Hypothyroidism - Causes, Types and clinical presentation of Hypothyroidism - Cretinism and Myxedema

Hypothyroidism:

Hypothyroidism means " Insufficient secretion of thyroid hormones ( T3 and T4 ) by the thyroid gland.

Causes Of hypothyroidism:

1. Thyroid Parenchymal defects:
a) A congenital defect in thyroid parenchyma
b) Radiation injury to thyroid parenchyma (e.g radio-iodine, external radiation)
c) Surgical ablation
d) Hashimoto's thyroiditis.

2. Interference with Thyroid hormone synthesis:
a) idiopathic primary hypothyroidism (possibly due to immune blockade of TSH receptors)
b) Heritable biosynthetic defects
c) Iodine deficiency.
d) Drugs (e.g iodides, p-aminosalicylic acid, lithium etc)
e) Hashimoto Thyroiditis

3. Others:
a) Pituitary lesions reducing TSH secretion
b) Hypothalamic lesions that reduce thyrotropin-releasing hormone (TRH) secretion. TRH stimulates the pituitary to secrete TSH.


Types Of Hypothyroidism:

There are three types of hypothyroidism.

1. Primary Hypothyroidism:
In primary hypothyroidism, problems lie in the thyroid gland itself.
Causes include;

a) A congenital defect in thyroid parenchyma

b) Radiation injury to thyroid parenchyma (e.g radio-iodine, external radiation)

                                         c) Surgical ablation

                                         d) Hashimoto's thyroiditis.

2. Secondary Hypothyroidism:

This type of hypothyroidism occurs due to deficient secretion TSH from the pituitary. the problem lies in the pituitary gland.

3. Tertiary Hypothyroidism:

Hypothyroidism due to insufficient secretion of TRH from the hypothalamus is referred to as tertiary hypothyroidism. TRH stimulates TSH secretion by the pituitary which in turn stimulates the thyroid gland to secrete T3 and T4. Deficiency of TRH will ultimately affect the thyroid secretions.

Clinical Presentation Of Hypothyroidism.

Hypothyroidism is presented clinically in two forms.

a) Cretinism

b) Myxedema

1. Cretinism:

Hypothyroidism which develops in infancy or early childhood is referred to as cretinism. 

Causes:

1. Iodine deficiency

2. Enzyme deficiency (which is very rare) 

Clinical Features:

1. Mental retardation,

2. Short Stature

3. Coarse facial features

4. Protruding tongue

5. Umbilical hernia.

Myxedema:

Hypothyroidism developing in an older child or an adult is referred to as Myxedema.

Clinical Features.

1. Generalized fatigue

2. Mental sluggishness

3. Slow speech

4. Cold intolerance.

5. Overweight

6. Shortness of breath 

7. Constipation 

8. Decreased sweating

9. Cool and pale skin

10. Generalized oedema

11. Enlargement of tongue

12. Deepened voice.