Hypothyroidism

1. HYPOTHYROIDISM
Prof. Dr. C. Hariharan.
M2.

2. THE THYROID GLAND
• It secretes predominantly thyroxine (T4) and only a small amount of
triiodothyronine (T3); approximately 85% of T3 in blood is produced
from T4 by a family of monodeiodinase enzymes.
• Production of T3 and T4 in the thyroid is stimulated by thyrotrophin
(TSH), a glycoprotein released from the thyrotroph cells of the
anterior pituitary in response to the hypothalamic thyrotrophin-
releasing hormone (TRH).

3. HYPOTHYROIDISM
• Women are affected approximately six times more frequently than
men.

5. • A consequence of prolonged hypothyroidism is the infiltration of
many body tissues by the mucopolysaccharides, hyaluronic acid and
chondroitin sulphate, resulting in a low-pitched voice, poor hearing,
slurred speech due to a large tongue, and compression of the median
nerve at the wrist (carpal tunnel syndrome). Infiltration of the dermis
gives rise to nonpitting oedema (myxedema).

6. Signs and Symptoms:
• Common: Weight gain, Cold intolerance, Fatigue, Somnolence, Dry
skin, Menorrhagia.
• Less Common: Constipation, Hoarseness, Carpal tunnel syndrome,
Alopecia, Aches and pains, Muscle stiffness, Deafness, Depression,
Anaemia, Dermal myxoedema, Infertility.
• Rare: Psychosis (myxoedema madness), Galactorrhoea, Impotence,
Ileus, ascites, Pericardial and pleural effusions, Cerebellar ataxia,
Myotonia.

7. Investigations:
• Serum T4 is low and TSH is elevated, usually in excess of 20 mU/L.
Measurements of serum T3 are unhelpful since they do not
discriminate reliably between euthyroidism and hypothyroidism.
• Secondary hypothyroidism is rare and is caused by failure of TSH
secretion in an individual with hypothalamic or anterior pituitary
disease.
• In prolonged hypothyroidism, the ECG demonstrates sinus
bradycardia with low-voltage complexes and ST segment and T-wave
abnormalities.
• Measurement of thyroid peroxidase antibodies can also be helpful.

8. Non specific laboratory abnormalities:
• Serum enzymes: raisedcreatine kinase, aspartate aminotransferase,
lactate dehydrogenase (LDH).
• Hypercholesterolaemia.
• Anaemia: normochromic normocytic or macrocytic.
• Hyponatraemia.

9. Management:
• Treatment is with levothyroxine replacement.
• It is customary to start with a low dose of 50 µg per day for 3 weeks,
increasing thereafter to 100 µg per day for a further 3 weeks and
finally to a maintenance dose of 100–150 µg per day.
• Levothyroxine has a half-life of 7 days so it should always be taken as
a single daily dose and at least 6 weeks should pass before repeating
thyroid function tests and adjusting the dose, usually by 25 µg per
day.
• Levothyroxine absorption is maximal when the medication is taken
before bed and may be further optimised by taking a vitamin C
supplement.

10. Hypothyroidism in pregnancy:
• Most pregnant women with primary hypothyroidism require an
increase in the dose of levothyroxine of approximately 25–50 µg daily
to maintain normal TSH levels to avoid cognitive impairment in the
foetus.
• This may reflect increased metabolism of thyroxine by the placenta
and increased serum thyroxine binding globulin during pregnancy.

11. Myxoedema Coma:
• It is a rare presentation of hypothyroidism in which there is a
depressed level of consciousness, usually in an elderly patient.
• Body temperature may be as low as 25°C, convulsions are not
uncommon and CSF pressure and protein content are raised.
• It is a medical emergency and suspected cases should be treated with
an intravenous injection of 20 µg triiodothyronine, followed by
further injections of 20 µg 3 times daily until there is sustained clinical
improvement.

12. THANK YOU.