What is multiple chemical sensitivity syndrome?

Quick Answer
An increasing intolerance to commonly encountered chemicals at concentrations well tolerated by other people.
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Causes and Symptoms

Multiple chemical sensitivity (MCS) syndrome, idiopathic environmental intolerance (IEI), reactive airway disease, and sick building syndrome are overlapping disorders caused by intolerance of environmental chemicals. Exactly how many people are affected by MCS is unknown. The onset is often associated with initial acute chemical exposure; patients may report the onset of MCS after moving into a new house, being exposed to chemicals in the workplace, or using pesticides in the home. Patients often describe an increasing intolerance to commonly encountered chemicals at concentrations well tolerated by other people. Diagnosis is made when the following six criteria are met: repeated exposure reproduces symptoms, the condition is chronic, low chemical exposure levels cause symptoms, symptoms improve with the removal of offending chemicals, responses are triggered by multiple unrelated chemicals, and multiple systems are affected.

Symptoms usually wax and wane with exposure and are more likely to occur in patients with preexisting histories of migraine or classical allergies. Idiosyncratic medication reactions (especially to preservative chemicals) are common in MCS patients, as are dysautonomic symptoms (such as vascular instability), poor temperature regulation, and food intolerance. It is thought that patients with MCS have organ abnormalities involving the liver, the nervous system (including the brain and the limbic, peripheral, and autonomic systems), the immune system, and perhaps porphyrin metabolism, probably reflecting chemical injury to these systems. There is often a substantial overlap of MCS symptoms with fibromyalgia and chronic fatigue syndrome.

The common clinical symptoms may include headaches (often migraine), chronic fatigue, musculoskeletal aching, chronic respiratory inflammation (rhinitis, sinusitis, laryngitis, asthma), attention-deficit disorder, and hyperactivity in younger children. Less common complaints include tremor, seizure, and mitral valve prolapse. Agents associated with the onset of MCS include gasoline, kerosene, natural gas, pesticides (especially chlordane and chlorpyrifos), organic solvents, new carpet and other renovation materials, adhesives and glues, fiberglass, carbonless copy paper, fabric softener, formaldehyde and glutaraldehyde, carpet shampoo (lauryl sulfate) and other cleaning agents, isocyanates, combustion products (poorly vented gas heaters, overheated batteries), and medications (dinitrochlorobenzene for warts, intranasally packed neosynephrine, prolonged antibiotics, and general anesthesia with petrochemicals).

It is believed that the mechanisms that lead to MCS may be multifactorial and include neurogenic inflammation (respiratory, gastrointestinal, and genitourinary symptoms), kindling and time-dependent sensitization (neurologic symptoms), and immune activation or impaired porphyrin metabolism (multiple-organ symptoms). Pathological findings of MCS have rarely been examined. A preliminary study of nasal pathology in these patients indicates that they are characterized by defects in the junctions between cells, desquamation of the respiratory epithelium, glandular hyperplasia, lymphocytic infiltrates, and peripheral nerve fiber proliferation. A consistent physiologic abnormality in these patients has not been established.

Psychiatric, personality, cognitive/neurologic, immunologic, and olfactory studies have been conducted comparing MCS subjects with various control groups. Thus far, the most consistent finding is that patients with MCS have a higher rate of psychiatric disorders across studies and relative to diverse comparison groups. Since these studies are cross-sectional, however, causality cannot be implied. Various working groups have proposed several research questions addressing the relationship between neurogenic inflammation and toxicant-induced loss of tolerance with the development of MCS.

Treatment and Therapy

The management of patients with MCS at present involves symptomatic and supportive therapy. There is a general consensus among researchers and clinicians that in order to treat patients with MCS effectively, a double-blind, placebo-controlled study performed in an environmentally controlled facility, with rigorous documentation of both objective and subjective responses, is needed to help elucidate the nature and origin of MCS.


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