Table 3.—-Tests of Thyroid Function.in Exposed Marshallese With Evidence of Thyroid Dysiunction*
Subject No./
” Age at Exposure,
yr/Sex
Estimated
Thyroid
Dose, Rad
Age at
Surgery for
Thyrold Nodules, yr
Age
Hypothyroidism
Recognized, yt
To
Bg/eL
(5-10.2)2
TBGI,
Units
{0.85+1.10)+
FY,
Units ~
(4.7-9.7)¢
TSH,
pU/mL
(<6}+
a71IM
SiiiM
1,050-2,100
t,050-2,100
eee
wae
10
10
2.55
0.4
0.95§
o.71
2.4§
0.3
69§
S00
33/1/F
1,050-2,100
13
“413
8.3
0.82
6.8
65/4/F
2/2:F
1,050-2, 100
13
700-1,400
13
~ 7O0-1,400
69/4/F
19/5/M
390-780
B3 sin utero
(=6-mo ceastation) 9 /iM
13
12
15
14
20
20
19
> 175
1.9)
6.5
er:
14
*Bafore thyroid surgery or traatmant for clinical hypothyroidism.
{Usually corresponds to the eartiest abnormal plasma thyrotrophin measurement.
ST
.
,
33
eee
22
eee
ee
‘0.64
5.5
0.9.
470
4.01
5.3
&
0.98
3.2
0.64
22
7
;
.
$95% confidence interval, T, indicates thyroxine; TSGI, thyroxine-binding globulin index: FT,I, free thyroxine index; TSH, thyratrophin (thyroid-stimulating
hormone).
§Plasma obtained in 1977, when levothyroxine sodium therapy had been discontinued by the patient,
iThyroxine iodine (T,!) (normal range, 3.0 to 6.4 ug/dL).
§Mother had an estimated thyroidal dose of 425 rad.
Table 4.—Thyroid Function in Exposed, Unoperated-on Marshallese With Evidenca of Mild Thyroid Dysfunction
-Subject No./
Age at Exposure,
yr/Sex
32/3/M
- A138
’
-
Estimaisd
Thyrold
Dose, Rad
700-1,400,
‘7U/271F
_W8IS7/F oO.
34145/F
_
:”.18/397M
Age
.
_
Recognized,
yr°
29
335 BR
335
51
BBB6B.
335
69
435 “Sst 7 ez):
Ta
” po/db
(5-10.2)t
6.1
54
-
TaGI,
Untts
FT,
(0.851.140)
0.89
"082
Unite
—(4.7-0.7)$
45
increment
After TSH,
#9 of T,/dL
(4.21.3) (SE)
wee
TSH,pU/mb
Basal
(<6.0)~
6.7,7.3
.
_§-
20min
After TRH
(8.4-18.2)t
wee
8A O08 6.07.0 °°: 25
41 1.040
4.3
45
O88 = °° 40 5
48
0.80
3.8
/ 42
‘400 °
‘42
ae
65,7.0_
35
7% + OB2>) 6488 On88.
0.2
6.3,8.3
48
7
Oh" “leaes 0 7 ae
"Usually corresponds to the date of earliest abnormal plasma thyrotrophin (TSH) (>6 ,U/mL)} measurement,
* $95% confidence interval of the responsein euthyroid Marshallese. T, indicates thyroxine: TRGI, thyroxine-binding globulin index; FT.I, tree thyroxine index:
TRH, thyrotrophir-raleasing hormone (protiretin); TSH, thyrotrophin (thyroid-stimutating hormone).
thyroid dysfunction might be a more
common problem in these persons
than was appreciated initially and led
to the broader studies described hereafter.
Retrospective Analyses of Thyroid
Function in Frozen Serum Samples
A limited number of frozen plasma
samples were available that -were
_obtained before surgery. Until 1968,
the determination of T, levels was
dependent on the protein-bound iodine (PBI). Since the Marshallese
people have an increased plasma content of an as yet poorly characterized
iodoprotein, the PBI determinations
gave a falsely high level of T,, possibly masking hypothyroidism.” Hypothyroidism in subjects No. 3 and 5
(Table 3) was first suspected ten
years after exposure, when thesechil-
dren showed growth retardation and
delayed skeletal maturation. It was
not until more specific methods for T,
and TSH quantitation were used that
the clinical diagnosis was confirmed
JAMA, March 19, 1982—Vol 247, No. 11
by chemical measurements (Table 3).
The TSH level was 500 2U/mL and
the FTI was markedly depressed in a
plasma sample from subject No. 5
obtained in 1963. Subject No. 3 was
already receiving levothyroxine re-
placement at the time of the first
sample (still available), but a thyrox-
ine iodine (T,1) of 0.8 pg/dL was found
jn 1965 (normal range, 3.0 to 6.4
pg/dL). Neither subject had had thy-
roid surgery. The results in Table 3
show that the plasma TSH level was
unequivocally elevated in three other
subjects (No. 2, 33, and 69). In these
individuals, hypothyroidism was not
apparent. In subject No. 69, the plas-
ma FTI was markedly depressed, and
it was low normal in subject No. 2.
Since several weeks of thyroid therapy are required to suppress TSH to
normal levels, a norma! plasma FTI
such as found in subject No. 33 in the
presence of an elevated TSH level
probably indicates that levothyroxine
treatment had not been maintained
regularly over the previous months.
In two other persons (No. 19 and 853),
plasma TSH concentrations were
above the upper limits of normal, but
no other samples were available to
confirm these borderline: elevations.
The low (No. 19) or subnormal! (No.
83) FTL is consistent with the diagno-
sis of modest thyroid dysfunction.
Results of Prospective Evaluations
Determinations of TSH levels have
The reason for the apparent discrep-
been performed on two or more ocea-
the serum TSH concentration of 22
pU/mL in subject No. 33 is unclear.
Prophylactic levothyroxine treatment
Ailingnae during the fallout and wha
ancy between the FT,I of 6.8 units and
had already been begun in the Ronge-
lap population in 1965, and this plasma sample was obtained in 1966.
‘of
1 oor
_
S30) 2900 3
ee
eye
th
|
sions in plasma samples from 36
persons who were on Rongelap or
have-not had thyroid surgery. Prephylactic levothyroxine administra-
tion had been discontinued at least
two months previously. In six per
Hypothyroidism and Fallout Exposure~—Larsan et al
57s