33
who had been exposed at age 10 to 20 years, gave
results similar to those obtained in 1965. Thus
the Rongelapese do not show a trend toward decreasing thyroid iodine uptake as do North Americans (attributed to increased dietary iodineintake).% The main purposeof the later study, how-
ever, was to see whether the exposed individuals
in the intermediate age group might be developing thyroid failure despite the absence of thvroid
nodules; its results indicated no evidence for this.
( However. as discussed below, some exposed Ron-
gelap people without thyroid abnormaiities are
now showingevidence of reduced function on the
basis of response to TSH stimulation.)
Radioimmunoassays (RIA) for Ty and TSH
have been carried out since 1972 on the exposed
Rongelap group and on other people who have
had thyroid surgery. The results on subjects with
known thyroid lesions are presented in Table 27.
Of the 32 subjects tested, 17 or 53% had at least
one TSH level above the upper limits of normal
(these are in boldface in Table 27). These findings
indicate that the residual thyroid tissue is inadequate to sustain euthyroidism in these cases and
also reflect inadequate adherenceto the prescribed T4 replacement regimen. Inadequate T4
replacementis apparently a chronic problem for
certain patients (Nos. 5, 23, 33, 65, and 72). Ele-
vations of plasma TSH have been observedalso
in a number of exposed people without known
thyroid lesions (the TSH concentration was > 10
U/ml only in subjects No. 71 and 74 — see Table
28 and Appendix 8). Presumably these subjects,
as well as several others with plasma TSH concentration >5 but <10 nU/ml (Nos. 4, 16, 34,
+7, 68, and 78), are not receiving the T, therapy
as regularly as had been hoped. In the Rongelap
control group plasma T, concentrations were determined in 109 subjects. In those with T, <5 pg/
dl (6% of those tested) TSH was determined; no
elevated levels were found (data not shown). Only
1 of 99 Utirik subjects tested has had an elevated
serum TSH level (No. 2232).
These normal findings in the unexposed and
Utirik groups suggest that in the irradiated Rongelap group thereis impaired thyroid function
without palpable lesions which could become
symptomatic in the future. The test results prob-
ably lead to underestimation of the true incidence
of impaired thyroid function, since presumably
manyofthe patients are taking the medication as
directed. It should be noted thatit is the personal
experience of manyof the thyroidologists involved
in this study that it is extremely difficult to make
a clinical diagnosis of hypothyroidism in this population. This difficulty emphasizes the importance
of the plasma TSH measurement, which is now
recognized as the mostsensitive indicatorofprimary thyroid dysfunction. The status of thyroid
function in exposed people without apparentthyroid lesions was further tested with exogenous TSH
in 1974, as described below.
3. Thyroid Status of Exposed Rongelap Peopie
Without Apparent Thyroid Lesions
In preparation for TSH testing of reserve thyroid function, prophylactic Ty medication was discontinued for 2 months before the 1974 survey in
all exposed subjects without recognized lesions.
During the survey, plasma samples were obtained
before and 24 hr after intramuscular injection of
10 units of bovine TSH (Thvrotropar. Armour).
Both sets were analyzed for Ty and the first set
also for TSH. Theresults, and thyroxine-binding
globulin-binding capacities (TBG-binding capacities) in somecases, are given in Table 28. The mean
increment in plasma Ty,following TSH was 2.35
1.2 ug/dl (mean + S.D.). The mean T,priorto
TSH injection was 6.64 1.7 we/dl. Similar tests88
on 13 subjects at the University of Pittsburgh
showed a mean increment in plasma 14 of 4.7=
1.0 pe/dl, and a baseline plasma T, of 7.3 ug/dl
which is not significantly different from that of the
exposed Rongelap group being tested. Thus, the
T4 response to TSH is significantly less (<0.001)
in this group of 26 exposed Rongelap subjects than
in the group of 13 subjects from the United States.
Because of the possibility that the smaller increment in plasma T, 24 hr after TSH in the exposed
subjects was due to factors other than decreased
thyroidal reserve, TSH stimulation tests were
done on 10 euthyroid unexposed Rongelap and
Utirik people during a subsequent survey. The
meaninitial plasma T, in this group was 6.01.7
ug/di; and the mean increment 24 hr after TSH
injection was 4.2 1.3 wg/dl, significantly greater
{ p<0.001) than in the exposed subjects.
These results and the finding of elevated plasma
TSH levels suggest that there is underlying,clini-
cally inapparent, thyroid damage in the exposed
Rongelap population. Whileit is conceivable that
the T, replacement program mayhaveled to decreased thyroid reserve, the test results indicate a
need for continued close follow-up of the exposed