentable exposure event was likely to be involved in this alteration.

Conclusions

This review documents consistent evidence for the altered neurological processing of sensory information in individuals with CI. Further neurophysiological research exploring the processing of extrinsic stimuli and cognition of sensation through the limbic system and related cortices in CI, and the appearance of symptoms in individuals with CI, are required.

Differences in psychological and somatic symptom cluster score profiles between subjects with Idiopathic environmental intolerance, major depression and schizophrenia

Idiopathic Environmental Intolerance (IEI) has been associated with psychogenic factors and an increased number of comorbid psychiatric disorders such as depression and anxiety disorder. The purpose of the current study was to examine a possible overlap of psychological and somatic symptoms between subjects with IEI and patients with major depression and schizophrenia as well as to specify characteristic differences. The different symptom clusters included symptoms of chemical intolerance, neurotoxicity and psychological distress as well as measurements of mental health such as anxiety, depression, somatoform symptoms, and schizophrenia-specific disturbances in cognitive domains. IEI patients reported higher overall levels in physical symptoms such as chemical intolerance, neurotoxicity and somatic symptoms not attributable to an organic cause. Schizophrenia patients showed higher overall levels in self-experienced disturbances in several schizophrenia-specific cognitive domains, whereas general psychological distress, anxiety and depression were rated highest by patients with major depression. Importantly, the groups markedly differed in the shapes of profiles of various symptom clusters. Our results provide evidence that IEI patients can be distinguished on the phenomenological level from patients with major depression or schizophrenia, and that distinct domains of psychological and somatic symptoms are particularly problematic in specific diagnostic groups.

Application of Quick Environment Exposure Sensitivity Inventory (QEESI©) for Japanese population: study of reliability and validity of the questionnaire

A standardized questionnaire has not been established for screening or diagnostic assessment of patients with multiple chemical sensitivity (MCS) in Japan. In the US, Miller and Prihoda (1999a, b) developed a questionnaire that could be used internationally, the Quick Environment Exposure Sensitivity Inventory (QEESI©), to assist researchers and clinicians in evaluating patients and populations for chemical sensitivity. The Japanese version of QEESI©was subsequently translated by Ishikawa and Miyata (1999). The present study was performed to investigate the reliability and validity of QEESI©(Japanese version) for research purposes and for evaluation of patients with MCS in Japan.

A total of 498 subjects were recruited from the general population of Miyagi prefecture, Japan. The factor structure in QEESI©was analyzed with 40 items on four subscales except for the items in ‘Masking’ using principal components analysis with Promax rotation. The results showed that 30 items on three subscales, ‘Chemical Inhalant Intolerances,’ ‘Symptom Severity,’ and ‘Life Impact’ except for ‘Other Intolerances’ were consistent with those reported for the US population by Miller and Prihoda (1999a). Cronbach’s a reliability coefficient ranged between 0.87 and 0.94 indicating high internal consistency in the 30 items on three subscales.

Next, we compared the mean scores on three subscales of QEESI©in two groups: 131 self-reported MCS group who were new outpatients at the Environmental Medical Center in Kitasato Institute Hospital, and 131 members of the general population (controls) who were matched for both gender and age with the self-reported MCS group. Mean scores on each subscale for the self-reported MCS group were significantly greater than those for controls (PB < 0.001). Mean scores on all of the 30 items on three subscales for the self-reported MCS group were also significantly greater than for the controls (PB < 0.001). These findings indicated that the 30 items on three subscales in QEESI©can be used for surveys and for diagnostic assessment of patients with MCS as well as for comparative studies between patients in Japan and in other countries.

Rating of Olfactory Judgements in Migraine Patients

The aim of this study was to evaluate olfactory hypersensitivity (OHS) between attacks in migraine patients. Seventy-four migraine patients and 30 controls were enrolled. The presence of OHS was evaluated using an oral questionnaire and a chemical odour intolerance index. Subjects had to rate the intensity and hedonicity of 12 odourants using a linear rating scale. Twenty-six patients (35.2±) but no control subjects reported an interictal OHS ( P < 0.001). Logistic regression analysis showed that patients with OHS presented a greater attack frequency, a higher number of odour-induced migraines and visual hypersensitivity when compared with other patients. Disease duration, age, gender and auditory hypersensitivity were not associated with OHS. OHS patients judged odours less pleasant than did other patients and controls, whereas the intensity scores were identical in both groups. OHS between attacks was significantly associated with odour-triggered migraine and an alteration of hedonic judgement.

Allergological and toxicological aspects in a multiple chemical sensitivity cohort

Background. Multiple chemical sensitivity (MCS) is a chronic condition characterized by an exaggerated response to toxicants. We ascertained the prevalence of allergy to metals and toxicological aspects in MCS patients. Methods. We conducted a retrospective review of medical records of 41 patients with MCS. We performed patch testing (n = 21) for dental series and did lymphocyte transformation test (n = 18) for metals. We measured mercury in samples of blood (n = 19), urine (n = 19), saliva (n = 20), and scalp hair (n = 17) to investigate the association between mercury levels and cases of MCS. Results. The prevalence of metal immune hypersensitivity in a subset of 26 patients was 92.3 percent. Elevations of mercury occurred in 81.2 percent (26 of 32). The mean (±SD) in blood concentrations of mercury was 7.6 ± 13.6 μg/L; mean in urine was 1.9 ± 2.5 μg/L; mean in scalp hair was 2.2 ± 2.5 μg/g; mean in saliva was 38.1 ± 52.1 μg/L. Subgroup analyses showed that elevation of mercury levels in biological matrices were associated with mercury amalgams in patients with MCS (22 patients), compared with controls (8 patients) (odds ratio 11 : 95 percent confidence interval 1.5 to 81.6; P = 0.023). Conclusions. Our data show an increased prevalence of metal allergy and elevation of mercury levels in bioindicators among patients with MCS.

Evaluation of genetic polymorphisms in patients with multiple chemical sensitivity

Objective

Multiple chemical sensitivity (MCS) is a chronic medical condition characterized by symptoms that the affect an individual’s response to low-level chemical exposure. In this study, we identified a chemical sensitive population (CSP) and investigated the effect of genetic polymorphisms on their risk of chemical sensitivity.

