Thyroid

Question 1

Thyroid physiology

Answer 1

Hypothalamus secretes thyrotropin-releasing hormone (TRH), a tripeptide, that stimulates production of thyroid-stimulating hormone (TSH), a glycoprotein, from the anterior pituitary.
TSH increases production and release of T4 and T3 from the thyroid, which exert -ve feedback on TSH production.
Most T3 and T4 in plasma is protein bound, thyroxine-binding globulin (TBG).

Question 2

Increased TSH and Decreased T4

Answer 2

Hypothyroidism

Question 3

Increased TSH, normal T4

Answer 3

Treated hypothyroidism or subclinical hypothyroidism

Question 4

Increased TSH, Increased T4

Answer 4

TSH secreting tumour or thyroid hormone resistance

Question 5

Decreased TSH, Increased T4 or T3

Answer 5

Hyperthyroidism

Question 6

Decreased TSH, normal T4 / T3

Answer 6

Subclinical hyperthyroidism

Question 7

Decreased TSH, Decreased T4

Answer 7

Central hypothyroidism

Question 8

Decreased TSH, T4 and T3

Answer 8

Sick euthyroidism or pituitary disease

Question 9

Multiple methods of TSH activation

Answer 9

1. Normal TSH secreting adenoma
2. Graves’ disease
3. Non autoimmune hyperthyroidism (Genetic)

Question 10

Thyroid auto-antigen (TSHR)

Answer 10

Chromosome 14, G-protein receptor, receptor for TSH. Used for testing for Graves’ disease.

Question 11

Auto-antigen thyroid peroxidase (TPO)

Answer 11

Chromosome 2, Haem enzyme, Used clinically in Hashimoto’s disease

Question 12

Iodine in thyroid

Answer 12

Clinical consequences of reduced iodine.

1. Newborn = increased mortality, cretinism, psycho motor deficits.
2. Neonates, Infants and adults = Goitre and hypothyroidism (also in infants can retard growth)

Question 13

Side effects of iodine

Answer 13

Iodine induces Hyperthyroidism, hypothyroidism, thyroiditis, modulation thyroid cancer

Question 14

Causes of hyperthyroidism

Answer 14

1. Graves’ disease
2. Toxic multinodular goitre
3. Toxic adenoma
4. Thyroiditis - subacute, postpartum
5. Drug induced - lithium, amiodarone
6. TSH producing pituitary adenoma
   7 etc

Question 15

Treatment of hyperthyroidism

Answer 15

1. Drugs (Carbimazole, Propylthiouracil, propanolol, steriods, lithium)
2. Radioiodine therapy

Question 16

Carbimazole

Answer 16

Prodrug converted to active form methimazole, prevents TPO enzyme coupling and iodising thyrosine residues of thyroglobin - thus reducing production of T3 and T4

SE: Skin rashes, agranulocytosis, pancreatitis, cholestatic jaundice, hepatitis, lymphadenopathy, thrombocytopenia, aplastic anaemia and SLE syndrome.

Question 17

Clinical activity score for Graves’ orbitopathy

Answer 17

1. Spontaneous retrobulbar pain
2. Pain on eye movements
3. Eyelid erythema
4. Conjunctival injection
5. Chemosis
6. Swelling of the caruncle
7. Eyelid oedema or fullness

Question 18

Therapy for Graves’ orbitopathy

Answer 18

1. Symptomatic eg bed elevation, lubricants
2. Immunosuppressive - steroids, azathioprine
3. Radiotherapy
4. Orbital surgery ie decompression
5. Surgery for dysmotility
6. Occuloplastic surgery

Question 19

Features of hypothyroidism

Answer 19

1. Cold hands
2. Bradycardia
3. Muscle weakness in arms and legs
4. Hair coarse and thin
5. Face- pale and puffy
6. Brain - mental slowing, apathy and tiredness
7. Hoarse voice
8. Goitre
9. Constipation
10. Heavy periods
11. Skin - weight gain, intolerance to cold, reduced sweating, (cold, dry skin)

Question 20

Cause of hypothyroidism

Answer 20

1. Hashimotos -Goitre and high TPO Ab
2. Post ablative - RAI, Surgery, Drugs - Hx of therapy
3. Thyroiditis - Subacute (De Quervian’s), Postpartum - Biphasic illness
4. Drugs - Iodine, Lithium, Amiodarone, ATD
5. Secondary hypothyroidism - pit/ hypothalamic disease
6. Iodine deficiency - Endemic goitre
   Rare - Infiltration

Question 21

Pendred’s syndrome

Answer 21

Autosomal recessive
Goitre and sensorineural deafness
Impaired I organification
Cochlear malformation
Incidence 10/100,000
10% of cases of hereditary deafness