33
whohad been exposed, at age 10 to 20 vears, gave
results similar to those obtained in 1965. Thus
the Rongelapese do not showa trend toward de-
creasing thyroid iodine uptake as do North Americans (attributed to increased dietary iodine intake). The main purpose of the later study, however, was to see whether the exposed individuals
experience of manyof the thyroidologists invoived
in this study thatit is extremely difficult to make
a clinical diagnosis of hypothvroidism in this pop-
ulation. This difficulty emphasizes the importance
of the plasma TSH measurement, which is now
recognized as the most sensitive indicator of primary thyroid dysfunction. The status of thyroid
in the intermediate age group might be developing thyroid failure despite the absenceof thyroid
function in exposed people without apparentthyroid lesions was further tested with exogenous TSH
gelap people without thyroid abnormalities are
now showingevidence of reduced function on the
basis of response to TSH stimulation.)
3. Thyroid Status of Exposed Rongelap People
Without Apparent Thyroid Lesions
nodules; its results indicated no evidenceforthis.
(However,as discussed below, some exposed Ron-
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 surgerv. The results on subjects with
knownthyroid lesions are presented in Table 27.
Of the 32 subjects tested, [7 or 53% had at least
one TSH level above the upper limits of normal
(these are in boidface in Table 27). These findings
indicate that the residual thyroid tissue is inadequateto sustain euthyroidism in these cases and
also reflect inadequate adherence to the prescribed T, replacement regimen. Inadequate T,
replacementis apparently a chronic problem for
certain patients (Nos. 5, 23, 33, 65, and 72). Ele-
vations of plasma TSH havebeen observed also
in a numberof exposed people without known
thyroid lesions (the TSH concentration was > 10
uU/mi only in subjects No. 71 and 74 - see Table
28 and Appendix 8). Presumably these subjects,
as weil as several others with plasma TSH concentration >5 but <10nU/ml (Nos. 4, 16, 34,
47, 68, and 78), are not receiving the T, therapy
as regularly as had been hoped. In the Rongelap
control group plasma T4 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 Ron-
gelap group thereis impaired thyroid function
without palpable lesions which could become
symptomatic in the future. Thetest results probably lead to underestimation of the true incidence
of impaired thyroid function, since presumably
manyofthe patients are taking the medication as
on
CH
CD
co
directedNggould be noted that itis the personal
in 1974, as described below.
In preparation for TSH testing of reserve thyroid function, prophylactic T, medication was dis-
continued for 2 months before the 1974 survey in
all exposed subjects without recognized lesions.
During the survey, plasma sampies were obtained
before and 2¢4 hr after intramuscularinjection of
10 units of bovine TSH (Thyrotropar, Armour).
Both sets were analyzed for T4 and the first set
also for TSH. The results, and thyroxine-binding
globulin-binding capacities (TBG-binding capaci-
ties) in somecases, are given in Table 28. The mean
increment in plasma T, following TSH was 2.35
1.2 ug/dl (mean + S.D.). The mean T, prior to
TSH injection was 6.64 1.7 pg/dl. Similar tests§8
on 13 subjects at the University of Pittsburgh
showed a mean incrementin plasma Ty, of 4.7
1.0 pe/dl, and a baseline plasma T, of 7.3 ug/dl
whichis notsignificantly different from that ofthe
exposed Rongelap group being tested. Thus, the
T4 response to TSHis significantly less (p<0.001)
in this group of 26 exposed Rongelap subjects than
in the group of 13 subjects from the United States.
Becauseofthe possibility that the smaller incrementin plasma T, 24 hr after TSH in the exposed
subjects was dueto factors other than decreased
thyroidal reserve, TSH stimulation tests were
done on 10 euthyroid unexposed Rongelap and
Utirik people during a subsequent survey. The
mean initial plasma T, in this group was 6.01.7
ug /dl; and the mean increment 24 hr after TSH
injection was 4.21.3 ug/dl, significantly greater
(p<.0.001) than in the exposed subjects.
These results and the finding of elevated plasma
TSHlevels suggest that there is underlying,clinically inapparent, thyroid damagein the exposed
Rongelap population. Whileit is conceivable that
the Ty replacement program may haveled to de-
creased thyroid reserve, the test results indicate a
need for continued close follow-up of the exposed