Methods

A quick environment exposure sensitivity (QEESI) questionnaire was used to survey 324 Japanese male workers whose DNA samples had been collected and stored. The following genes, which encode enzymes affecting the metabolic activation of a large number of xenobiotic compounds, were selected and analyzed in order to determine their influence on genetic predisposition to CSP: cytochrome P450 (CYP) 2E1, N-acetyl transferase (NAT) 2, glutathione S-transferase (GST) M1, GSTT1, GSTP1, low Km aldehyde dehydrogenase (ALDH2), and superoxide dismutase (SOD) 2.

Results

Significant case-control distributed differences were observed in SOD2 polymorphisms and allele frequency distribution in high chemical sensitive subjects. Both the significant adjusted OR of 4.30 (95% CI, 1.23–15.03) and 4.53 (95% CI, 1.52-13.51) were observed in SOD2 Ala/Ala and Val/Ala compared to Val/Val and in SOD2 Ala/Ala compared to Val/Ala compared to Val/Val genetic analysis in the high chemical sensitivity case-control study.

Conclusions

We observed that high chemical sensitive individuals diagnosed by using Japanese criteria as MCS patients were more significantly associated with SOD2 polymorphisms.

Psychophysiologic treatment for patients with medically unexplained symptoms: a randomized controlled trial

BACKGROUND

Patients presenting with medically unexplained physical symptoms (MUPS) typically present with significant distress and marked impairment in functioning and pose a unique challenge to health care providers. The purpose of this study was to examine the efficacy of a psychophysiological treatment (PT) for MUPS.

METHODS

Thirty-eight participants meeting criteria for subthreshold somatization disorder (abridged somatization) were randomly assigned to one of two conditions: (1) standard medical care augmented by a psychiatric consultation intervention (wait-list) or (2) a 10-session, manualized, individually-administered PT added to the psychiatric consultation intervention. Assessments were conducted at baseline, at midpoint (after four sessions), and after completing the last session. The primary outcome measure was the severity scale of the Clinical Global Impression Scale anchored for Somatic Symptoms (CGI-SD). Secondary outcome measures were responder status as determined by clinical ratings, self-report measures of mental and physical functioning.

RESULTS

At the end of the trial, the severity (and frequency) of physical symptoms improved significantly more (p<0.05) in the intervention group. The average improvement in the CGI-SD was 0.80 points greater in the intervention group than in the wait-list group. PT was also associated with greater improvements in self-reported functioning and depressive symptomatology. The effect sizes at the final assessment point indicate that this intervention had a robust effect on complex somatic symptom presentations.

CONCLUSION

For patients with high levels of MUPS (abridged somatization), PT produces significant improvements in symptoms and functional status.

Resistance to extinction in an odor-20% CO2 inhalation paradigm: further evidence for a symptom learning account of multiple chemical sensitivity

OBJECTIVE

Multiple chemical sensitivity (MCS) is characterized by a variety of symptoms in response to nontoxic concentrations of chemicals. To further test a laboratory model of MCS based on symptom learning, we used a stronger respiratory challenge in this study than in previous studies to induce symptoms (20% CO(2)-enriched air, unconditioned stimulus). Additionally, extinction of learned symptoms was investigated.

METHODS

Diluted ammonia (AM) and butyric acid (BA) served as conditioned (odor) stimuli (CSs). In a learning phase, healthy participants received three breathing trials of BA mixed with CO(2) and three trials of AM mixed with regular air, or the reversed combination. In a test phase, the same trials were administered without CO(2). Immediately after odor onset, participants rated their anxiety and expectancy to experience symptoms during that trial. Self-reported symptoms were assessed after each trial; respiratory behavior was measured throughout the experiment.

RESULTS

Only participants who learned to correctly anticipate symptoms (learning phase) reported elevated symptoms in response to the CS+ odor (test phase). Anticipation was more likely correct and learned symptoms were more elevated when BA had been previously associated with CO(2). Across test trials, anticipatory anxiety diminished, but learned symptoms did not. Participants failing to learn the prearranged contingencies reported overall more symptoms and anxiety.

CONCLUSIONS

Strong respiratory challenges impede extinction of learned symptoms. Conscious expectancy, which may be modulated by odor quality, determines whether learned symptoms develop in response to a specific odor or to the general context. The results further support a symptom learning account of MCS.

US-inflation in a differential odor-conditioning paradigm is not robust: relevance for medically unexplained symptoms

Reported somatic symptoms without clear relation to physiological processes are studied. A learning paradigm was used with two odors (CSs) and the inhalation of CO(2)-enriched air (US), while measuring symptom levels and respiratory behavior. After paring one odor with the CO(2)-enriched air and the other odor with air, half of the participants received a US-inflation manipulation (information manipulation and enhanced US). Subsequently, all participants received both odors with air (test). A difference between the odor previously paired with CO(2)-enriched air and the odor previously paired with air was found for the symptom measure, US-expectancy ratings, and, to a lesser extent, for respiratory volume. No differences, however, were found between the group receiving the US-inflation manipulation and a group not receiving this manipulation. The results indicate that, despite a successful learning of reported symptoms, US-inflation does not seem to be robust.

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.

Physiologic and symptomatic responses to low-level substances in individuals with and without chemical sensitivities: a randomized controlled blinded pilot booth study

We conducted a pilot study using a randomized, single-blind, placebo-controlled exposure among 10 individuals with and 7 without reported chemical sensitivities in a dedicated testing chamber. Objectives of the study were to explore the length of the adaptation period to obtain stable readings, evaluate responses to different substances, and measure the level and type of symptomatic and physiologic reactions to low-level exposures. Reported and observed symptoms, electrodermal response, heart rate, skin temperature, surface electromyogram, respiratory rate, contrast sensitivity, and the Brown-Peterson cognitive test were used and compared between cases and controls and between test substances (glue, body wash solution, dryer sheet) and control substances (unscented shampoo and clean air). Subjects with chemical sensitivities (cases) took longer to adapt to baseline protocols than did controls. After adaptation, despite small study numbers, cases displayed statistically significant responses (all measures, p < 0.02) in tonic electrodermal response to test substances compared with controls and compared with the control substance. Symptoms were also higher in cases than in controls for the body wash solution (p = 0.05) and dryer sheets (p = 0.02). Test-retest showed good agreement for both symptoms and tonic electrodermal responses (McNemar's test, p = 0.32 and p = 0.33, respectively). Outside of skin conductance, other measures had no consistent patterns between test and control substances and between cases and controls. This study shows the importance of using an adaptation period in testing individuals with reported chemical sensitivities and, despite small numbers, raises questions about underlying mechanisms and level of reactivity to low-level chemical exposures in sensitive individuals.

