Hypothyroidism/A common thyroid hormone abnormality/causes of hypothyroidism/sign/symptoms/feature/blood test for hypothyroidism/treatment/Thyroxine dose/treatment of hypothyroidism in pregnancy

 Hypothyroidism/A common thyroid hormone abnormality

Etiology/causes

I. Congenital-

Agenesis

II. Post-surgery

IlI. Post-irradiation

    Radioactive iodine therapy

    External neck irradiation

IV. Defects of hormone synthesis

    lodine deficiency

   Dyshormonogenesis

   Antithyroid drugs

   Other drugs (e.g. lithium, amiodarone,

    interferon)

V. Infiltration

     Tumour

VI. Secondary (to hypothalamic-pituitary,

Autoimmune disease)

    Atrophic thyroiditis

     Hashimoto's thyroiditis

    Postpartum thyroiitis

Epidemiology

• Prevalence :

 2% in women, but <0.1% in

men (uk data)

Lifetime prevalence for an individual is

higher - perhaps as high as 9% for

women and 1% for men The worldwide

prevalence of subclinical

hypothyroidism varies from 1% to 10%.

Clinical features

Symptoms

1. Weight gain

2. Cold intolerance

3. Fatigue, somnolence

4. Dry skin

5. Dry hair

6. Menorrhagia

Less common

7. Constipation

8. Hoarseness

9. Carpal tunnel syndrome

10. Alopecia

11. Bodyache

12. Arthralgia

13. Muscle stiffness 

14. Depression

15. Infertility

Signs

1. Weight gain

Less common

2. Puffy face

3. Periorbital oedema

4. Loss of lateral eyebrows

5. Anaemia

6. Bradycardia

7. Hypertension

8. Delayed relaxation of reflexes

9. Myxoedema (non pitting oedema)

Rare

10. Ascites

11. Pericardial and pleural effusions 

Investigations/blood test

 => increased TSH (usually in excess of 20 mU/L)

and decreased T4

>Serum T3 is unhelpful.

Others Non-specific

• Hypercholesterolaemia

• Anaemia: normochromic

normocytic/macrocytic/ microcytic (in

women, due to menorrhagia)

• decreased Na (Hyponatraemia)

• increased Creatinine Clearance

• increased AST /SGOT

• ↑LDH

Management of hypothyroidism

• If there is no residual thyroid function,

the daily replacenment dose of

Thyroxine/Levothyroxine Sodium is

usually 6 mcg/kg body weight (typically

100-150 mcg).

• Adult patients under 60 without evidence

of heart disease may be started on 50-

100 mcg levothyroxine (T4) daily,

increasing after 2-4 weeks. (at first even

without measuring hormone level)

• People with ischaemic heart disease

require even lower initial doses. Start

with 25 g daily and perform serial ECGs

• The dose is adjusted on the basis of

TSH levels, with

the goal of treatment being a normal

TSH, ideally in the lower half of the

reference range.

• TSH responses are gradual and should

be measured about two months after

instituting treatment or after any

subsequent change in levothyroxine

dosage. Ideally the tests should be

repeated at 6-8 weeks intervals.

• The clinical effects of levothyroxine

replacement are slow to appear.

Patients may not experience full relief

from symptoms until 3-6 months after

normal TSH levels are restored.

• Adjustment of levothyroxine dosage is

made in 12.5- or 25 mcg increments if

the TSH is high; decrements of the same

magnitude should be made if the TSH is

suppressed.

• The uSual maintenance dose is 100-150

Pg given as a single daily dose.

• Once full replacement is achieved and

TSH levels are stable , follow-up

measurement of TSH is recommended

at annual intervals and may be extended

to every 2-3 years if a normal TSH is

maintained over several years.

• Treatment is required for life. (Except

transient hypothyroidism)

• It is important to ensure ongoing

adherence, however, as patients do not

feel any symptomatic difference after

missing a few doses of levothyroxine,

and this sometimes leads to self-

discontinuation.

• Patients with a suppressed TSH of any

cause, including T4 oVertreatment, have

an increased risk of atrial fibrillation

and reduced bone density.

• Causes of increased levothyroxine

requirements are-

       • malabsorption

        • estrogen therapy

       • drugs that interfere with T4

      absorption or clearance such as

               cholestyramine,

               ferrous sulfate,

              calcium supplements,

              aluminum hydroxide

              rifampicin

              amiodarone

             carbamazepine

              phenytoin

             proton pump inhibator

in pregnancy.

During pregnancy, an increase

inThyroxine/Levothyroxine Sodium

dosage of about 25-50 ug is often 

dosage of about 25-50 ug is often

needed to maintain normal TSH levels.

• Serum TSH and free T4 should be

measured during each trimester and the

dose of levothyroxine adjusted to

maintain a normal TSH.

Caution:

Inadequate therapy may be associated with

impaired cognitive development in an unborn child.