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Hyper/hypothyroidism Flashcards

(52 cards)

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1
Q

What are the 4 major histological components of the thyroid gland?

A

Follicle - secretory sac containing colloid
Colloid - mixture which contains prohormone thyroglobulin
Follicular cells - cells which make up the follicle
Parafollicular cells (C-cells) - calcitonin secreting cells

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2
Q

Describe the steps in the formation of thyroid hormone.

A
  1. Iodine taken up by follicular cells and passed into colloid.
  2. Iodine attaches to thryoglobulin forming either monoiodotyrosine (MIT) ot di-iodotyrosine (DIT)
  3. MIT+DIT = triiodothyronine (T3)
    DID+DID = thyroxine (T4)
  4. T3 and T4 stored in colloid
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3
Q

Describe the steps in the secretion of thyroid hormone.

A
  1. Thyroid releasing hormone (TRH) secreted from hypothalamus and acts on anterior pituitary gland to release thyroid stimulating hormone (TSH).
  2. TSH acts on G-protein coupled receptors on follicular cells which increases intracellular cAMP
  3. Stimulates transportation of T3/T4 into follicular cells by and then into the blood by pinocytosis
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4
Q

What is the active form of thyroid hormone?

A

T3 (triiodothyronine)

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5
Q

What transports thyroid hormone in the blood?

A

Thyroxine binding protein (70%)

Also transthyretin (20%) and albumin (5%)

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6
Q

Describe the steps in the action of thyroid hormone.

A
  1. T3/T4 enters cell through membrane transporter and T4 converted to T3 by de-iodinase 2 (D2) enzymes in cytoplasm
  2. T3 binds to and activates thyroid hormone receptor in the nucleus
  3. This converts inhibitoary co-repressor (CoR) to co-actuivator (CoA) protein which binds to thyroid response element (TRE) on DNA increasing metabolic rate
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7
Q

What enzyme converts T4 to T3 inside tissues?

A

Deiodinase 2 (D2)

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8
Q

What is hyperthyroidism?
What is thyrotoxicosis?

Why are they different?

A

Hyperthyroisism - overactive thyroid gland

Thyrotoxicosis - state arising when tissues exposed to excess thyroid hormone

Thyrotoxicosis can occur without hyperthyroidism e.g. excess exogenous thyroxine, ectopic thyroid tissue

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9
Q

What is primary hyperthyroidism?

A

Problem within the thyroid gland causing hypersecretion.

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10
Q

TFTs show:

  • T3/4: high
  • TSH: low

Diagnosis?

What test would you do next and why?

A

Primary hyperthyroidism

TSH receptor antibody (TRAb): helps differentiate Graves’ disease from mutinodular goitre/solitary toxic nodule

TRAb elevated - Graves

TRAb low - not Graves

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11
Q

What is Graves’ disease?

A

Autoimmune condition of the thyroid gland (thyroid receptor antibody - TRAb) causing hyperthyroidism

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12
Q

How does Graves’ disease present?

A 
Tachycardia, anxiety, sweating, tremor
Muscle weakness
Weight loss and increased appetite
Diarrhoea
Light periods/amenorrhoea

Proptosis

Smooth goitre

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13
Q

What is pretibial myxoedema?

A

Swelling and lumpiness of shins from Graves’ disease

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14
Q

What is Thyroid Eye Disease (TED)?

A

Exopthalmus, lid retraction and painful eye movements caused by Graves’ disease

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15
Q

Are thyroid cancers normally

  • hyperthyroid
  • euthyroid
  • hypothyroid?
A

Usually euthyroid

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16
Q

What is choriocarcinoma and why can it cause hyperthyroidism?

A

Tumour secreting human chorionic gonadotrophin (hCG)

Has a very similar structure to TSH (alpha chains identical, ß chain different) and can mimic its effects

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17
Q

What does amiodarone do to T3/4 levels and why?

What is the clinical significange of this?

A

Amiodarone inhibits deiodinase 1 (DIO1) which converts T4 to T3 resulting in high T4 and low T3

This tends to cause

  • hyperthyroidism in iodine deficient areas
  • hypothyroidism in iodine rich areas
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18
Q

TFTs show:

  • T3/4: high
  • TSH: high

Diagnosis?

A

Secondary hyperthyroidism

Dysfunctional hypothalamic-pituitary-thyroid axis producing excess TSH and consequent T3/4

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19
Q

TFTs show:

  • T3/4: normal
  • TSH: low

Diagnosis?

A

Subclinical hyperthyroidism

Biological state which has risk of progressing to overt hyperthyoidism

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20
Q

How is hyperthyroidism treated?

A

Anti-thyroid drugs (carbimazole, propylthiouriacil)

ß-blockers

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21
Q

Patient in first trimester of pregnancy is diagnosed with hyperthyroidism. What treatment do you prescribe?