Multiple chemical sensitivity syndrome (MCS)--suggestions for an extension of the U.S. MCS-case definition

PURPOSE

To validate and extend the US case definition for the Multiple Chemical Sensitivity Syndrome (MCS) from 1999 by a systematic literature-review.

DATA SOURCE

MEDLINE-research from 1997 to August 2003, research in the Cochrane-Library in August 2003, earlier reviews since 1997.

STUDY SELECTION

Headings and abstracts were screened by one reviewer. All references dealing with multiple chemical sensitivities (MCS) which covered topics of interest such as symptom-profiles, differential diagnostic procedures, etc. were included in the analysis.

DATA EXTRACTION AND SYNTHESIS

Topic-specific data extraction and synthesis was done by one reviewer. Data interpretation was discussed by all other authors.

RESULTS

Out of 1429 references 36 publications proved to be suitable for the review. The results can be summarized as follows: exposure-related symptoms associated with self-reported multiple chemical sensitivities can be divided into non-specific complaints of the central nervous system--CNS (main characteristics) and functional disturbances in other organ systems (optional complaints). There is a significant overlap of MCS, CFS and fibromyalgie. At present no standards for a diagnostic procedure based on the criteria outlined above are existing

CONCLUSIONS

MCS should only be diagnosed in patients who are mainly suffering from exposure-related non-specific complaints of the Central nervous system. The suggested diagnostic procedure follows the guidelines for CFS which are extended by diagnostic clarification of functional disturbances in other organ systems.

An integrative approach considering acute symptoms and intensity ratings of chemosensory sensations during experimental exposures

Even at low concentrations airborne chemicals can excite olfactory and trigeminal receptors and inform the organism about the presence of airborne chemicals. Acutely, malodors or sensory irritations might trigger symptoms (e.g., bad air quality, eye irritations) and in the long-run functional impairment of chemoreception might occur. In humans, knowledge about short-term adaptational processes and effects of exposure peaks on these systems is limited. Therefore, two different experiments with human volunteers were conducted. In experiment A exposures (4h) with fluctuating concentrations of 2-ethylhexanol (1.5, 10, 20ppm C(TWA)) were investigated, experiment B used similar but constant vapor concentrations. Olfactory- and trigeminal-mediated symptoms and intensities of odor, eye, and nasal irritations were recorded. All measures showed a dose-dependent response and peak exposure effects. In the course of the 4h exposures solely olfactory symptoms decreased. Nasal irritations remained nearly unchanged across the 4h, eye irritations slightly increased. Inter-individual differences related to the personality trait of self-reported chemical sensitivity had only minor effects on chemosensory symptoms in experiment B and no effect on intensity ratings in both experiments. Chemosensory effects seem to be amplified by exposure peaks and less adaptive than assumed.

Repeated low level formaldehyde exposure produces enhanced fear conditioning to odor in male, but not female, rats

Multiple chemical sensitivity (MCS) is an ill-defined disorder in humans attributed to exposure to volatile organic compounds. This study draws on apparent parallels between individuals with posttraumatic stress disorder (PTSD) and panic disorder and a subset of those reporting MCS, using a conditioned fear task in rats. Male and female Sprague-Dawley rats were given repeated exposure to 2 ppm formaldehyde (Form) (1 h/day x 5 days/week x 4 week) or air, and after 2-3 weeks, rats were trained on the conditioned fear task. One half of Air and Form rats were given odor (orange oil, the conditioned stimulus, CS) paired with footshock (PRD) and the other half was given the same stimuli in an unpaired manner (UNP). After 24 h, rats were placed into the same context without the CS or footshock. Male and female PRD groups demonstrated contextual freezing 5-15% of the time, while the UNP groups showed freezing 30-50% of the time, with no effect of Air or Form pretreatment. For the next 5 days, rats were placed into a novel context and tested for freezing in the absence or presence of the CS. In male rats, Form pretreatment produced a significantly greater freezing response in both UNP and PRD groups in the presence of the CS, with no differences in freezing in the absence of the CS. In female rats, no significant differences between Form pretreated rats and Air controls were observed in either the PRD or UNP groups. The increase in conditioned fear responding to the CS after Form exposure in males suggests that repeated low-level Form may act as a stressor to produce sensitized responding within olfactory/limbic pathways, and may help explain the panic-like responses observed in a subset of individuals reporting MCS. Furthermore, the male/female differences suggest a gonadal hormonal contribution to this behavior.

Intranasal effects in chemically sensitive volunteers: an experimental exposure study

During inhalational exposure to irritants stimulation of the trigeminal nerve endings in the nasal mucosa or other biochemical mechanisms might initiate inflammatory processes. Increased sensitivity of this physiological system in response to chemical stimulation is postulated in subjects reporting chemical intolerance. In the present study 12 subjects reporting chemical sensitivity and 12 controls were exposed to different concentrations of the industrial solvents ethyl benzene and methyl ethyl ketone (MEK). Concentrations of various inflammatory biomarkers, namely eosinophil cationic protein (ECP), myeloperoxidase (MPO), interleukin 1β (IL-lβ), substance P (SP), and neurokinin A (NKA) were measured in nasal secretion after exposures. Before, during, and after the exposures subjects rated the severity of nasal irritations. The biomarker concentrations and reported irritations were not affected by the exposures. Regardless of substance and concentration sensitive subjects reported more nasal irritations. In conclusion, the investigated substances might possess weaker potency to elicit intranasal irritative effects than postulated.

