Thyroid disorders Flashcards by SN K

Explain the process of Thyroid Hormone Synthesis

1) Organification of iodide: Iodide → Iodine → condensed onto tyrosine residues → mono or di-iodinated tyrosine
2) Coupling reaction: 2 DIT molecules → T4
3) Release of the T3 and T4 from the thyroid gland
4) Major production of T3 occurs outside of the thyroid gland by peripheral conversion from T4

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Explain the hypothalamo-pituitary-thyroid axis

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Are primary or secondary disorders of thyroid gland more common?

Primary

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Are thyroid diseases more common in women or men

Women

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What are autoimmune thyroid disorders commonly associated with?

Other autoimmune diseases e.g. T1 DM, autoimmune adrenal insufficiency

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Is T3 or T4 more more biologically active

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What is Hyperthyroidism?

Over-production of thyroid hormone by the thyroid gland

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What is Thyrotoxicosis?

Abnormal and excessive quantity of thyroid hormone in the body

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Most common cause of Hyperthyroidism?

List 4 other common causes of thyrotoxicosis

Graves’ Disease ☆

Iatrogenic,
Toxic adenoma,
Toxic multinodular goitre
Thyroiditis
Iodide excess

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What is Graves disease? Incl the pathophysiology

Autoimmune condition where TSH receptor antibodies cause a primary hyperthyroidism.

These TSH receptor antibodies (TSHRAb) mimic TSH and stimulate TSH receptors on the thyroid

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What is subclinical hyperthyroidism?

Low levels of TSH but normal levels of T3 and T4

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List 4 symptoms of hyperthyroidism

Anxiety and irritability
Weakness and fatigue
Palpitations
Sweating and heat intolerance
Dyspnoea
Frequent loose stools (hyperdefecation)
Insomnia
Poor concentration
Menstrual abnormalities and sexual dysfunction

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List 4 signs of hyperthyroidism

Weight loss
Proximal myopathy
Tachycardia, arrythmias
Warm, moist skin
Tremor
Eye conditions (stare, lid lag, lid retraction)
Emotional lability
Hyperactive deep tendon reflexes with shortened relaxation time

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What is a Thyroid storm?

Exaggerated typical signs and symptoms, fever, jaundice, changes in neurologic function

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Clinical features/presentation specific to Graves disease

Diffuse goitre (without nodules)
Graves eye disease
Bilateral exophthalmos
Pretibial myxoedema

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Pathophysiology behind Graves’ Ophthalmopathy?

Antibodies to TSH receptor also target retroorbital tissues

T-cell inflammatory infiltrate → fibroblast growth
Severe: exposure keratopathy, diplopia, com-pressive optic neuropathy

Strong link with tobacco and seen in 50% of Graves Disease

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Pathophysiology behind Graves’ Myxedema (thyroid dermopathy)

Activation of fibroblasts → increased hyaluronic acid and chondroitin sulfate

Asymmetric, raised, firm, pink-to-purple, brown plaques of nonpitting edema

Occurs In <5% of Graves disease

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What is Thyroid acropachy?

List the 3 characteristic findings on imaging which comprise this

Rare complication of autoimmune thyroid disease

Digital clubbing
Soft tissue swelling of hands and feet
Periosteal bone formation

Occurs in 0.1-1 % and almost always in patients with myxedema and ophthalmopathy

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Laboratory findings indicative of primary hyperthyroidism?

Suppressed TSH (<0.05 uU/ml)

Elevated Free T4 and/or Free T3

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Ddx in a patient with hyperthyroidism for the follow values of T3:T4

T3:T4 > 20
T3:T4 < 20

T3:T4 > 20:

Graves’ Disease
Toxic MN Goiter

T3:T4 < 20:

Non-thyroid illness
Thyroiditis
Exogenous thyroxine

List 3 other investigations for hyperthyroidism

Thyroid radioiodine uptake
TSH receptor antibodies: Grave’s
US thyroid: hypoechogenic in untreated diffuse toxic goitre

What would iodine uptake show on nuclear scintigraphy for the following:

Toxic multinodular
Graves
De Quervain’s thyroiditis

TMG: Patchy uptake
Graves: diffuse, homogenous, increased uptake
DQ thyroiditis: globally reduced uptake of iodine-131

List 4 complications of hyperthyroidism

Atrial Fibrillation
Osteoporosis
Heart failure
Thyroid Storm

List 4 treatments of thyrotoxicois?

Antithyroid medications: Carbimazole and Propylthiouracil
β- blockers for symptom control (Propranolol preferred)
Radioactive iodine
Surgery

List 2 dangers/ side effects of Antithyroid medications

Carbimazole and Propylthiouracil can cause Agranulocytosis, and or hepatotoxicity (PTU)

What is hypothyroidism?

