The greatest increase in bone mass occurs during puberty, and the amount of bone gained
during adolescence is the major contribution to the peak bone mass (PBM) that occurs
around the age of 30–35 years old. Studies conducted by the National Osteoporosis
Foundation have shown the importance of the timing of the PBM, as it determines the
phase of the life cycle in which the bone mass is optimized.1 In healthy girls, the
earlier the onset of puberty, the greater the body mass and the bone mineral density
(BMD) at the completion of skeletal maturity.2
3
4
5
The PBM varies according to the location in the skeleton. Estimates based on longitudinal
studies performed by the Canadian Multicentre Osteoporosis Study showed the PBM for
the lumbar region occurs between 33 and 40 years of age, and that the PBM for the
hip occurs between 16 and 19 years of age.6
PBM is influenced by genetic factors, nutritional status, adequate endocrine function,
and physical activity, and is the major determinant of the future risk of fractures
in elderly women.7 Among the endocrine factors are gonadal, adrenal and pituitary
hormones; and, in women, estradiol plays a key role. Estradiol acts on the bones through
several mechanisms and exerts an antiresorptive action.8 According to some authors,
estrogens also act on the bones by indirect mechanisms through an action in the muscles
by evidencing an interrelationship between mechanical forces and the action of steroids
and growth factors on the tissue masses of both the bones and the muscles.9
Several clinical situations that lead to hypoestrogenism are associated with BMD loss
by leading to osteopenia and osteoporosis. The most typical known situation is the
menopausal period. However, when hypoestrogenism occurs in the pubertal period and
in adolescence, it may result in a PBM reduction in these young women. Amenorrheic
adolescents have a lower BMD compared to those who menstruate regularly. The earlier
the hypoestrogenic condition is established and the longer it is extended, the greater
the repercussions on bone mass, with an increased risk of fractures. Several conditions
can lead to hypoestrogenism in young women, such as hypothalamic amenorrhea, hyperprolactinemia,
and premature ovarian insufficiency (POI), among others.8
10
11
Premature ovarian insufficiency is a clinical syndrome defined by the depletion of
the follicular activity before the age of 40 years old. It is characterized by amenorrhea,
increased gonadotrophins (follicle-stimulating hormone [FSH] > 25 mIU/mL) and low
levels of estradiol.11 The incidence of POI in the general population is 1%, and it
represents 6% to 10% of the causes of amenorrhea in general, and 10% to 15% of the
causes of primary amenorrhea. There is a family history of the disease in 4% of the
patients.11 Patients with POI have a pattern in bone turnover markers similar to the
one found in the menopausal state.12
13
14
15
16
17
18 This is an important concern for the health of young women with POI, particularly
if they have not yet reached PBM.
Compared to women who experience menopause at normal ages, patients with POI have
a 1.5-fold greater risk of fracture.19 Some studies have shown a lower BMD in women
with POI or in the menopause before the age of 45 years old by any etiology. Compared
to women who menstruate regularly, women with POI, karyotype 46, XX (mean age: 32
years; range: 20–39 years) had significantly lower BMD Z-scores. About 20% of these
women had a BMD Z-score < 2.0, which indicates a low BMD for their age and a fracture
risk factor.20
A delay in the diagnosis greatly contributes to worsening the BMD.21 It is very common
to find patients with amenorrhea who have already lost precious time in doctors' offices
and basic health units without the doctor investigating for a diagnosis of POF. In
cases of amenorrhea, the possibility of POI should always be considered, and an effective
search should be performed regarding the clinical picture (the climacteric symptoms
of women) and high dosage of serum FSH. After the POI diagnosis, bone vitality should
always be addressed because a loss in bone mass may have already occurred, and this
should be a primary concern with the health of young women with POI.22
23
24
The treatment for osteopenia and osteoporosis caused by hypoestrogenism is essential
and fundamentally based on the administration of estrogen replacement, which is indicated
as a mandatory procedure as long as formal contraindications and patient acceptance
are respected.11
25
Densitometry is directly related to estradiol levels.26 Bone mineral density correlates
positively with body fat (%), fat distribution and estradiol levels, and estradiol
and age were among the factors associated with L2–L4 BMD.27 Levels below 20 pg/mL
may have protective effects on the bone mass. Women with undetectable levels of estradiol
(< 5 pg/mL) were at a 2.5-fold higher risk of fracture compared to women with estradiol
levels between 5 pg/mL and 25 pg/mL.28
29
Thus, smaller estrogen dosages are required to meet bone maintenance needs. Low doses
of estrogen, especially when associated with calcium, have a positive effect on bone
mass, and its action appears to be predominantly on reabsorption, but not on bone
formation after the age of 70 years old.30
We must always remember that there are several other goals of hormone replacement
therapy (HRT) besides prevention and treatment of secondary bone loss due to ovarian
failure. Therefore, the needs of each patient should be taken into account in order
to define the estrogen dose to be administered. Further studies are needed to prove
the efficacy of lower estrogen doses for cardiovascular protection, vasomotor phenomena,
etc.