Multiple chemical sensitivity and idiopathic environmental intolerance (part two)

Multiple chemical sensitivity/idiopathic environmental intolerance (MCS/IEI) is a commonly used diagnostic term for a group of symptoms without apparent organic basis. The symptoms are characteristic of dysfunction in multiple organ systems. They wax and wane fluctuate according to exposure to low levels of chemical agents in the patient's environment, and sometimes begin after a distinct environmental change or injury such an industrial accident or chemical introduced after remodeling. Although traditional medical organizations have not agreed on a definition for this syndrome, it is being increasingly recognized and makes up an increasing percentage of the caseload at occupational/environmental medical clinics.Part two of this review article discusses diagnosis, clinical examination, long-term follow up of MCS/IEI, and the role of physicians, research on odor and treatment, diseases with similar symptoms, and further research regarding MCS/IEI patients.

Multiple chemical sensitivity and idiopathic environmental intolerance (part one)

Multiple chemical sensitivity/idiopathic environmental intolerance (MCS/IEI) is a commonly used diagnostic term for a group of symptoms. These symptoms have been described and commented on for more than 15 years in the USA. Recently, it has also been observed in Japan. The main features of this syndrome are multiple symptoms involving in multiple organ systems that are precipitated by a variety of chemical substances with relapses and exacerbation under certain conditions when exposed to very low levels which do not affect the population at large. There are no laboratory markers or specific investigative findings. Although traditional medical organizations have not agreed on a definition for this syndrome due to the lack of obvious evidence to demonstrate the existence of these symptoms, it is being increasingly recognized. It constitutes an increasing percentage of the caseload at occupational/environmental medical clinics.Part one of this review article discusses pathophysiological theories, substances which cause symptoms, prevalence in the general and specific populations, past history and family history, and clinical symptoms of MCS/IEI patients.

Odor perception in patients with multiple chemical sensitivity

Since symptoms typical for multiple chemical sensitivity (MCS) are induced by exposure to low levels of chemicals, we hypothesize that MCS represents an impaired recognition of odors or an increased emotional reaction to common odors. Twenty-five subjects with MCS, 20 women and 5 men, and 50 gender-and-age matched controls participated in this study. The University of Pennsylvania Smell Identification Test (UPSIT) and the Cross-Cultural Smell Identification Test (CC-SIT) were administered. In addition to selecting the most probable odor among the four, the subjects were asked their impression of each odor. Odor identifiability evaluated by the scores of two tests, were almost equal in MCS and control groups. The mean CC-SIT odor per person with pleasant feeling was lower in MCS than in controls. The mean odor per person creating an unpleasant sensation was higher in MCS than in the controls. Gingerbread was the only odor making MCS subjects more pleasant than the controls. Nine out of 40 UPSIT odors were felt as unpleasant by MCS subjects more than by controls. This study indicates that MCS subjects are able to identify the odors equally as well as the controls but feel unpleasant to a larger number of odors than the controls. Despite unknown mechanisms of the altered odor perception in MCS, the application of these tests for diagnostic procedure of MCS is proposed.

Anxiety sensitivity and depression in multiple chemical sensitivities and asthma

Patients with sensitivities to multiple chemicals report symptoms of cognitive dysfunction, respiratory distress, and mood disturbance. Lifetime and current psychiatric disorders, personality traits associated with symptom reporting, and tests of cognitive function were compared between 30 subjects with Multiple Chemical Sensitivities (MCS), 19 asthmatics, and 31 healthy controls. Relative to asthmatics and controls, more MCS subjects met criteria for current depression and somatization disorder. MCS subjects and asthmatics scored significantly higher than controls on scales of chemical odor intolerance and anxiety sensitivity, both of which were significant predictors of physical symptoms. Few differences on objective neuropsychological tests were noted. However, MCS subjects with comorbid depression performed significantly worse on a verbal memory test relative to asthmatics but not to controls. Anxiety and depression are significant contributors to the physical and cognitive symptoms of MCS subjects.

The vomeronasal organ and chemical sensitivity: a hypothesis

Environmental exposures to very low levels of airborne chemicals are associated with adverse symptoms, often affecting multiple organ systems, in the phenomenon of chemical sensitivity (CS). Recent surveys suggest a significant prevalence of chemically sensitive subjects in the United States, but the mechanism linking exposure to symptoms remains unclear, despite the advancement of a variety of theoretical models. In many of these models, exposure of the nasal respiratory system to an airborne agent is the first step in the pathway leading to symptoms. In this article, we advance the hypothesis that interactions between environmental chemicals and the vomeronasal organ (VNO) may play a role in the etiology of CS. The VNO, a bilateral, tubular organ located in the nose, serves in animals as part of a sensitive chemosensory system; however, evidence suggesting that the VNO retains a functional role in the adult human is controversial. Reported characteristics of the human VNO relevant to CS, including location, prevalence, selective sensitivity to airborne chemical exposure, and capacity to produce systemic effects, are discussed within the context of this ongoing debate. Beyond relevance to CS, the demonstration of an active, adult VNO could have significant impact on environmental toxicology.

Environmental factors in medically unexplained symptoms and related syndromes: the evidence and the challenge

Symptoms, and especially those without clear underlying medical explanations, account for a large percentage of clinical encounters. Many unexplained symptoms have been organized by patients and practitioners into syndromes such as chronic fatigue syndrome, multiple chemical sensitivity, sick building syndrome, Gulf War syndrome, and the like. All these syndromes are defined solely on the basis of symptoms rather than by medical signs. Some of the above-described conditions overlap strongly with explained conditions such as asthma. The relationship of such symptoms and syndromes to environmental exposure is often sharply debated, as is the distinction between the various syndromes. This leads to problems of what type of research should be conducted and who should conduct it. It is time to develop a comprehensive research agenda to sort out nomenclature, epidemiology, and environmental causation for these conditions, moving toward comprehensive and effective public health and clinical approaches.

