Potential Mechanisms in Chemical Intolerance and Related Conditions

Abstract

The symptom of chemical intolerance may occur in isolation, but often occurs in conjunction with other chronic symptoms such as pain, fatigue, memory disturbances, etc. This frequent clustering of symptoms in individuals has led to the definition of several chronic multisymptom syndromes, such as multiple chemical sensitivity, fibromyalgia, chronic fatigue syndrome, and Gulf War illnesses. The aggregate research into these syndromes has suggested some unifying mechanisms that contribute to symptomatology. Multiple lines of evidence suggest that there is aberrant function of numerous efferent neural pathways, such as the autonomic nervous system and hypothalamic‐pituitary axes, in subsets of individuals with these conditions. There is perhaps the greatest evidence for abnormal sensory processing in these syndromes, with a low “unpleasantness threshold” for multiple types of sensory stimuli. Psychological and behavioral factors are known to play a significant role in initiating or perpetuating symptoms in some persons with these illnesses. In the field of pain research, the interrelationship between physiologic and psychologic factors in symptom expression has been well studied. Using both established and novel methodologies, studies have suggested that psychologic factors such as hypervigilance and expectancy are playing a relatively minor role in most individuals with fibromyalgia and that clear evidence exists of physiologic amplification of sensory stimuli. These studies need to be extended to more sensory tasks and to larger numbers of subjects with related conditions. It is of note, though, that existing data on this spectrum of illnesses would suggest that there may be greater psychologic contributions to symptomatology if an illness is defined in part by behavior (e.g., avoidance of chemical exposures) rather than on the basis of symptoms alone.

Altered cortical excitability in subjectively electrosensitive patients: Results of a pilot study

“…Aggregated research concerning the pathophysiology of CMI has suggested that an aberrant function of centrally mediated processes may play a significant role in initiating and/or perpetuating symptoms [13]. In line with these findings, a growing body of literature reports imbalances in nervous system functions in patients with perceived electrical hypersensitivity [14][15][16].…”

Non-termination of sickness behavior as precipitating factor for mental disorders

“…In most of these patients, where low cortisol levels were found, there were also histories of poor coping abilities, multiple major stressful life events, and in women with chronic pelvic pain, high rates of physical and sexual abuse. In fact it would appear that most individuals with serious multiple unexplicable health complaints have previously suffered from clusters of severe infectious complications, physical or emotional trauma [69] -factors earlier in this paper seen to have the ability to predispose to hypofunction of the CRH/HPA-axis and to stimulate the production of pro-inflammatory cytokines. Preliminary indications are that adrenal insufficiency and an above normal sensitivity to the negative feedback may underlie the hypofunction of the HPA-axis [59].…”

“…Controversy still exists as to whether syndromes consisting of subjective health complaints represent several or variations on one general condition. In fact, it has been suggested that most of the multisymptom syndromes like somatoform disorders, fibromyalgia, chronic fatigue syndrome and exposure syndromes such as Gulf War illnesses, sick-building syndrome, illnesses found in women with silicon breast implants, multiple chemical sensitivity and others are related in terms of their stressexposure histories, their psychological profiles, and some neurological alterations [69]. No distinction will therefore be made for the purpose of this discussion.…”

“…In contrast to the predisposition to hyperactivity of the CRH/HPA-axis, our knowledge on the physiological aspects of those mental disorders where hypoactivity of the axis has been reported is rather scant and results often contradictory. Hypocortisolaemia, often accompanied by baseline sympathetic nervous system hypofunction and low serum serotonin and L-tryptophan levels, is reported for subsets of patients with PTSD, fibromyalgia, chronic fatigue syndrome, chemical intolerance and other stress related somatic disorders [59], [69] and [70]. Amongst the disorders where HPA-axis hypoactivity can occur, PTSD differs from the others, not only in its etiology, but also at the level where the suppression occurs.…”

The Constellation of Chronic Low Back Pain and Other Subjective Symptoms

“…24 These terms have common core features. Each of them refers to subjective experiences obviously real to those who undergo them, often to the point of debility; on the other hand, researchers have striven to substantiate the biomedical substrate of such experiences but so far have largely come up empty-handed.…”