A three-year prospective randomized clinical trial was conducted by the United States
National Institutes of Health (NIH) in young women with POI, karyotype 46, XX, in
order to investigate the efficacy of a standardized HRT regime for BMD treatment.
The study used transdermal E2 replacement (100 μg/day) with cyclic oral progestogen
(10 mg oral medroxyprogesterone acetate daily for 12 days per month). This replacement
therapy improved the BMD of the lumbar spine and of the femoral neck, so that at the
end of the three-year intervention, the BMD did not differ between women with POI
and the control group.31
The treatment of POI can have different doses and dosages according to the life period
of onset of the disease. There is no evidence of which is the best route, oral or
transdermal, and what is the best therapeutic regimen.11
32
33
34
35 In patients diagnosed in the pubertal period and without adequate development of
secondary sexual characteristics, puberty should be induced with a low dose of 17β-estradiol
and a gradual increase over a period of 2 to 3 years. Progestogens should be used
two years after the onset of puberty induction with estradiol or as soon as the first
menstrual bleeding occurs. In cases of later diagnosis, and with no remaining concern
about growth, the initial estrogen dose may be higher and more rapidly progressive
with increases every three to six months until the adult dose is reached. The recommendation
is that the hormonal therapy simulates as close as possible the regular levels of
ovarian estrogen production and its continuity until the natural menopause age.11
21
The use of combined oral contraceptives (COCs) is an alternative to the conventional
treatment with natural estrogens. In cases of adolescents, who are still in the development
phase of the PBM, some studies have shown that COCs may have a less positive impact
on the BMD.36 However, further studies are needed to prove this effect..
A point to consider is the inclusion or not of BMD in the propaedeutic routine of
patients with POI, especially those affected by the disease during adolescence and/or
those with additional risk factors. Although BMD measurement is the gold standard
for bone mass evaluation, and despite the large number of publications clearly pointing
to bone loss, there is no consensus regarding the need to routinely indicate BMD measurement
in the evaluation and follow-up of patients with POI.
According to Cox and Liu,35 “as a consequence of decreased estrogen levels, women
with POI often do not achieve peak bone density and may experience loss of bone mass.
If hormone therapy is initiated and the woman has not experienced fractures, it is
not necessary to do bone mineral density testing.”
On the other hand, other authors indicate BMD examination after the diagnosis of POI.37
38 Torrealday et al39 suggest that BMD measurement may be useful and should be considered
for women with POI already at the beginning of the approach. It should be repeated
in those who decide to continue hormone therapy until the equivalent time of menopause
for that population. In turn, the European Society for Human Reproduction and Embryology
(ESHRE)11 recommends the initial BMD measurement. If the results are normal and the
patient undergoes hormonal therapy immediately upon diagnosis, there is no need to
repeat the measurement. If the BMD measurement indicates osteoporosis, once the HRT
is initiated, the BMD measurement should be repeated after five years. If the BMD
continues to decline even with estrogen therapy, the conduct should be reviewed, and
other factors that trigger osteoporosis should be sought.
