3. Thyroid hyperplasia

Question 1

Types of thyroid hyperplasia

Answer 1

1. Simple goitre

2. Multinodular goitre

Question 2

Definition of thyroid hyperplasia

Answer 2

Non-neoplastic proliferative growth of the thyroid gland

Question 3

Definition of simple goitre

Answer 3

Diffuse non-toxic enlargement of the thyroid gland

Question 4

Causes of Simple Goitre

Answer 4

1. Endemic goitre
   - Low iodine levels in soil, water & food supply (endemic goiter)
   - Ingestion of goitrogens (substances that interfere with thyroid hormone synthesis)
   i. Vegetables belonging to the Cruciferae family (cabbage, cauliflower, Brussel sprouts, turnips)
2. Sporadic goitre
   - Dyshormonogenetic goiter (due to AR inherited defects in enzymes for thyroid hormone synthesis)
   - Idiopathic

Question 5

Pathogenesis of simple goitre

Answer 5

1. Impaired thyroid hormone synthesis results in lowered circulating thyroid hormone levels, which increased thyroid stimulation hormone (TSH) production by the anterior pituitary
2. Increased TSH levels act on the thyroid gland to cause hypertrophy & hyperplasia of follicular cells
   - Results in compensatory diffuse increase in functional thyroid mass
   - Allows overcoming of original thyroid hormone deficiency , hence simple goitres are euthyroid

Question 6

Morphology of simple goitre

Answer 6

1. Hyperplastic stage
   - Diffuse mild enlargement
   - Crowded columnar cells forming pseudopapillae (also seen in multinodular goitre & Graves)
2. Colloid involution stage
   - Flattened cuboidal epithelium
   - Abundant colloid (brown glassy cut surface - normal appearance of thyroid colloid)

Question 7

Clinical features of simple goitre

Answer 7

1. Diffuse enlargement of thyroid gland without nodularity
2. Laboratory test
   - Normal free T3 & T4, slightly elevated/normal TSH
3. Mass effects
   - Airway obstruction, dysphagia, SVC syndrome
4. May induce cretinism in infants & young children

Question 8

Definition of Multinodular Goitre

Answer 8

Irregular enlargement of thyroid as a progression from simple goitre

Question 9

Pathogenesis of multinodular goitre

Answer 9

Recurrent episodes of hyperplasia (simple goitre) & involution produces a more irregular enlargement of the thyroid gland

Question 10

Morphology of multinodular goitre

Answer 10

1. [Grossly]
   - Multilobulated asymmetrical enlargement (if it grows behind the sternum & clavicle → intrathoracic/plunging goitre)
   - Cut section: brown gelatinous colloid, hemorrhage, cystic change
2. [Histologically]
   - Colloid-rich follicles lined by crowded columnar cells, giving rise to pseudopapillae appearance (also seen in simple goitre & Graves)
   - Lacks fibrous capsule (important to note as this distinguishes multinodular goitre from follicular adenomas & carcinomas which have a capsule demarcating hyperplastic follicles from the residual normal parenchyma)

Question 11

Clinical features of multinodular goitre

Answer 11

1. Asymmetrical nodular enlargement of thyroid gland often with a dominant palpable nodule present
   - Mimics thyroid carcinoma
2. Laboratory test
   - Normal free T3 & T4, slightly elevated/normal TSH
3. Mass effects
   - Airway obstruction, dysphagia, SVC syndrome
4. Toxic multinodular goitre (Plummer Syndrome)
   - Development of an autonomous nodule within a longstanding multinodular goitre which produces hyperthyroidism