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.Tiroide, disegno stilizzato per la localizzazione tiroidea

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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