HYPOTHYROIDISM ( HASHIMOTO'S THYROIDITIS)

HYPOTHYROIDISM

Is defined as a decrease of thyroxine (T4) and increase of Thyroid stimulatin hormone (TSH), accompanied by certain symptoms.

CONGENITAL HYPOTHYROIDISM

Occurs in about 1/4000 newborns, but is only diagnosed in 10% of them. As well as there are increase of TSH and T4 decrease, the main symptoms include: umbilical hernia, hypotonia, nutrional feeding problems, jaundice, enlarged of the tongue and delayed bone maturation.

AUTOIMMUNE HYPOTHYROIDISM

There are two phases: Hashimoto's thyroiditis and the atrophic thyroiditis. In the first, there are limphocityc infiltrate, a little fibrosis and coloid decrease. In the last one, there are no coloid, much fibrosis and less lymphocytic infiltrate. Is caused by auto-antibodies against Thyroperoxidase (TPO), Thyroglobuline (Tg) and TSH receptor (TSH-R). There are many evidences too, of genetic factor that may contribute to the disease, like HLA-DR and CTLA-4 mutations that can be predisposing for develope hashimoto's thyroiditis. The rubella infection is a well documented factor that can ellicit the disease, as well as the iodine excess like a risk factor.

About antibodies, TPO and Tg are in major patients and works like autoimmune markers, but can exist TSH-R antibodies that block the TSH link to receptor and ellicit hypothyrodism in 10% of patients. Rarely, can coexist TSH-R antibodies and TSI (Grave's antibodies) that bring a fluctuating situation for the patient, between hyper and hypothyroidism. Something important is that TPO and Tg antibodies don't cross the placenta, so they are not going to cause damage in the fetal thyroid. The principal warning for women who is planning be pregnant is to control her disease beacause there is a high risk for mental retard in children.

Clinical features

SYMPTOMS
The main symptoms of hypothyroidism include: weakness, tiredness, hair loss, cold sensation, hoarse voice, dispnea, constipation, weight gain despite loss of apetite, dificulty concentrating, menhorragia, paresthesia, conductive deafness, dry skin, libido lost.

SIGNS
peripheral edema, mixedema, dry skin, hair loss, nail weak, carpal tunel syndrome, serosity cavity effusions, retarded relax phase usually in the aquilian reflex, cold extremities, madarosis, heterogenous goiter.

Diagnose

The diagnose is usually performed with the hormone values mentioned above, clinical symptoms and TPO Ab + (which are positive in 90%). If there still doubt, it can proceed with FNA (fine needle aspiration) biopsy to confirm the diagnose.

Treatment

The indicated treatment is levothyroxine 1.6g/ Kg of body weight if there is no remanent of thyroid tissue. Aproximately, 100-150mg daily. If there is still thyroid tissue (e.g. graves) is recomended start with lower doses (75-125mg). The goal is reduce TSH to normal levels; this can take 3-6 months aproximately, so is very important to explain it to avoid adherence treatment lost.

Complications

Pseudotumor cerebri in children for prolonged use of levothyroxine but is too rare. Mixedema coma, is a coma induce by a crisis in which there are seizures, apnea and the patient can die, this is a very unusual complication.

SUBLINICAL HYPOTHYROIDISM

Is defined as hormones decrease but with no symptoms added. The indication of treatment is a TSH above 10mU/L, and star with only 25/50 mg. If there is TPO Ab+, the patient is in high risk of develope a overt hypothyroidism.

Another hypothyroidisms: Iatrogenic (e.g. after a thyroidectomy), excessive radioactive I therapy

References: Harrison, Internal medicine, 17 Edition.