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Endocrinology > Thyroid > Flashcards

Thyroid Flashcards

1
Q

What is the functional unit of the Thyroid?

A

Multiple, variable sized follicles, formed by single layer of epithelial cells filled with colloid.

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2
Q

What are the functions of T3

A 
Increases basal metabolic rate
Increases 02 and energy consumption
Stimulates protein synthesis and degradation
Increases glycogen breakdown 
Stimulates glucose synthesis
Stimulates breakdown of cholesterol
Increase HR, SV and CO
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3
Q

Define primary hypothyroidism

A

Insufficient levels of T3 and T4 as a result of problems with the thyroid. (High TSH, Low T4, T3)

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4
Q

Define central Hypothyroidism

A

Inadequate stimulation of the thyroid due to either reduced TSH from pituitary gland or inadequate release or thyrotropin-releasing hormone from the brains hypothalamus

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5
Q

Causes of hypothyroidism

A

Iodine deficiency (most common in developing countries)
Thyroidectomy
Auto-immune (Hashimoto’s, most common in developed countries)
Lithium based mood stabiliser (Lithium Carbonate)
Stress
Radioactive iodine therapy for Grave’s

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6
Q

Signs and symptoms of hypothyroidism

A 
Fatigue
Bradycardia
Constipation 
Cold intolerance
Hypoventilarion
Dry skin and hair
Weight gain
Myxoedema 
Myalgia
Menorrhagia
Deep voice
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7
Q

What tests would you order if you suspect hypothyroidism?

A

Serum TSH (elevated)
Free Serum T4, T3 (low)
Antithyroid Peroxidase Ab (Raised in Hashimoto’s)

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8
Q

What is the first line treatment for hypothyroidism? (Also what is the complication)

A

Levothyroxine

If over replaced there is an increased risk of osteoporosis and AF

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9
Q

Define hyperthyroidism

A

Excessive production of T3, T4 by the thyroid gland. (Low TSH, high T3, T4 is primary. High TSH, high T3,T4 is secondary)

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10
Q

Causes of hyperthyroidism

A

Auto-Immune (Grave’s disease, most common)
Thyroiditis (when acute releases stored TH but doesn’t produce more)
Pituitary Tumour
Increases iodine absorption (diet)
Multinodular goitre

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11
Q

Signs and Symptoms of Hyperthyroidism

A 
Hypermetabolic state
Heat intolerance
Increased appetite 
Weight loss
Frequent stools
Tachycardia
Tremor
Heart failure 
Warm, Smooth skin
Exophthalmos 
AF, depression, fatigue (in elderly)
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12
Q

What tests would you order if you suspect hyperthyroidism?

A

TSH (suppressed)
Serum free T4 (high)
Serum free or total T3 (high)
Free T3/Free T4 ratio

Consider:
TSH receptor Ab (positive)
Thyroid ultrasound (highly vascular; diffuse; enlarged)

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13
Q

What is a thyroid storm?

A

Excessive release of THs in individuals with hyperthyroidism. It is a life threatening, hypermetabolic state.

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14
Q

What is the first line treatment for a thyroid storm?

A

Antithyroid hormone (Propylthiouracil/carbinazole/thiamaze)

Corticosteroid (hydrocortisone)

B-Blocker (propranolol)

Lugosi solution (contains iodine to avoid exacerbation of thyroxicosis due to escape from Wolff-Chaikoff effect)

IV fluids

Oxygen

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15
Q

What is the Wolff-chaikoff effect?

A

Auto-regulatory phenomenon in which organification of iodine is inhibited resulting in elevated iodine levels which act as a negative feedback for TH production.

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16
Q

What is goitre?

A

Swelling of thyroid gland

17
Q

What initial investigations would you order if toxic multinodular goitre is suspected?

