SN1 SHORT NOTE 5M ★ High-yield

Write a short note on hypothyroidism. Describe cretinism and myxoedema.

Physiology · 1st Professional — Pre-Clinical

Definition

Hypothyroidism = a clinical state resulting from deficient secretion or action of thyroid hormones.Cretinism — in infancy and childhood. Myxoedema — in the adult.

Causes

Iodine deficiency — the commonest cause worldwide
Hashimoto thyroiditis — autoimmune; the commonest cause where iodine is sufficient
Post-surgical, post-radioiodine
Antithyroid drugs, lithium, amiodarone
Secondary — pituitary or hypothalamic failure (TSH low)
Congenital — thyroid agenesis, dyshormonogenesis

Cretinism

Feature	Detail
Growth	Dwarfism with disproportionate body — short limbs relative to trunk
CNS	Mental retardation — irreversible if untreated
Face	Puffy, coarse features; protruding tongue; flat broad nose
Abdomen	Pot belly with umbilical hernia
Other	Feeding difficulty, constipation, hoarse cry, prolonged neonatal jaundice, delayed bone age

CLINICAL PEARL

Note: treatment must begin within the first few weeks of life to prevent permanent mental retardation. Hence neonatal TSH screening.

Myxoedema (adult)

General — weight gain despite poor appetite, cold intolerance, lethargy, slow speech and thought
Skin — dry, coarse; non-pitting oedema from mucopolysaccharide deposition; puffy face; loss of the outer third of the eyebrows
CVS — bradycardia, low voltage ECG, pericardial effusion, ↑ cholesterol → accelerated atherosclerosis
Neuromuscular — delayed relaxation of ankle jerk (the classical sign), muscle cramps, carpal tunnel syndrome
Reproductive — menorrhagia, infertility
Myxoedema coma — hypothermia, bradycardia, hypoventilation; mortality is high

Investigations

Type	TSH	Free T4
Primary hypothyroidism	↑↑	↓
Subclinical	↑	Normal
Secondary (pituitary)	↓ or normal	↓

TSH is the single most sensitive test for primary disease
Anti-TPO antibodies confirm Hashimoto thyroiditis

Applied Aspects

Treatment — oral levothyroxine, once daily on an empty stomach; dose titrated against TSH
Start low in the elderly and in ischaemic heart disease — a rapid rise in metabolic rate may precipitate angina or infarction
Universal salt iodisation has greatly reduced endemic cretinism in India

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