Page 819 - Textbook of Pathology, 6th Edition

nervousness, palpitation, fatigue, weight loss in spite of good 1. Developmental anomalies e.g. thyroid agenesis and ectopic 803
appetite, heat intolerance, perspiration, menstrual thyroid.
disturbances and fine tremors of the outstretched hands. 2. Genetic defect in thyroid hormone synthesis e.g. defect in
Cardiac manifestations in the form of tachycardia, iodine trapping, oxidation, iodination, coupling and
palpitations and cardiomegaly are invariably present in thyroglobulin synthesis.
hyperthyroidism. The skin of these patients is warm, moist 3. Foetal exposure to iodides and antithyroid drugs.
and flushed. Weakness of skeletal muscles and osteoporosis 4. Endemic cretinism in regions with endemic goitre due to
are common. Typical eye changes in the form of exoph- dietary lack of iodine (sporadic cretinism, on the other hand,
thalmos are a common feature in Graves’ disease. Serum is due to developmental anomalies and genetic defects in
levels of T and T are elevated but TSH secretion is usually thyroid hormone synthesis described above).
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4
inhibited. CLINICAL FEATURES. The clinical manifestations usually
A sudden spurt in the severity of hyperthyroidism termed become evident within a few weeks to months of birth. The
‘thyroid storm’ or ‘thyroid crisis’ may occur in patients who presenting features of a cretin are: slow to thrive, poor
have undergone subtotal thyroidectomy before adequate feeding, constipation, dry scaly skin, hoarse cry and
control of hyperthyroid state, or in a hyperthyroid patient bradycardia. As the child ages, clinical picture of fully-
under acute stress, trauma, and with severe infection. These developed cretinism emerges characterised by impaired
patients develop high grade fever, tachycardia, cardiac skeletal growth and consequent dwarfism, round face,
arrhythmias and coma and may die of congestive heart narrow forehead, widely-set eyes, flat and broad nose, big
failure or hyperpyrexia. protuberant tongue and protuberant abdomen. Neurological
features such as deaf-mutism, spasticity and mental
HYPOTHYROIDISM deficiency are more evident in sporadic cretinism due to
developmental anomalies and dyshormonogenetic defects.
Hypothyroidism is a hypometabolic clinical state resulting
from inadequate production of thyroid hormones for Characteristic laboratory findings include a rise in TSH
prolonged periods, or rarely, from resistance of the peripheral level and fall in T and T levels.
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3
tissues to the effects of thyroid hormones. The clinical
manifestations of hypothyroidism, depending upon the age Myxoedema CHAPTER 27
at onset of disorder, are divided into 2 forms: The adult-onset severe hypothyroidism causes myxoedema.
1. Cretinism or congenital hypothyroidism is the development The term myxoedema connotes non-pitting oedema due to
of severe hypothyroidism during infancy and childhood. accumulation of hydrophilic mucopolysaccharides in the
2. Myxoedema is the adulthood hypothyroidism. ground substance of dermis and other tissues.
Cretinism ETIOPATHOGENESIS. There are several causes of
myxoedema listed below but the first two are the most
A cretin is a child with severe hypothyroidism present at common causes:
birth or developing within first two years of postnatal life. 1. Ablation of the thyroid by surgery or radiation.
This is the period when brain development is taking place; 2. Autoimmune (lymphocytic) thyroiditis (termed primary The Endocrine System
in the absence of treatment the child is both physically and idiopathic myxoedema).
mentally retarded. The word ‘Cretin’ is derived from the 3. Endemic or sporadic goitre.
French, meaning Christ-like because these children are so 4. Hypothalamic-pituitary lesions.
mentally retarded that they are incapable of committing sins. 5. Thyroid cancer.
ETIOPATHOGENESIS. The causes of congenital 6. Prolonged administration of antithyroid drugs.
hypothyroidism are as follows: 7. Mild developmental anomalies and dyshormonogenesis.

Figure 27.6 Appearance in functional disorders of the thyroid gland.