Thyroid

Question 1

At the age of 21, Ms Pillay was investigated for primary amenorrhoea. She mentioned feeling extremely lethargic and depressed with decreased libido. Thyroid function testing was performed and thyroid stimulating hormone was found to be elevated. Subsequently treated with eltroxin (thyroid hormone) which normalised her menses.

State the likely diagnosis (½)

Answer 1

Primary hypothyroidism

Question 2

Outline the mechanism for amenorrhoea in Ms Pillay (2)

Answer 2

Prolactin is elevated, which suppresses the pulsatile release of gonadotropin-releasing hormone. Prolactin secretion is stimulated by thyrotropin-releasing hormone which is increased in response to the low thyroid hormone levels.

Question 3

Explain the amenorrhoea in primary hypothyroidism (4)

Answer 3

Decreased T4 lifts negative feedback, resulting in increased thyrotropin releasing hormone [1], which in turn, increases prolactin secretion [1]. Prolactin inhibits the pulsatile secretion of gonadotropin releasing hormone [1], resulting in decreased luteinising hormone and follicle stimulating hormone [1].

Question 4

Briefly outline the mechanism by which primary hypothyroidism (i.e. decreased thyroid hormone production) causes amenorrhoea (3)

Answer 4

inhibition of TRH is lifted  therefore increased production of prolactin  suppresses pulsatility of GnRH secretion

Question 5

List three (3) other causes of amenorrhoea caused by the mechanism in question above (3x½ = 1½)

Answer 5

Dopamine antagonists, Prolactinoma, Pregnancy, Lactation, “Stalk effect”

Question 6

List four (4) other endocrine causes of amenorrhoea (excluding pregnancy) (4x½ = 2)

Answer 6

Primary ovarian failure; polycystic ovarian syndrome; prolactinoma; hypopituitarism; hypothalamic disease; androgen producing tumour; hyperthyroidism.

Question 7

State the expected direction of change in the thyroid stimulating hormone and thyroxine levels after treatment (2x½ =1)

Answer 7

TSH increased; T4 decreased

Question 8

Name the two (2) most well described clinical complications of subclinical hyperthyroidism.

Answer 8

Atrial fibrillation

Loss of bone density

Question 9

Patients with primary hypothyroidism typically present with a low T3/T4 and a high TSH. List two (2) other biochemical features associated with this condition.

Answer 9

Increased prolactin
Increased cholesterol
Increased CK