Study These Flashcards
A

Propylthiouracil

22
Q

Name 2 anti-thyroid drugs and their different characteristics.

Study These Flashcards
A

Carbimazole

  • first line
  • once daily
  • less side effects
  • more potent

Propylthiouracil

  • second line (unless 1st trimester of pregnancy)
  • twice daily
  • more side effects
  • less potent
23
Q

What is the most important side effect to warn patients on anti-thyroid drugs (ATD) about?

Study These Flashcards
A

Agranulocytosis

(warn patient verbally and in writing that if they get fever they must stop drugs and get urgent FBC)

Patient can never use ATD again.

24
Q

How do you manage a patient with hyperthyroidism who developed agranulocytosis after using antithyroid medication?

Study These Flashcards
A

Radioiodine

Thyroidectomy if radioiodine contraindicated (pregnancy, active thyroid eye disease)

25
What is the main risk in thyroidectomy?
Recurrent laryngeal nerve palsy
26
What is a thyroid storm?
Acute and serious attack of hyperthyroidism usually affecting hyperthyroid patient who suffers acute infection/surgery
27
How do you manage thyroid storms?
ABC High dose antithyroid drugs Hydrocortisole Potassium iodide
28
TFTs show: - T3/4: low - TSH: high Diagnosis? What test would you do next and why?
Primary hypothyroidism Anti-thyroid peroxidase (anti-TPO) Would be raised in Hashimoto's thyroiditis
29
How does Hashimoto's thyroiditis present?
Weight gain, lethargy, puffy skin, bradycardia, consipation Menorrhagia/amenorrhoea Slow tendon jerks Goitre
30
Why does hypothyroidism cause oligo/amenorrhoea?
Increased TRH increases prolactin secretion. Prolactin inhibits gonadotrophin action
31
What treatments can cause hypothyroidism?
Radiotherapy Amiodarone Lithium Thyroidectomy
32
What is the commonest cause of hypothyroidism 1. in the UK 2. worldwide?
1. Hashimoto's thyroiditis | 2. Iodine deficiency
33
TFTs show: - T3/4: low - TSH: low Diagnosis?
Secondary hypothyroidism Dysfunctional hypothalamic-pituitary-thyroid axis
34
TFTs show: - T3/4: normal - TSH: high Diagnosis?
Subclinical hypothyroidism
35
What does hypothyroidism cause in babies? Why is this rare?
Cretinism: dwarfism and poor mental function (thyroid hormones important in brain development) Guthrie screening test (5th day of life TFTs done) means this is rare
36
How do you treat primary hypothyroidism?
Slowly increase thyroid levels with daily levothyroxine (T4 tablets)
37
What doses of levothyroxine are used in 1. normal patients? 2. elderly? 3. pregnant women?
1. 50-100µg 2. 25-50µg (half) 3. Increase previous dose by 25µ
38
What is myxoedema coma?
Potentially fatal loss of brain function from severe hypothyroidism
39
How does myxoedema coma present?
Hypothyorid signs Reduced mental status Hypothermia Respiratory failure
40
How do you manage myxoedema coma?
``` ABC Slowly rewarm Broad spectrum antibiotics Cautious thyroxine Hydrocortisone if adrenal failure ```
41
What is sick euthyroid syndrome?
Abnormal TFTs caused by non-thyroid illness Avoid checking TFT in ill patient without clinical indication of thyroid pathology
42
What TFT pattern often shows in ill people?
Sick euthyroid syndrome - T3/4: low - TSH: low
43
How would resistance to thyroid receptor hormone alpha (TRa1/2 mutation) present?
Delayed development Bradycardia Chronic consiptation
44
How would resistance to thyroid receptor hormone beta (TRß1/2 mutation) present?
Increased T3/4 and TSH Goitre Affected colour vision
45
Is resistance to thyroid receptor alpha or beta more common?
resistance to thyroid receptor hormone beta is more common
46
What does thyroiditis show on scintigraphy?
Homogenously reduced iodine uptake
47
What is the classic effect of thyroidtitis on thyroid hormone levels?
Increased initially Hypothyroid after Euthyroid once inflammation settles
48
Name 3 causes of thyroiditis and when they would present.
De Quervian's thyroiditis - after viral infection Post-partum thyroiditis - after pregnancy Drug induced thyroiditis - after treatment with amiodarone/lithium
49
What TFT pattern do multinodular goitres often show?
Subclinical hyperthyroidism (normal T3/4, low TSH) This can progress to primary hyperthyroidism (high T3/4, low TSH)
50
What investigations can be done if patient presents with breathlessness and a multinodular goitre?
CT scan Flow volume loops
51
What does a multinodular goitre often show on scintigraphy?
Multiple nodules but one dominant nodule taking up most of the iodine
52
When is surgery indicated in toxic multinodular goitre?
Tracheal compression Retrosternal extension Cancer suspicion

Endocrinology (10 decks)

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