Endo

Question 8

describe the HPT axis

Answer 8

• the hypothalamus secretes thyrotropin-releasing hormone (TRH) - this stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH).
• This then acts on the thyroid gland increasing the production of thyroxine (T4) and triiodothyronine (T3)

Question 9

hypothyroidism classifications

Answer 9

Hypothyroidism may be classified as follows:
- primary hypothyroidism: there is a problem with the thyroid gland itself, for example an autoimmune disorder affecting thyroid tissue (see below)
- secondary hypothyroidism: usually due to a disorder with the pituitary gland (e.g.pituitary apoplexy) or a lesion compressing the pituitary gland
- congenital hypothyroidism: due to a problem with thyroid dysgenesis or thyroid dyshormonogenesis

Question 10

causes of hypothyroidism

Answer 10

1. Hashimoto’s thyroiditis
* most common cause in the developed world
* autoimmune disease, associated with type 1 diabetes mellitus, Addison’s or pernicious anaemia
* may cause transient thyrotoxicosis in the acute phase
* 5-10 times more common in women

2. Subacute thyroiditis (de Quervain’s)
associated with a painful goitre and raised ESR

3. Riedel thyroiditis
* fibrous tissue replacing the normal thyroid parenchyma
* causes a painless goitre

4. Postpartum thyroiditis

5. Drugs: lithium + amiodarone

6. Iodine deficiency: the most common cause of hypothyroidism in the developing world

Question 11

causes of hyperthyroidism

Answer 11

1. Graves’ disease
   * most common cause of thyrotoxicosis
   * as well as typical features of thyrotoxicosis, other features may be seen including thyroid eye disease
2. Toxic multinodular goitre
   autonomously functioning thyroid nodules that secrete excess thyroid hormones
3. Drugs
   amiodarone

Question 12

sx of hypothyroidism vs thyrotoxicosis

Answer 12

Question 13

low TSH + high T4 =

Answer 13

Thyrotoxicosis (e.g. Graves’ disease)

Question 14

high TSH + low T4 =

Answer 14

Primary hypothyroidism (e.g. Hashimoto’s thyroiditis)

Question 15

low TSH + low T4 =

Answer 15

Secondary hypothyroidism
OR
Sick euthyroid syndrome - Common in hospital inpatients. Changes are reversible upon recovery from the systemic illness and no treatment is usually needed

Question 16

high TSH + normal T4 =

Answer 16

Subclinical hypothyroidism - pt en route to hypothyroidism. TSH is the more sensitive early marker.
OR
poor compliance with thyroxine meds if pt already diagnosed.

Question 17

graves diseases autoantibody

Answer 17

TSH receptor antibodies are present in around 95%

Question 18

Hashimoto’s disease autoantibody

Answer 18

Anti-TPO antibodies are present in around 90%

Question 19

other investigations to test for hyperthyroidism

Answer 19

• nuclear scintigraphy; toxic multinodular goitre reveals patchy uptake
• blood glucose: hyperthyroid is associated with hyperglycaemia
• ECG: hyperthyroid is associated with AF
• Thyroid ultrasound – for pts with thyrotoxicosis + a paplpable thyroid OR pts with normal thyroid fx when malignancy is suspected.

Question 20

Patients with thyrotoxicosis may be treated with:

Answer 20

• propranolol: this is often used at the time of diagnosis to control thyrotoxic symptoms such as tremor
• carbimazole: blocks thyroid peroxidase from coupling and iodinating the tyrosine residues on thyroglobulin → reducing thyroid hormone production. Agranulocytosis is an important adverse effect to be aware of
• radioiodine treatment

Question 21

Hypothyroidism: features

Answer 21

General
* Weight gain
* Lethargy
* Cold intolerance
* GOITRE - seen in hashimoto’s

Skin
* Dry (anhydrosis), cold, yellowish skin
* Non-pitting oedema (e.g. hands, face)
* Dry, coarse scalp hair, loss of lateral aspect of eyebrows

Gastrointestinal
* Constipation

Gynaecological
* Menorrhagia

Neurological
* Decreased deep tendon reflexes
* Carpal tunnel syndrome

A hoarse voice is also occasionally noted.

Question 22

levothyroxine starting therapy

Answer 22

• 50-100mcg for most patients
• 25mcg for:
  
  • elderly pts
  • cardiac disease pts
  • pts >50yrs
  • severely hypothyroid pts
• monitor after 2-3 months treatment

Question 23

how would a pregnant woman with established hypothyroidism be managed

Answer 23

• women with established hypothyroidism who become pregnant should have their dose increased by at least 25-50 micrograms levothyroxine due to the increased demands of pregnancy.
• The TSH should be monitored carefully, aiming for a low-normal value

Question 24

side effects of levothyroxine

Answer 24

• hyperthyroidism: due to over treatment
• reduced bone mineral density - over-replacemtn increases the risk of OP.
• worsening of angina
• atrial fibrillation

Question 25

Subacute (De Quervain's) thyroiditis: cause

Answer 25

viral infection

Question 26

Subacute (De Quervain's) thyroiditis: presentation

Answer 26

* usually presents as hypERthyroidism and occurs in phases 1. Hyperthyroidism, painful goitre, raised ESR. Lasts 3-6 weeks.[globally reduced uptake of radioactive iodine] 2. Euthyroid: lasts about 1-3 weeks 3. Hypothyroidism. Lasts weeks-months 4. Thyroid structure and function goes back to normal.

Question 27

Subacute (De Quervain's) thyroiditis: investigaton

Answer 27

thyroid scintigraphy: globally reduced uptake of iodine-131

Question 28

Subacute (De Quervain's) thyroiditis: Mx

Answer 28

* self-limiting * supportive mx: NSAIDs for pain relief * CSX used inmore severe cases.