Responses to panic induction procedures in subjects with multiple chemical sensitivity/idiopathic environmental intolerance: understanding the relationship with panic disorder

Idiopathic environmental intolerance (IEI), also known as multiple chemical sensitivity, is a clinical description for a cluster of symptoms of unknown etiology that have been attributed by patients to multiple environmental exposures when other medical explanations have been excluded. Because allergy has not been clearly demonstrated and current toxicological paradigms for exposure-symptom relationships do not readily accommodate IEI, psychogenic theories have been the focus of a number of investigations. A significantly higher lifetime prevalence of major depression, mood disorders, anxiety disorders, and somatization disorder has been reported among patients with environmental illness compared with that in controls. Symptoms often include anxiety, lightheadedness, impaired mentation, poor coordination, breathlessness (without wheezing), tremor, and abdominal discomfort. Responses to intravenous sodium lactate challenge or single-breath inhalation of 35% carbon dioxide versus a similar breath inhalation of clean air have shown a greater frequency of panic responses in subjects with IEI than in control subjects, although such responses did not occur in all subjects. Preliminary genetic findings suggest an increased frequency of a common genotype with panic disorder patients. The panic responses in a significant proportion of IEI patients opens a therapeutic window of opportunity. Patients in whom panic responses may at least be a contributing factor to their symptoms might be responsive to intervention with psychotherapy to enable their desensitization or deconditioning of responses to odors and other triggers, and/or may be helped by anxiolytic medications, relaxation training, and counseling for stress management.

Is multiple chemical sensitivity a clinically defined entity?

In 1996 a WHO/IPCS Workshop has suggested to use as an appropriate descriptor of MCS the broader term "Idiopathic Environmental Intolerances (IEI)", in order to incorporate "a number of disorders sharing similar symptomatologies". Research was strongly encouraged. The following points have been put forward as a precondition to define MCS as a clinical entity: (a) establishment of diagnostic criteria, (b) identification of pathogenic mechanisms, together with, (c) an explanation of relationship between exposures and symptoms. Against this background, progress made in the fields of sensory physiology and neurobehaviour research must be debated. In particular, recent results on processing of cognitive stimuli have to be considered. IEI/MCS patients exhibited differences vs. controls in their reactions to intranasal challenge, consistent with changes in cognitive processing of suprathreshold chemosensory information. Trait anxiety and focus of attention have clearly been identified as major components in eliciting neurobehavioural MCS symptoms. Hence, the question as to whether MCS should be regarded as a clinically defined entity remains controversial, but important progress can be noticed in elucidating and defining the nature of this phenomenon, by a combined effort of several disciplines (toxicology and behavioural toxicology, psychology and psychophysiology, and clinical medicine). The new situation will call for a re-evaluation of traditional positions.

Mechanisms of multiple chemical sensitivity

Sensitivity to chemicals is a toxicological concept, contained in the dose-response relationship. Sensitivity also includes the concept of hypersensitivity, although controversy surrounds the nature of effects from very low exposures. The term multiple chemical sensitivity has been used to describe individuals with a debilitating, multi-organ sensitivity following chemical exposures. Many aspects of this condition extend the nature of sensitivity to low levels of exposure to chemicals, and is a designation with medical, immunological, neuropsychological and toxicological perspectives. The basis of MCS is still to be identified, although a large number of hypersensitivity, immunological, psychological, neurological and toxicological mechanisms have been suggested, including: allergy; autosuggestion; cacosomia; conditioned response; immunological; impairment of biochemical pathways involved in energy production; impairment of neurochemical pathways; illness belief system; limbic kindling; olfactory threshold sensitivity; panic disorder; psychosomatic condition; malingering; neurogenic inflammation; overload of biotransformation pathways (also linked with free radical production); psychological or psychiatric illness; airway reactivity; sensitisation of the neurological system; time dependent sensitisation, toxicant induced loss of tolerance. Most of these theories tend to break down into concepts involving: (1) disruption in immunological/allergy processes; (2) alteration in nervous system function; (3) changes in biochemical or biotransformation capacity; (4) changes in psychological/neurobehavioural function. Research into the possible mechanisms of MCS is far from complete. However, a number of promising avenues of investigation indicate that the possibility of alteration of the sensitivity of nervous system cells (neurogenic inflammation, limbic kindling, cacosomia, neurogenic switching) are a possible mechanism for MCS.

Psychological features of subjects with idiopathic environmental intolerance

OBJECTIVES

Idiopathic environmental intolerance (IEI) is associated with unexplained symptoms attributed to non-noxious levels of environmental substances. Clinically, some of the symptoms of IEI overlap with those of panic disorder (PD). We have recently reported a link between IEI and panic responses to a single inhalation of 35% carbon dioxide (CO(2)), a reliable panic induction challenge. This study assessed depression, stress, anxiety, and agoraphobic symptoms among IEI subjects from our previous study versus healthy controls.

METHODS

Thirty-six IEI and 37 control subjects with no preexisting psychiatric history were compared on self-report psychological questionnaires.

RESULTS

IEI subjects scored significantly higher than controls on the Agoraphobic Cognitions Questionnaire (ACQ), Depression Anxiety Stress Scales (DASS), and Mobility Inventory for Agoraphobia (MI) (Student's t, P<.05).

CONCLUSIONS

IEI subjects represent a group with morbidity significantly higher than a control population but less than what would be expected for a clinical psychiatric population.

Multiple chemical sensitivity: a review of the theoretical and research literature

Multiple chemical sensitivity (MCS) is a term used to describe a disorder characterized by a vast array of somatic, cognitive, and affective symptoms, the cause of which is attributed to exposure to extremely low levels of a variety of chemicals. Upon examination of the patient with a diagnosis of MCS, objective physical findings and consistent laboratory abnormalities are typically nonexistent. The concept of MCS has ignited considerable controversy in the fields of toxicology, immunology, allergy, psychology, and neuropsychology. Central to the controversy is the disagreement over the extent to which the manifestation of MCS is mediated by psychological factors. Because of the large number of neuropsychological symptoms associated with a diagnosis of MCS, neuropsychologists are increasingly receiving referrats for the assessment of these patients. It is important, therefore, that neuropsychologists become aware of the variety of clinical issues that must be taken into account when assessing an individual with a diagnosis of MCS. The theoretical and research literature on individuals with a diagnosis of MCS is reviewed here.

Conversion disorder and multiple chemical sensitivity: a comparative study of psychological defense strategies

This study compared psychological defensive strategies in two groups of patients with multiple chemical sensitivity (n = 10) and conversion disorder (n = 10) by means of the projective perceptual Defense Mechanism Test. We attempted to create a model for personality assessment based on the test data of prior patients, in which new patients could successively be tested. The overall results indicated that it was possible to separate the clinical groups significantly from a control group and from each other. In comparison to the controls, the clinical groups were characterized by patterns that were more nonemotionally adapted as well by a lateness of perception, but the ways in which the clinical groups maintained this difference were not the same. The multiple chemical sensitivity group was characterized above all by blocking maneuvers, while the main defensive strategy of the conversion disorder group was distortion of content.

