Subclinical hypothyroidism
notes by dr Claudio Italiano
Usually the internist comes across more easily in cases of subclinical
hypothyroidism more than in patients with frank or overt hypothyroidism, so to
speak to those patients with raspy, stridula, bradykerichism,
hypercholesterolemia, obesity, asthenia and so on. It is a dangerous condition
in the pregnant, which must be corrected with adequate endocrinological control.
Dimension of the problem
Literature data give a prevalence of 5% in women and 3% in men that increases
with age. On the other hand, subclinical hypothyroidism is defined by the
increase of TSH> 10 μU / ml with fT4 and fT3 in the norm, with no clinical
symptoms. Patients with subclinical hypothyroidism have normal levels of T4 and
elevated levels of TSH and are clinically euthyroid by definition. The increase
in levels in the circulation of TSH reflects the effects of small reductions in
thyroid secretion. These reductions can be caused by any of the causes of
hypothyroidism; the most frequent causes are:
chronic autoimmune thyroiditis, previous radioiodine therapy due to the presence
of thyrotoxicosis and iodine deficiency.
The recommendations if they agree in recommending screening in the population
with the highest prevalence of tire diseases, on the usefulness of a screening
on the general population there is no agreement:
· All adults aged 35 years and over every 5 years in the absence of symptoms or
risk factors, otherwise with higher frequencies (Am. Thyroid Association)
· Maintain a high clinical surveillance and a high index of suspicion in
menopausal women and within 6 weeks after delivery (The Canadian Task Force).
· All women after age 50 (Am. College of Physician)
· Men and women after 60 (Am Academie of Family Physician)
· In most cases, subclinical hypothyroidism remains stable over time (70-80% at
10 years),
· In a small percentage it can regress
· But in variable percentages it evolves towards overt hypothyroidism. And this
evolution is more frequent in autoimmune forms (AbTPO positives)
Causes of subclinical hypothyroidism
· The primary cause is autoimmune thyroid disease,
· Previous radioiodine therapy
· Iatrogenic causes:
- overdose antithyroid drugs
- Lithium,
- Amiodarone (treatment of arrhythmias)
- Alpha interferon
Population at risk to be monitored for
hypothyroidism
· In the setting of General Medicine it seems reasonable to propose to
identify a population at greater risk in which to have a greater surveillance:
· Down Syndrome patients
· Women in post-partum (within 6 months)
· Menopausal women
· Patients with hypercholesterolemia, especially if not sensitive to diet
· Patients with FA or heart failure
· Patients familiar with thyropathy, especially if women
· Patients with other autoimmune diseases (vitiligo ...)
· Elderly patients
· Patients with type 1 diabetes mellitus
Some of these patients have a thyroid enlargement and may report some
nonspecific symptoms characteristic of hypothyroidism, such as fatigue and loss
of strength. They may also show a slight increase in serum concentrations of LDL
cholesterol and creatine kinase, a reduction in cardiac contractility and
hearing.
Symptoms
In general, subclinical hypothyroidism is associated with particular signs, but
if some symptoms of frank hypothyroidism may be present, there is no proven link
between subclinical hypothyroidism and obesity, depression or cognitive deficits
and asthenia is a symptom very nonspecific that it is difficult to attribute to
the partial deficiency of thyroid hormone
There are many situations that are due to a lack of thyroid hormone:
weight gain,
depression,
cognitive impairment in the elderly,
asthenia
Diagnosis of subclinical hypothyroidism
As a first screening it requires the dosage of the thyroid hormones fT3, fT4 and
TSH. Even in the case of altered TSH in asymptomatic patients, a time interval
between TSH dose and diagnostic completion does not lead to changes in
management
· REPEAT THE DOSAGE OF THERRO-TOXOPHYDRATE HARDENER antibodies (AbTPO): even if
their title changes this has no clinical significance, dosage of anti-microsomal
antibodies, and antibodies against thyroglobulin. The anti-TPO and
anti-microsomal antibodies are the same and anti-thyroglobulin antibodies serve
only in special situations (when the dosage of Tireoglobulin is used for the
follow up of differentiated carcinomas to highlight false negatives)
If hypothyroidism is confirmed, the request for a thyroid ultrasound is
appropriate: ultrasound may be normal. More often, it has an echographic pattern
typical of chronic autoimmune thyroiditis with presence of fibrous septa,
pseudonodules and hyperechogenic nodular areas. These nodules do not require
cytological diagnosis on needle aspiration
Treatment of patients with subclinical hypothyroidism
It is the subject of controversy. It is not necessary to prevent the appearance
of a clinically manifest hypothyroidism, as this progression is inevitable and
is very slow (equal to 5-20% per year). The treatment can reduce the enlargement
of the thyroid and the nuanced symptoms if they are present. In controlled
studies conducted in patients undergoing T4 therapy, these symptoms improved
more during treatment with Ti compared to placebo treatment, and the same
occurred for cardiac contractility in another study, while changes in
cholesterol concentrations were minimal. These results show how T4 therapy is
useful in the case of subclinical hypothyroidism characterized by enlargement of
the gland (see goiter) and non-specific symptoms. However, attention must be
paid to the fact that L-tyloxin overdoses that suppress TSH (iatrogenic
subclinical hyperthyroidism) have been associated with increased frequency of AF
in subjects> 60 years (28% vs. 11% with normal TSH values); moreover, bone mass
can be reduced in post-menopausal women.
When to always treat?
Basic subclinical hypothyroidism requires no therapy, except:
· PREGNANT
· When hyperlipidemia non-sensitive to diet coexists
· When there is a history of heart failure,
· When there are signs and symptoms suggestive of hypothyroidism (ex iuvantibus)
· Therapy should be monitored to avoid overdosing with TSH and fT4
Link on topic
La Tiroide: parte introduttiva
il gozzo semplice, parte introduttiva
il gozzo semplice, trattamento
La Tiroide: funzione della tiroide,
parte introduttiva
La Tiroide: FT3, FT4, TSH, TESTS
di funzionalitą
La tiroide, l'ipotiroidismo
Le condizioni di deficit di ormone
tiroideo
La visita del paziente con il gozzo
I noduli tiroidei, caldi e freddi.
I noduli tiroidei: la diagnostica
previo agoaspirato.
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