4.2 Comparison with previous studies
Some population databases have shown an increased cardiovascular risk in
mild SCH. In Australia, and a reanalysis of the cohort Whickham Survey
in Great Britain, an increase was found in both fatal and nonfatal
ischemic cardiovascular disease.11,22 In Taiwan, an
increase was shown in only fatal cardiovascular
disease.12 A study evaluated the correlation between
mild SCH and scores on the Framingham scale for predicting
cardiovascular risk. A significant positive correlation was found only
in the female population.23 The limitations of the
studies mentioned include the fact that due to their basis in population
databases, these are no studies designed to evaluate the association.
Another limitation is that populations with cardiovascular risk factors
were included, and although the results were adjusted, possible
confounders may remain.
Other studies have evaluated the association of SCH with atherosclerosis
markers. Masaaki et al. evaluated the pulse wave velocity in mild SCH in
comparison to controls. They found greater pulse wave velocity in mild
SCH, indicating a higher degree of atherosclerosis and endothelial
stiffness. One difference with our study is that the mean population age
was higher (65.2 ± 0.57 years).9 Another marker for
atherosclerosis that has suggested an increase in cardiovascular risk in
SCH is the reduction in flow-mediated dilation. The mean of TSH was 12.5
± 8.6 µIU/mL, higher than in our study.16
Unal et al. evaluated the carotid intima-media thickness in children
with mild SCH (age 8.1 ± 3.6 years). As with our study, the intima-media
thickness was greater with SCH in comparison with HC (0.5 ± 0.19 mm and
0.4 ± 0.0 mm, respectively, p=0.001). In children with mild SCH, they
also observed an increase in total cholesterol, LDL, total
cholesterol/HDL, and LDL/HDL. A limitation of this study is that there
was no regression analysis performed to confirm the significance of SCH
as an independent variable in carotid intima-media
thickness.24 A difference with our study is that we
did not obtain a significant difference in the level of lipids in SCH in
comparison to HC.
A study evaluated the association of mild SCH with nonfatal ischemic
cardiac disease in postmenopausal women, with no association found. The
age of the population was higher than in our study, with an average of
> 60 years.13 Rhee et al. evaluated the
association between mild SCH and fatal ischemic cardiac disease in
populations with and without cardiac insufficiency. No association was
demonstrated in the population with a history of cardiac insufficiency
(population with greater cardiovascular risk). The mean age of the
population was higher (59.2 ± 19.2 years) than in our
study.14 Selmer et al. found a slight reduction in
mortality by all causes in patients with mild SCH in a population with
an average of <60 years.25 One of the
limitations of the aforementioned studies is that they were based on
population databases, without a design established to evaluate the
association. Another limitation is that populations with cardiovascular
risk factors were included, limiting the results of the
association.13,14,25
Treatment is currently recommended in SCH with TSH >10
µIU/mL. Treatment in mild SCH is recommended only in populations with
goiter, pregnancies, progression in TSH levels, and/or symptoms
suggesting hypothyroidism with positive anti-TPO. However, the symptoms
of hypothyroidism can be subjective.10
As in this, other studies have shown an improvement in the
cardiovascular system following the use of levothyroxine in mild SCH.
Razvi et al. found a reduction in fatal and nonfatal ischemic cardiac
disease. The population age range was 40 to 70 years. However, in the
subgroup with ages >70 years, no significant changes were
observed.26 Also, the change in flow-mediated dilation
with the use of levothyroxine was evaluated. An increase in this
variable was obtained three months after treatment began, which suggests
an improvement in endothelial function. The mean age of the population
was <60 years,27 as was the case in our
study. An improvement in cardiac contractility in a population with a
mean age <40 years was also observed.28,29
In our study, in the three baseline groups, we obtained a weak positive
correlation between carotid intima-media thickness and the anti-TPO
level. A study evaluated the anti-TPO level with the presence of
atherosclerosis in cardiac catheterization. No association was
found.30 Wells et al. also did not find a difference
in cardiovascular risk factors in populations with or without
anti-TPO.29
In terms of the carotid intima-media, thickening is considered a
measurement of >0.9 mm. 31,32 In our
study, the mean carotid intima-media thickness was <0.9 mm in
the three baseline populations. Despite the foregoing, significant
differences were found among the groups. In a study that evaluated the
carotid intima-media thickness in subjects with OH and ages
<65 years, the researchers also found a mean of <0.9
mm.33 Selcan Koç et al. evaluated the carotid
intima-media thickness in a population of 20 to 90 year-olds. Only in
the group >70 years was thickness >0.85 mm. It
is proposed that the cohort value for the thickening of the intima-media
should be evaluated according to age.34 The
reproducibility in the carotid intima-media measurements has been
evaluated in other studies. High intraobserver and interobserver
intraclass correlation coefficients have been found of 0.97 and 0.98,
respectively.18,35