Inadequate output of thyroid hormones by the thyroid gland

List 4 populations at risk of hypothyroidism

1. Women 2. History of Graves disease or postpartum thyroid dysfunction 3. Elderly 4. Other autoimmune disease 5. Family history of thyroid disease, pernicious anemia, type I DM

Is primary or secondary hypothyroidism more common? What is the difference between these

1^o→ Thyroid gland insufficiency (more common) 2^o→ Pituitary pathology

What defines subclinical hypothyroidism?

Normal free T4 concentration in the presence of an elevated TSH concentration

What is the treatment of choice for hypothyroidism?

Levothyroxine (needs to be titrated)

List 4 causes of Hypothyroidism

1. Hashimoto's thyroiditis 2. Thyroiditis 3. Congenital hypothyroidism 4. Drug induced 5. Post radiation 6. Thyroid surgery

List 4 clinical features of hypothyroidism

1. Weight gain 2. Fatigue 3. Dry skin 4. Coarse hair and hair loss 5. Fluid retention (oedema, pleural effusions, ascites) 6. Heavy or irregular periods 7. Constipation

What is a Myxedema coma? How does it present?

Medical emergency - end stage of untreated/insufficiently treated hypothyroidism Presents with: 1. hypothermic 2. hypotensive 3. hypoventilation 4. bradycardic 5. Impaired sensorium

What is cretinism and why does it occur? List 3 clinical features

Lack of thyroxine from birth or before birth (severe and irreparable) From lack of thyroid gland or lack of iodine in mother 1. Mental defects 2. Stunted growth 3. Reduced growth and function of many organs

Typical clinical picture of a Myxedema Coma?

1. Elderly obese female 2. Becoming increasingly withdrawn, lethargic, sleepy and confused 3. Slips into a coma

List 4 physical findings of Myxedema Coma

1. Comatose or semi comatose 2. Hypothyroid features: dry coarse skin, hoarse voice, thin dry hair 3. Delayed reflex relaxation time 4. Hypothermia 5. Pericardial, pleural effusions, ascites

Typical history of a Myxedema Coma?

1. Previous thyroid surgery 2. Radioiodine 3. Default thyroid hormone therapy

List 4 things which may precipitate a Myxedematous Coma

1. Infections 2. Trauma (incl surgery) 3. Exposure to cold 4. CVS problems 5. Drugs

Management of Myxedema?

1. ICU admission - ventilatory support and IV meds 2. Parenteral thyroxine 3. Electrolytes - water restriction for hyponatremia, avoid fluid overload 4. Avoid sedation 5. Glucocorticoids - Hydrocortisone

List 4 factors which may reduce levothyroxine effectiveness

1. Malabsorption Syndromes ie. celiac disease 2. Drugs that ↑ clearance ie. rifampin 3. Factors that ↓ T4 to T3 clearance ie. amiodarone 4. ↓absorption ie. ferrous sulfate 5. Other Mechanisms ie. sertraline

What is Hashimoto’s Thyroiditis?

Autoimmune inflammation of the thyroid gland. Initially it causes a goitre after which there is atrophy of the thyroid gland.

List 2 antibodies which are associated with Hashimoto’s Thyroiditis

1. antithyroid peroxidase (anti-TPO) antibodies 2. antithyroglobulin antibodies

a) What is the most common cause of hypothyroidism in the **developed** word b) What is the most common cause of hypothyroidism in the **developing** world

a) Hashimoto’s Thyroiditis b) Iodine Deficiency

All treatments for **hyper**thyroidism have potential to cause hypothyroidism, list 4 of these

1. Carbimazole 2. Propylthiouracil 3. Radioactive iodine 4. Thyroid surgery

List 2 other medications which can cause hyperthyroidism

1. **Lithium** - inhibits production of thyroid hormones in the gland, can cause a goitre and hypothyroidism 2. **Amiodarone** - interferes with thyroid hormone production and metabolism, can cause both hypothyroidism and thyrotoxicosis

What findings on a thyroid function test would be indicative of a primary vs secondary cause of hypothyroidism?

1^o → low T3 & T4, high TSH 2^o → low TSH, low T3 & T4

What is secondary hypothyroidism?

Where the pituitary gland is failing to produce enough TSH. ## Footnote Often associated with a lack of other pituitary hormones ie. ACTH - known as 'hypopituitarism'

List 4 causes of secondary hypothyroidism

1. Tumours 2. Infection 3. Vascular (e.g. Sheehan Syndrome) 4. Radiation

What is Sheehan Syndrome?

Hypopituitarism caused by ischemic necrosis due to blood loss and hypovolemic shock during and after childbirth Also known as postpartum pituitary gland necrosis