DISEASES OF THYROID GLAND
Thyroid gland is located below and in front of larynx, consists of two bulky lateral lobes. The lobes are divided into lobules composed of about 20 to 40 evenly dispersed follicles which are filled with thyroglobulin.
TSH (thyrotropin) is released by thyrotroph cells in the anterior pituitary gland . TSH binds to its receptor on the thyroid follicle and results in growth of thyroid gland and thyroid hormone synthesis and release.
• Hyperthyroidism (thyrotoxicosis): Excessive production of thyroid hormone by the thyroid gland
• Hypothyroidism : disorder where thyroid gland doesnot produce enough thyroid hormones (Thyroxine and T3)
• Enlargement of the thyroid (goitre or thyroid nodule).
1. Causes of hyperthyroidism (for details see disease below)
a. Graves’ disease 76%
b. Multinodular goitre 14%
c. Solitary thyroid adenoma 5%
d. Thyroiditis 3-4% (leads to inflammation of thyroid follicle and release of colloid in blood) this is temporary condition
e. Iodide-induced (Associated with increasednIodine Uptake)
i. Drugs (amiodarone)
ii. Radiographic contrast media
iii. Iodine prophylaxis programme (in areas where there is iodine deficiency)
f. Extrathyroidal source of thyroid hormone
i. Factitious thyrotoxicosis (due to overdose of thyroxine hormone)
i. TSH-secreting pituitary adenoma
ii. Follicular carcinoma
2. Clinical signs and symptoms
a. Weight loss despite normal or increased appetite
b. Heat intolerance, sweating
g. Irritability, emotional lability
h. Palmar erythema
i. Sinus tachycardia
j. Lid retraction,
k. lid lag
This is the most common cause of Grave’s disease.
Affects the age group of 30-50
It results from the production of IgG antibodies directed agsinst the TSH receptor on the thyroid follicular cells. This leads to increased thyroid hormones (T3 and T4) as well as thyroid enlargement.
It is distinguished from other types of hyperthyroidism by the presence of:
a) Thyroid enlargement: This occurs due to hyperactivity induced by IgG. Gland is enlarged 2-3 times.
b) Ophthalmopathy: It occurs due to exophthalmus and lid retraction. There is excessive lacrymation associated with conjunctivitis and corneal ulceration.
c) Peritibial myxedema: Grave’s disease is associated with excessive synthesis and release of mucopolysaccharides. Its accumulation causes dermopathy with raised pink or purplish plaque on
the front side of the legs.
TOXIC FOLLICULAR ADENOMA
• The adenoma of follicle leads to autonomous secretion of excess thyroid hormone and inhibits TSH secretion.
• This ultimately leads to high T3 and T4 levels and atrophy of normal follicles.
• It is sometimes automatically resolved due to infarct formation.
DIAGNOSIS OF HYPERTHYROIDISM
• Free T3 level (increased)
• Free T4 level (increased)
• TSH level (some times low/ generally not detected in hyperthyroidism patient)
If the T3 and T4 level are normal and TSH level is reduced, the condition is known as Sub-clinical hyperthyroidism.