A

TSH (suppressed)

Investigations to consider:
free T4 or total T4 with measure of binding (elevated)
free T3 or total T3 with measure of binding (elevated)
I-123 thyroid scan and uptake (multiple hot and cold areas)

18
Q

Signs and symptoms of Goitre

A
  • enlarged thyroid
  • hypo/hyperthyroid or eurthyroid
  • dysphagia (obstruction)
  • difficulty breathing (airway obstruction)
19
Q

Signs and symptoms of Thyroid cancer

A

-hard painless nodule
-enlarged lymph node
-dysphagia
-dyspnea with obstruction
More common in women in early adulthood

20
Q

What are the initial investigations you will order if you suspect thyroid cancer?

A

TSH (normal)
fine-needle biopsy (cytology suggests histological features)
ultrasound, neck (Microcalcifications, Solid and Larger than 2 cm)
Laryngoscopy (may show ipsilateral paralysed vocal cord)

21
Q

Name some of the causes of goitre

A

lack of dietary iodine
hyperthyroidism
hypothyroidism
inflammation of the thyroid gland

22
Q

What is the function of the parathyroid?

A

Produce PTH, which regulates calcium blood levels

23
Q

Explain how PTH regulates blood calcium levels

A

On bone:

  1. Inhibits Osteoblasts, stimulates Osteoclasts
  2. Bone is broken down releasing Ca to blood

On kidneys:

  1. Stimulates kidney tubules to reabsorb calcium
  2. Inhibits reabsorption of phosphate (PO4-) which normally reduces Ca levels in the blood
  3. Stimulates kidney tubules to convert calcidiol to calcitriol (active vitamin D, 1,25-dihydroxyvitamin D)

On intestines:
Calcitriol stimulates absorption of calcium from the intestines.

24
Q

Explain the negative feedback of high blood calcium levels.

A
  1. Inhibits PTH secretion
  2. Stimulates parafollicar cells in the thyroid to secrete calcitonin secretion
    - Calcitonin stimulates osteoblasts, inhibits osteoclasts
    - Calcium leaves blood to build bone
25
Q

Define primary hyperparathyroidism

A

Disorder of one or more parathyroid glands resulting in overproduction of PTH and as a result high level of calcium in the blood.

26
Q

Define secondary hyperparathyroidism

A

Parathyroid overproducing PTH as a result of low calcium levels in the blood.

27
Q

Define tertiary hyperparathyroidism

A

Secondary hyperparathyroidism which is persistent and results in unregulated parathyroid and eventual high levels of calcium.

28
Q

What are the common causes of primary hyperparathyroidism?

A

Parathyroid adenomas
Multiple endocrine neoplasia (MEN-1,2,4) mutation
Hyperplasia
Lithium therapy

29
Q

What tests would you order if you suspect primary hyperparathyroidism?

A 
Serum calcium (normal high to elevated)
Serum intact PTH with immunoradiometric  (elevated)
CT neck (may be positive for solitary adenoma or multi-gland involvement)
Consider for complications:
25-Hydroxyvitamin D (calcidiol) levels (may be low)
Serum ALP (may be raised)
DXA scan: 
-1 to +1 = normal;
 -1 to -2.5 = osteopenia; 
< -2.5 = osteoporosis
30
Q

What are the common causes of secondary hyperparathyroidism

A

Anything causing hypocalcaemia:

  1. CKD (loss of 1 alpha hydroxylase activity)
  2. Malabsorption of Ca and Vitamin D(Chrons, Coeliac, whipples disease, gastric byass, chronic pancreatitis)
  3. Sepsis
  4. Thiazides
  5. Rhabdomyolysis
  6. Bisphosphonate treatment
31
Q

What is the treatment for primary hyperparathyroidism?

A

If symptomatic/ surgical indication:
1. parathyroidectomy

If they decline surgery or are asymptomatic:

  1. Monitor serum calcium, creatinine and bone density yearly.
  2. Adjunct. cinacalcet; can also give bisphosphonate therapy if they have osteoporosis
32
Q

Signs and symptoms of hyperparathyroidism

A 
Bone pain
Fatigue
Anxiety
Depression
Myalgia
Paraesthesia
Constipation
Urinary frequency 
Hx of Osteoporosis or osteopenia

Endocrinology (5 decks)

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