Generalization of acquired somatic symptoms in response to odors: a pavlovian perspective on multiple chemical sensitivity

OBJECTIVE

Somatic symptoms that occur in response to odors can be acquired in a pavlovian conditioning paradigm. The present study investigated 1) whether learned symptoms can generalize to new odors, 2) whether the generalization gradient is linked to the affective or irritant quality of the new odors, and 3) whether the delay between acquisition and testing modulates generalization.

METHODS

Conditional odor stimuli (CS) were (diluted) ammonia and niaouli. One odor was mixed with 7.4% CO2-enriched air (unconditional stimulus) during 2-minute breathing trials (CS+ trial), and the other odor was presented with air (CS- trial). Three CS+ and three CS- trials were conducted in a semirandomized order (acquisition phase). The test phase involved one CS+-only (CS+ without CO2) and one CS- test trial, followed by three trials using new odors (butyric acid, acetic acid, and citric aroma). Half of the subjects (N = 28) were tested immediately, and the other half were tested after 1 week. Ventilatory responses were measured during and somatic symptoms were measured after each trial.

RESULTS

Participants had more symptoms in response to CS+-only exposures, but only when ammonia was used as the CS+. Also, generalization occurred: More symptoms were reported in response to butyric and acetic acid than to citric aroma and only in participants who had been conditioned. Both the selective conditioning and the generalization effect were mediated by negative affectivity of the participants. The delay between the acquisition and test phases had no effect.

CONCLUSIONS

Symptoms that occur in response to odorous substances can be learned and generalize to new substances, especially in persons with high negative affectivity. The findings further support the plausibility of a pavlovian perspective of multiple chemical sensitivity.

Odor perception: multiple chemical sensitivities, chronic fatigue, and asthma

Patients with multiple chemical sensitivities (MCS) often report heightened sensitivity to odors. Odor detection thresholds to phenyl ethyl alcohol (PEA) and pyridine (PYR) were evaluated as a measure of odor sensitivity for 33 MCS subjects, 13 chronic fatigue syndrome subjects, 16 asthmatic subjects, and 27 healthy controls. Odor identification ability (based on University of Pennsylvania Smell Identification Test results) and ratings in response to four suprathreshold levels of PEA and PYR were also assessed. Odor detection thresholds for PEA and PYR and odor identification ability were equivalent for all groups; however, when exposed to suprathreshold concentrations of PEA, MCS subjects reported significantly more trigeminal symptoms and lower esthetic ratings of PEA. No group differences were found in response to suprathreshold concentrations of PYR. In summary, MCS subjects did not demonstrate lower olfactory threshold sensitivity or enhanced ability to identify odors accurately. Furthermore, they were differentiated from the other groups in their symptomatic and esthetic ratings of PEA, but not PYR.

Chemical sensitivity and fatigue syndromes from hypoxia/hypercapnia

The multiple chemical sensitivities syndrome (MCS) and other chronic syndromes causing fatigue, headache and other protean CNS symptoms without observable signs, are proposed to result from hypoxia/hypercapnia (H/H) due to disturbed breathing. The concept is explained in terms of sleep apnea (SA), although H/H could result from causes other than SA. Reasons for considering this etiologic linkage are as follows: 1. MCS symptoms resemble those of SA. 2. The only physical signs associated with MCS (upper airway inflammation and obstruction) can aggravate SA. 3. The only neuropsychiatric finding common among MCS symptomatics, reduced verbal recall, is associated with SA. 4. Many MCS symptomatics attribute onset of their condition to a pesticide or solvent exposure. Solvent neurotoxicity may cause cacosmia, a symptom of MCS and SA. 5. Improved upper airway patency, a first-line therapy in SA, may improve symptoms in some MCS-like conditions. Implications for diagnosis and treatment of MCS are discussed.

A 37-year-old mechanic with multiple chemical sensitivities

A 37-year-old heating, ventilation, and air-conditioning mechanic developed respiratory, musculoskeletal, and central nervous system symptoms associated with a variety of odorous environmental chemicals. Organic disease was not evident, but the patient was distressed by these symptoms and was at risk for becoming disabled by them. His symptoms fit broadly into the condition recognized as multiple chemical sensitivity. Multiple chemical sensitivity is a diagnostic term for a group of symptoms without demonstrated organic basis. The symptoms are characteristic of dysfunction in multiple organ systems, they increase and decrease according to exposure to low levels of chemical agents in the patient's environment, and they sometimes occur after a distinct environmental change or insult such as an industrial accident or remodeling. Although traditional medical organizations have not agreed on a definition for this syndrome, it is being increasingly recognized and makes up an increasing percentage of the caseload at occupational and environmental medicine clinics. Although there is often dispute about whether the symptoms have a functional or organic basis, an informed approach to evaluation, diagnosis, and management and a careful assessment of impairment, disability, and work relatedness are necessary. Careful exclusion of organic causes is critical, and this should be followed by a judicious approach to coping with symptoms.

Occipital lobe meningioma in a patient with multiple chemical sensitivities

BACKGROUND

The concurrent diagnosis of meningioma with increased intracranial pressure has not been reported previously in a patient who meets diagnostic criteria for multiple chemical sensitivities (MCS).

METHODS

A patient who had been evaluated in an occupational medicine practice, and by several other physicians for sensitivity to chemical odors was found to have papilledema and a visual field deficit. The patient met the clinical criteria set forth by Cullen in 1987 for MCS. A magnetic resonance imaging (MRI) scan was performed.

RESULTS

The MRI revealed a large occipital lobe meningioma, which was surgically resected. Removal of the meningioma had little effect on the patient's symptoms. She has been unable to return to her job as a custodian.

DISCUSSION

The etiology of MCS has been disputed and is currently unresolved. Those who evaluate patients with MCS are reminded that meningiomas and other intracranial mass lesions can affect olfaction, and that patients with MCS can have treatable intracranial abnormalities.

