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

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

Hypothyroidism:

Hypothyroidism means " Insufficient secretion of thyroid hormones ( T3 and T4 ) by thyroid gland.
Hypothyroidism is a state in which the thyroid gland does not produce a sufficient amount of the thyroid hormones thyroxine (T4) and triiodothyronine (T3).
Iodine deficiency is often cited as the most common cause of hypothyroidism worldwide but it can be caused by many other factors. It can result from the lack of a thyroid gland or from iodine-131 treatment, and can also be associated with increased stress. Severe hypothyroidism in infants can result in cretinism.

Causes Of hypothyroidism:

1. Thyroid Parenchymal defects:

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 pituitary to secrete TSH.


Types Of Hypothyroidism:

There are three types of hypothyroidism.

1. Primary Hypothyroidism:

In primary hypothyroidism, problems lies in thyroid gland itself.
Causes include;

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. problem lies in pituitary gland.

3. Tertiary Hypothyroidism:

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

Clinical Presentation Of Hypothyroidism.

Hypothyroidism is presented clinically in two forms.
a) Cretinism
b) Myxedema

Cretinism:

Hypothyroidism which develops in infancy or early childhood is referred 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 older chlid or an adult is referred 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 edema
11. Enlargement of tongue
12. Deepened voice.