LETTER
Controversy over Multiple Chemical Sensitivities
Jacqueline Krohn, MD;
Jill Ryan, BA; and
Julie Jacobson, PhD, MS, RN
1 February 1994 | Volume 120 Issue 3 | Pages 249-251
TO THE EDITOR:
Simon and colleagues [1] appear to present a case–control study comparing chemically sensitive patients with controls without specific and measurable prestudy hypotheses. The results are useful only to develop recommendations for future studies, and only if the study was done adequately. However, flaws in participant selection and the information collected probably biased their results.
Simon and colleagues selected patients with a computer billing code of multiple allergy, and then screened for illness lasting 3 months or more, multisystem involvement (including the central nervous system), and self-report of sensitivity to chemicals. With no screening for length, type or severity of exposure, level of sensitivity, or degree of illness, confounding variables remain unaddressed. Controls were not screened for sensitivity to chemicals, masked regular exposures, or previous occupations that could have provided chemical exposures. Bell and colleagues [2] report that in a random group of 643 college students, 15% report symptomatic response to chemicals. Musculoskeletal and back injury occur predominantly in "blue collar" occupations such as manufacturing, where chemical exposures are common.
Cases and controls were then matched for age, sex, and educational level, insufficient criteria that may have missed important factors. We argue that dilution of cases and controls through systematic error in participant selection, combined with a poor response rate and small sample size, severely biased the results of this study.
Diagnosing mental illness when patients are known to have central nervous system dysfunction and multiple system symptoms is difficult. A presupposition of a healthy central nervous system exists in measures of depression and anxiety. Where known central nervous system dysfunctions exist, these measures are less valid. The validity of the somatization scale is lowest of all Diagnostic Interview Schedule measures [3]. Using this diagnostic tool on a group of patients with variable multiple system symptoms and unclear cause only emphasizes inherent problems with validity.
Research has shown memory impairment in persons exposed to chemicals who were chosen under careful criteria [4] and brain damage with related emotional and functional disruption from exposure to chemicals [5]. For future study of environmental sensitivity, development of clear classification systems and identification of confounding variables should be priorities.
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Author and Article Information
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Los Alamos Medical Center; Los Alamos, NM 87544
1. Simon GE, Daniell W, Stockbridge H, Claypoole K, Rosenstock L. Immunologic, psychological, and neuropsychological factors in multiple chemical sensitivity: a controlled study. Ann Intern Med. 1993; 19:97-103.
2. Bell IR, Schwartz GE, Peterson JM, Amend D. Self-reported illness from chemical odors in young adults without clinical syndromes or occupational exposures. Arch Environmental Health. 1993; 48:6-13.
3. Robin LN, Helzer JE, Croughan J, Ratcliff KS. National Institute of Mental Health Diagnostic Interview Schedule. Its history, characteristics, and validity. Arch Gen Psychiatry. 1981; 38:381-9.
4. Fledler N, Maccia C, Kipen H. Evaluation of chemically sensitive patients. J Occup Med. 1992; 34:529-38.
5. Morrow LA, Callender T, Lottenberg S, Bucshsbaum MS, Hodgson MJ, Robin N. PET and neurobehavioral evidence of tetrabromoethane encephalopathy. J Neuropsychiatry Clin Neurosci. 1990; 2: 431-5.
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