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.

Development of a brief questionnaire for screening for multiple chemical sensitivity syndrome

The objective of this study was to identify a parsimonious set of questions that has high sensitivity and specificity for screening for individuals with multiple chemical sensitivity (MCS) syndrome. We performed a cross-sectional survey using a case-control design. Subjects were derived from patients seen at an academically based Occupational and Environmental Medicine Clinic. Cases consisted of patients who fulfilled the Cullen definition for MCS. Controls were patients who had diagnoses excluding MCS and asthma and who were matched to cases by age and sex. Cases and controls filled out a screening questionnaire that, among things, elicited responses as to whether and how subjects reacted to 122 different types of environmental exposures. Data from 44 pairs of cases and controls were available for analysis. The average age of cases was 50.2 years, and 91% was female. Among cases, the most common exposure that was purported to incite MCS was 'indoor air quality contaminants (unspecified)' (59%), followed by solvents (27.3%). After randomly excluding five cases and controls, a stepwise selection procedure for two-group discriminant analysis revealed that the main contributors to the discrimination of the remaining cases and controls were self-reported reactions to copy machine emissions, marking pens, aftershave, window cleaner, nylon fabric, pine-scented products, and rayon material. When a positive response to these factors was used as the sole method for discriminating cases from controls, only one of 41 cases was misclassified as a control while none of the controls was misclassified as a case. When the same method was applied to the five excluded cases and five excluded controls, only one of the five cases was misclassified while none of the five controls was misclassified as a case. Among patients with MCS defined by the Cullen criteria in this clinical setting, having a reaction to these seven common potential exposures comprised a parsimonious set of factors that discriminated between MCS patients and age- and sex-matched normal controls. These questions may have utility in screening for individuals with MCS in general population survey studies.

Exposures of children to organophosphate pesticides and their potential adverse health effects

Recent studies show that young children can be exposed to pesticides during normal oral exploration of their environment and their level of dermal contact with floors and other surfaces. Children living in agricultural areas may be exposed to higher pesticide levels than other children because of pesticides tracked into their homes by household members, by pesticide drift, by breast milk from their farmworker mother, or by playing in nearby fields. Nevertheless, few studies have assessed the extent of children's pesticide exposure, and no studies have examined whether there are adverse health effects of chronic exposure. There is substantial toxicologic evidence that repeated low-level exposure to organophosphate (OP) pesticides may affect neurodevelopment and growth in developing animals. For example, animal studies have reported neurobehavorial effects such as impairment on maze performance, locomotion, and balance in neonates exposed (italic)in utero(/italic) and during early postnatal life. Possible mechanisms for these effects include inhibition of brain acetylcholinesterase, downregulation of muscarinic receptors, decreased brain DNA synthesis, and reduced brain weight in offspring. Research findings also suggest that it is biologically plausible that OP exposure may be related to respiratory disease in children through dysregulation of the autonomic nervous system. The University of California Berkeley Center for Children's Environmental Health Research is working to build a community-university partnership to study the environmental health of rural children. This Center for the Health Assessment of Mothers and Children of Salinas, or CHAMACOS in Monterey County, California, will assess (italic)in utero(/italic) and postnatal OP pesticide exposure and the relationship of exposure to neurodevelopment, growth, and symptoms of respiratory illness in children. The ultimate goal of the center is to translate research findings into a reduction of children's exposure to pesticides and other environmental agents, and thereby reduce the incidence of environmentally related disease.

Olfaction and symptoms in the multiple chemical sensitivities syndrome

Whereas most idiosyncratic environmental sensitivity complaints do not fit known diagnoses, the multiple chemical sensitivities syndrome (MCS) is an extreme presentation that has defined diagnostic criteria. MCS symptomatics claim that they acquired a sensitized state as the result of a chemical exposure, usually to a solvent or pesticide, but not to a fragrance. Before this exposure, they did not experience symptoms. Following sensitization, symptoms increasing in number and severity with time are attributed by the MCS symptomatic to various exposures that are innocuous to most individuals. Although phenomenological studies have provided no evidence that particular odors elicit MCS symptoms, low levels of fragrances and perfumes are frequently associated with the reporting of MCS symptoms. This evaluation examines proposed mechanisms by which odorants and fragrances might cause either sensitization or elicitation of MCS symptoms, including altered odor sensitivity, primary irritancy or irritancy-induced upper airway reactivity, neurogenic switching of trigeminal irritancy signals, time-dependent sensitization and limbic kindling, CNS toxicity, and various psychiatric conditions. In no case was there persuasive evidence that any olfactory mechanism involving fragrance underlies either induction of a sensitized state or the triggering of MCS symptoms. Fragrances and other odorants could, however, be associated with symptoms as claimed by MCS symptomatics, because they are recognizable stimuli, but fragrance has not been demonstrated to be causal in the usual sense.

Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence

This paper summarizes theory and evidence for a neural sensitization model of hyperresponsivity to low-level chemical exposures in multiple chemical sensitivity (MCS). MCS is a chronic polysymptomatic condition in which patients report illness from low levels of many different, structurally unrelated environmental chemicals (chemical intolerance, CI). Neural sensitization is the progressive host amplification of a response over time from repeated, intermittent exposures to a stimulus. Drugs, chemicals, endogenous mediators, and exogenous stressors can all initiate sensitization and can exhibit cross-sensitization between different classes of stimuli. The properties of sensitization overlap much of the clinical phenomenology of MCS. Animal studies have demonstrated sensitization to toluene, formaldehyde, and certain pesticides, as well as cross-sensitization, e.g., formaldehyde and cocaine. Controlled human studies in persons with self-reported CI have shown heightened sensitizability in the laboratory to nonspecific experimental factors and to specific chemical exposures. Useful outcome measures include spectral electroencephalography, blood pressure, heart rate, and plasma beta-endorphin. Findings implicate, in part, dopaminergic mesolimbic pathways and limbic structures. A convergence of evidence suggests that persons with MCS or with low-level CI may share some characteristics with individuals genetically vulnerable to substance abuse: (a) elevated family histories of alcohol or drug problems; (b) heightened capacity for sensitization of autonomic variables in the laboratory; (c) increased amounts of electroencephalographic alpha activity at rest and under challenge conditions over time. Sensitization is compatible with other models for MCS as well. The neural sensitization model provides a direction for further systematic human and animal research on the physiological bases of MCS and CI.