The cost-benefit of measuring BMD in osteoporosis screening to assess its benefit
as a prevention method for fractures in women is questioned. Most cohort studies to
assess the use of BMD for this purpose included patients older than 65 years of age.40
For these patients, by considering the cut-off point of 2 standard deviations, the
sensitivity is 9%, the specificity is 99%, and the positive predictive value is 56%.
Therefore, the BMD can predict the risk of fracture, but has low accuracy to identify
individuals who will (or will not) have fractures.41
However, there are currently no alternatives to BMD for this evaluation, since bone
turnover markers do not have well-established reference standards yet, given the variations
observed among the various studies.12
13
14
15
16
17
18
In the Brazilian Unified Health System (SUS, in the Portuguese acronym), BMD measurement
is authorized in some special situations,42 including cases of hypogonadism in men
and women, postmenopausal women with risk factors, and to monitor changes in bone
mass due to the course of osteoporosis and the different treatments available for
this disease. Therefore, there is a possibility of access to the measurement of BMD,
even if using public services, but also practical difficulties to perform the exam
because it has a high cost and, in Brazil, few public services are available to the
population.
Many questions remain unanswered given the lack of scientific evidence:
Are there differences in the behavior of bone mass over time when comparing women
with POI and those who experienced menopause at the natural time?
Can we extrapolate to women with POI the sensitivity, specificity and predictive values
for predicting fractures obtained with the BMD measurement performed in postmenopausal
women?
Is it justified to perform a BMD measurement in young women with POI?
The evidence of the association of hypoestrogenism and low bone density and its association
with the increased risk of fractures could be a justification for dispensing patients
from undergoing a BMD measurement before starting hormone therapy?
It is known that estrogen therapy may fail in some patients, since other factors may
interfere with the maintenance or loss of bone mass. How can we be sure that the patient
undergoing hormone therapy will be protected from bone loss if she is not monitored
through BMD measurements?
Are there alternative ways to confirm that patients with POI are already losing bone
mass without BMD measurements?
Conclusion
In the literature, there are no evidence-based guidelines on criteria to maintain
bone health in women with POI. It has not been definitively demonstrated that a reduced
BMD in POI is indicative of an association of the disease with an increased fracture
risk because the evidence is based on short-term observations and expert opinion.
In fact, studies with the clear aim to clarify this cause-effect relationship are
difficult to perform because they would involve ethical issues (for example, failure
to treat patients on estrogen therapy as a control group), or the high cost and long
duration of the follow-up, since the patients should be observed for long periods.
Moreover, the results of BMD studies performed in postmenopausal women cannot be extrapolated
to a population of young women with estrogen deficiency before the age of 40 years
old in order to predict fractures that will occur 20 to 30 years later, when other
risk factors for fractures may be involved.
Despite the lack of such evidence with long-term randomized clinical trials, common
sense suggests that the physician should rely on existing data in the literature,
especially the guidelines of specialty societies.
The review of the literature shows that the consulted studies are practically consensual
about these aspects of the POI approach. Estrogen replacement therapy should begin
immediately after diagnosis, obviously respecting the contraindications to its use.
The BMD measurement for an initial evaluation before starting hormone therapy would
be a good practice. However, if the patient's access to this test is difficult, she
can be dispensed by considering the unquestionable benefits of estrogens on bone mass,
even in very small doses. The risks of treatment failure should be carefully ascertained
in view of the possibility of associated comorbidities or other factors interfering
with bone mass.
More than half of the women with POI have inadequate vitamin D levels and low calcium
intake. Many are not adherent to hormone therapy, do not exercise regularly, and may
be smokers. Therefore, to ensure good bone mass, in addition to hormone therapy, women
with POI should maintain a healthy lifestyle that involves physical exercise, abstinence
from smoking, a balanced diet with good intake of foods rich in calcium and vitamin
D, and weight control.