30. TYPICAL FORMS OF PATHOLOGY OF THE THYROID GLAND AND PARATHYROID GLANDS

Pathology of the thyroid gland is manifested by qualitative or quantitative alterations in hormone secretion, enlargement of the thyroid or both. Insufficient hormone secretion results in hypothyroidism or myxedema, in which hypometabolism is a principal feature. Conversely, the excessive secretion of hormone results in hypermetabolism and other features, together termed thyrotoxicosis. Enlargement of the thyroid gland may be generalized or focal. Goiters may be associated with increased, normal or decreased hormone secretion.

HYPOTHYROIDISM

Hypothyroidism results from abnormalities that lead to insufficient synthesis of thyroid hormone. Hypothyroidism dating from birth and resulting in developmental abnormalities is termed cretinism.

The term «myxedema» designates severe hypothyroidism in which there is accumulation of hydrophylic mucopolysaccharides in the dermis and other tissues, leading to thikening of the facial features and doughy induration of the skin.

Etiology and pathogenesis

The primary thyroid varieties account for the majority of cases, and only about 5% being suprathyroid in origin.

Causes of primary hypothyroidism

Hypothyroidism resulting from functional insufficiency of the thyroid gland:

•  deficit of iodine in drinking water and meal;

•  goitrogenic agents (thyocyanates);

•  congenital deficit of enzymes of the T₃ and T₄ synthesis pathway;

•  Wolf-Chaikoff phenomenon.

Thyroprivic hypothyroidism due to loss of parenchyma of the thyroid gland:

•  thyroiditis (Hashimoto's thyroiditis, etc.);

•  congenital hypoplasia of the thyroid gland;

•  radioactive or surgical ablation of the thyroid gland.