SAN FRANCISCO-- Like the chronic fatigue, Gulf War, and sick-building syndromes, multiple chemical sensitivity (MCS) is a mystery. The medical community cannot explain its etiology or even prove its existence. Thus, many physicians view MCS skeptically and wonder whether it is just another psychosomatic complaint. Nevertheless, the disorder is very real to its victims. These patients report debilitating respiratory and other symptoms that recur and abate from exposure to everyday chemicals, such as those found in household cleaners, perfumes, soaps, and garden sprays.

Some physicians are also certain MCS exists, including Howard M. Kipen, MD, and Susan M. Tarlo, MBBS, who presented data for the existence of MCS at the recent annual meeting of the American College of Chest Physicians.

DETECTING CHEMICAL SENSITIVITY

To diagnose MCS, physicians must first differentiate between illness and disease, stressed Dr. Kipen, a Professor in the Department of Environmental and Community Medicine at the Robert Wood Johnson Medical School, in Piscataway, New Jersey. Illness, he stated, is a subjective experience that patients report or exhibit in their behavior, whereas disease is an identifiable pathophysiologic condition that produces concrete signs on physical examination or in laboratory testing.

MCS, he explained, is an illness. Although there is no agreed-on definition of MCS and, at present, no medical explanation for the disorder, MCS is associated with a fairly standard set of symptoms that affect multiple organ systems. Common respiratory symptoms include cough, chest tightness, and shortness of breath. Patients also often complain of fatigue, joint pain, muscle aches, headache, severe emotional distress, and impaired cognition. Urologic and dermatologic symptoms are less frequently seen. Many patients report that their symptoms flare, then abate, following low-level exposure to specific chemicals, but this finding has yet to be shown in a clinical trial.

The onset may be clearly defined, with patients recalling the time of the exposure, typically at work, that triggered their symptoms. Often, MCS is not linked to a specific event. “That may affect prognosis,” commented Dr. Kipen, explaining that patients with a defined onset often are much more amenable to psychosocial interventions designed to help them cope with symptoms.

An MCS diagnosis is appropriate when symptom duration is at least three months and all other possibilities, such as an allergic reaction or other medical disease, are ruled out. The differential diagnosis must include classic occupational disease, which results from chronic, on-the-job chemical exposure. One way to distinguish this from MCS is to give patients a list of substances and ask them to check those that trigger their symptoms. Patients with occupational disease will check only a few agents; patients with MCS will select many.

This distinguishing feature was found in a 1995 study, in which 705 subjects, many of whom were receiving treatment at an occupational medicine clinic, were given a list of 122 substances.[1] The 43 patients with MCS reported sensitivity to about 40 of these, on average, whereas most of the other patient groups reported sensitivity to between 0 and 10 agents. Only asthma patients approached the MCS group in the number of reported chemical sensitivities, highlighting the need to include asthma in the differential diagnosis.

POSSIBLE MECHANISMS

Toxic, immunologic, neurobiologic, and other causes have been suggested for MCS, said Dr. Tarlo, a Professor in the Departments of Medicine and Public Health Sciences at the University of Toronto in Canada. However, little consistent evidence exists to support these theories, she noted. It is for this reason that Dr. Tarlo prefers the term idiopathic environmental intolerance (IEI), which stresses that the etiology is unknown.

Recent research has focused a great deal on psychologic mechanisms. At least 40% of MCS patients have psychologic disorders, such as somatoform disorders, anxiety disorders, and depression. These disorders often predate the onset of chemical sensitivity, noted Dr. Tarlo; although that suggests a role for psychologic mechanisms in MCS, it is possible that both disorders are secondary to some other unidentified process.

Often, MCS has features in common with panic disorder, such as dyspnea, chest tightness, and anxiety. In fact, some MCS patients appear to develop a reflex panic response to a particular chemical’s odor after an exposure that produces symptoms. “And this may become extended to other unrelated odors,” Dr. Tarlo said.

Patients with MCS are significantly more likely than healthy controls to have a panic response to carbon dioxide challenge, although carbon dioxide produces similar physiologic changes in both groups, she also reported.[2]

“This suggests that some IEI patients may catastrophically interpret physical symptoms,” she concluded.

MANAGING MCS

No single decisive treatment exists for MCS, making the disorder difficult to manage. Dr. Tarlo recommends that treatment begin with awareness of the possibility of MCS, especially after accidental inhalation of a toxic substance. Rapid medical intervention after such an accident might prevent the onset of chemical sensitivity, she noted.

Symptom management includes altering the work environment to minimize chemical exposure and gradually desensitizing patients to odors that trigger MCS symptoms. Wearing a respirator or mask may provide temporary relief of symptoms.

It is also important to optimize medical therapy for allergic rhinitis, asthma, or any other concurrent conditions. However, “you need to be very careful when doing that because these people tend to report lots of side effects from medications,” Dr. Kipen cautioned. Such reports are most likely to be made by MCS patients who are using tranquilizers, antidepressants, or other psy– choactive agents, although these drugs may be helpful in treating the patients’ psychologic symptoms.

Ten to 15 sessions of cognitive therapy with a mental health professional may help MCS patients decrease their disability by teaching them to reduce their response to symptoms. However, many patients reject the idea of mental health care. Physicians may make this treatment option more palatable by explaining that studies have found cognitive therapy useful for patients with other unexplained illnesses, such as chronic fatigue syndrome.[3]

It is vital not to discourage patients from performing their usual activities. “Avoidance often leads to a spiraling disability,” Dr. Kipen said, “disability from work and the inability to participate in life activities.”

--Timothy Begany

References
1. Kipen HM, Hallman W, Kelly-McNeil K, Fiedler N. Measuring chemical sensitivity prevalence: a questionnaire for population studies. Am J Public Health. 1995;85:574-577.

2. Poonai N, Antony MM, Binkley KE, et al. Carbon dioxide inhalation challenges in idiopathic environmental intolerance. J Allergy Clin Immunol. 2000;105(2 Pt 1):358-363.

3. Price JR, Couper J. Cognitive behaviour therapy for adults with chronic fatigue syndrome. Cochrane Database Syst Rev. 2000:CD001027.