In an hypothesis-generating case-control study of amyotrophic lateral
sclerosis. lifetime occupational histories were obtained. The patients
(n = 28) were clinic based. The occupational exposure of interest in
this report is electromagnetic fields (EMFs). This is the first and so
far the only exposure analyzed in this study. Occupational exposure u
p to 2 years prior to estimated disease symptom onset was used for con
struction of exposure indices for cases. Controls (n = 32) were blood
and nonblood relatives of cases. Occupational exposure for controls wa
s through the same age as exposure for the corresponding cases. Twenty
(71%) cases and 28 (88%) controls had at least 20 years of work exper
ience covering the exposure period. The occupational history and task
data were used to classify blindly each occupation for each subject as
having high, medium/high, medium, medium/low, or low EMF exposure, ba
sed primarily on data from an earlier and unrelated study designed to
obtain occupational EMF exposure information on workers in ''electrica
l'' and ''nonelectrical'' jobs, By using the length of time each subje
ct spent in each occupation through the exposure period, two indices o
f exposure were constructed: total occupational exposure (E(1)) and av
erage occupational exposure (E(2)). For cases and controls with at lea
st 20 years of work experience, the odds ratio (OR) for exposure at th
e 75th percentile of the E(1) case exposure data relative to minimum e
xposure was 7.5 (P < 0.02; 95% CI, 1.4-38.1) and the corresponding OR
for E(2) was 5.5 (P < 0.02; 95% CI, 1.3-22.5). For all cases and contr
ols, the ORs were 2.5 (P < 0.1; 95% CI, 0.9-8.1) for E(1) and 2.3 (P =
0.12; 95% CI, 0.8-6.6) for E(2). This study should be considered an h
ypothesis-generating study. Larger studies, using incident cases and i
mproved exposure assessment, should be undertaken. (C) 1997 Wiley-Liss
, Inc.