Patterns of waking EEG spectral power in chemically intolerant individuals during repeated chemical exposures

Previous studies indicate that low level chemical intolerance (CI) is a symptom of several different controversial conditions with neuropsychiatric features, e.g., chronic fatigue syndrome, fibromyalgia, multiple chemical sensitivity, and "Persian Gulf Syndrome". Prior studies suggest that limbic and/or mesolimbic sensitization may contribute to development of CI. The purpose of this report was to document the waking electroencephalographic (EEG) patterns of individuals with CI during chemical exposures presented over repeated sessions. Three groups of adult subjects who were recruited from the community participated in the study: self-reported CI who had made associated lifestyle changes due to their intolerance (CI/ LSC), self-reported CI who had not made such changes (CI), and normal controls without self-reported CI. Subjects underwent two sessions involving one-minute EEG recordings during exposures to low level chemical odors (a probe for limbic activation). The CI, but not the CI/ LSC, subjects had increased absolute delta power after the chemical exposures during the second, but not the first, session. The findings support the neural sensitization hypothesis for intolerance to low levels of environmental chemicals in vulnerable individuals. As in human studies of stimulant drug sensitization, those with the strongest past history with sensitizing agents may not show-term sensitization to low level exposures in the laboratory.

Early life stress, negative paternal relationships, and chemical intolerance in middle-aged women: support for a neural sensitization model

This study (ntotal = 35) compared early life stress ratings, parental relationships, and health status, notably orthostatic blood pressures, of middle-aged women with low-level chemical intolerance (CI group) and depression, depressives without CI (DEP group), and normals. Environmental chemical intolerance is a symptom of several controversial conditions in which women are overrepresented, that is, sick building syndrome, multiple chemical sensitivity, chronic fatigue syndrome, and fibromyalgia. Previous investigators have postulated that people with CI have variants of somatization disorder, depression, posttraumatic stress disorder (PTSD) initiated by childhood abuse or a toxic exposure event. One neurobehavioral model for CI, somatization disorder, recurrent depression, and PTSD is neural sensitization, that is, the progressive amplification of host responses (e.g., behavioral, neurochemical) to repeated intermittent stimuli (e.g., drugs, chemicals, endogenous mediators, stressors). Females are more vulnerable to sensitization than are males. Limbic and mesolimbic pathways mediate central nervous system sensitization. Although both CI and DEP groups had high levels of life stress and past abuse, the CI group had the most distant and weak paternal relationships and highest limbic somatic dysfunction subscale scores. Only the CI group showed sensitization of sitting blood pressures over sessions. Together with prior evidence, these data are consistent with a neural sensitization model for CI in certain women. The findings may have implications for poorer long-term medical as well as neuropsychiatric health outcomes of a subset of women with CI. Subsequent research should test this model in specific clinical diagnostic groups with CI.

Integrated defense system overlaps as a disease model: with examples for multiple chemical sensitivity

The central nervous, immune, and endocrine systems communicate through multiple common messengers. Over evolutionary time, what may be termed integrated defense system(s) (IDS) have developed to coordinate these communications for specific contexts; these include the stress response, acute-phase response, nonspecific immune response, immune response to antigen, kindling, tolerance, time-dependent sensitization, neurogenic switching, and traumatic dissociation (TD). These IDSs are described and their overlap is examined. Three models of disease production are generated: damage, in which IDSs function incorrectly; inadequate/inappropriate, in which IDS response is outstripped by a changing context; and evolving/learning, in which the IDS learned response to a context is deemed pathologic. Mechanisms of multiple chemical sensitivity (MCS) are developed from several IDS disease models. Model 1A is pesticide damage to the central nervous system, overlapping with body chemical burdens, TD, and chronic zinc deficiency; model 1B is benzene disruption of interleukin-1, overlapping with childhood developmental windows and hapten-antigenic spreading; and model 1C is autoimmunity to immunoglobulin-G (IgG), overlapping with spreading to other IgG-inducers, sudden spreading of inciters, and food-contaminating chemicals. Model 2A is chemical and stress overload, including comparison with the susceptibility/sensitization/triggering/spreading model; model 2B is genetic mercury allergy, overlapping with: heavy metals/zinc displacement and childhood/gestational mercury exposures; and model 3 is MCS as evolution and learning. Remarks are offered on current MCS research. Problems with clinical measurement are suggested on the basis of IDS models. Large-sample patient self-report epidemiology is described as an alternative or addition to clinical biomarker and animal testing.

Quantitative EEG patterns during nose versus mouth inhalation of filtered room air in young adults with and without self-reported chemical odor intolerances

Individuals who report illness (e.g. nausea, headache) from common chemical odors tend to report CNS symptoms suggestive of olfactory-limbic system involvement. This study compared the resting quantitative electroencephalographic (qEEG) patterns of young adult college students reporting subjectively elevated chemical odor intolerance ratings (HICI) with those of controls reporting little or no odor intolerance (LOCI). Each group was subdivided into those with higher (HIDEP) vs. lower (LODEP) ratings of concomitant depression. Nineteen channels of EEG were recorded during a single session over four separate rest periods, respectively, following baseline, cognitive, chemical exposure and olfactory identification tests. Each recording involved two 30-s, eyes-closed, filtered room air breathing conditions: (1) nose inhalation followed by mouth exhalation and (2) mouth inhalation followed by mouth exhalation. HICI showed significantly less beta 1 (beta 1) over the temporal-central region during nose than during mouth inhalation. Over some temporal and central leads, task, DEP and CI interacted to influence beta 1 as well. For theta (theta), CI differences emerged during nose inhalation after the cognitive task at Cz, after chemical exposures at C3, Cz and C4 and after the olfactory ID task at C4. CI differences emerged during mouth breathing after the olfactory ID task at Cz, C4 and T4. The T5-T6 coronal array showed significant CI differences after chemical exposures during nose breathing and during mouth breathing after the cognitive and olfactory ID tasks. The theta findings in the HICI may be related to reports of disturbed attention in CI.