Hypothyroidism

Question 1

List the signs of hypothyroidism?

Answer 1

• Decreased heat production -> cold intolerance
• Weight gain
• Decreased appetite
• Hypoactivity, lethargy
• Constipation
• Hyporeflexia
• Myopathy (proximal, increased CK)
• Myxedema (face, periorbital)
• Xanthalesmata
• Dry/cool skin
• Brittle hair
• Bradycardia
• Exertional dyspnoea
• Pericardial and pleural effusion

Question 2

List the signs of hyperthyroidism?

Answer 2

• Increased heat production -> heat intolerance
• Weight loss
• Increased appetite
• Hyperactivity, anxiety, tremor
• Diarrhoea
• Hyper-reflexia
• Myopathy (proximal, normal CK)
• Pretibial myxedema (Graves), periorbital oedema
• Exopthalmus (Graves), proptosis, lid retraction
• Warm, moist skin
• Fine hair
• Tachycardia, arrhythmia, systolic murmur
• Gynaecomastia
• Goitre (60-90%), thyroid bruit

Question 3

What are the causes of hypothyroidism?

Answer 3

1) Primary
o AI- Hashimoto’s disease (hyper then hypo)
o Drugs- radiaiton, amiodarone, lithium, antithyroid drugs (propolthyrouricil, methimazole)
o Congenital- absent/ectopic thyroid
o Infiltrative- haemochromatosis, sarcoidosis, amyloidosis,
o Dietary- iodine deficiency
o Infective- thyroiditis
o Wolff-Chaikoff effect (thyroid gland downregulation due to increaded iodine)

2) Secondary (lack of pituitary TSH)- pituitary disease
3) Tertiary (reduced hypothalamus thyrotropin releasing hormone -> usually stimulates pituitary TSH)- trauma, tumour, infiltrative disorder,

Question 4

What are the causes of hyperthyroidism?

Answer 4

• Graves’ disease
• Toxic multimodular goitre
• Thyroid storm

Question 5

Describe the TFT findings for hypo and hyperthyroidism?

Answer 5

Hypothyroidism:

• increased TSH
• decreased free T3 and T4
• hypercholesterolaemia (decreased LDL receptor expression)

Hyperthyroidism:

• decreased TSH
• increased free T3 and T4
• hypocholesterolaemia (increased LDL receptor expression)

Question 6

What investigations would you do for hypothyroidism?

Answer 6

Diagnostic:
- TFT
- thyroid US and biopsy
Bedside:
- ECG (bradycardia, pericardial effusion)
- CXR (pericardial and pleural effusion)
Labs:
- FBC
- CRP/ESR
- LFT
- EUC
- Lipid levels (hypercholesterolaemia)
- AI markers: 
o Graves disease (thyroid stimulating Ig)
o Hashimoto's disease (anti-thyroglobulin and anti-thyroid peroxidase) 
- Vit B12
LTM:
- nerve conduction studies (peripheral neuropathy)

Question 7

Describe the pathology of Hashimoto’s disease:

Answer 7

Pathology:
-> genetic predisposition (MHC class II loci HLA-DR3)
-> environmental trigger (viral thyroiditis)
-> defective regulatory T-cell function -> CD4 cells target thyroidal antigens
-> and B-cell clones produce auto-antibodies
-> autoantibodies to thyroglobulin and thyroid peroxidase
-> thyroid gland destroyed -> hypothyroidism
o Histo: Hurthle cells, lymphoid aggregates w germinal centres

Question 8

Describe the pathology of Graves’ disease?

Answer 8

Pathology: autoantibodies to TSH receptors -> thyroid-stimulating Ig (type 2 hypersensitivity)
-> stimulates TSH receptors (hyperthyroidism) and dermal fibroblasts (pretibial myxedema)
o Histo: tall, crowded follicular epithelial cells, scalloped colloid

Question 9

Describe the histopathological features of Hashimoto’s thyroiditis?

Answer 9

• Diffuse lymphoid infiltrates -> formation of lymphoid follicles
• Plasma cells
• Fibrosis
• Small nests of thyroid follicles w atrophic cells
• Chronic inflammation signs: hypervascularity, neoangiogenesis, venous stasis

Question 10

Explain the anatomy of the thyroid?

Answer 10

• Thyroid gland consists of 2 symmetrical lobes (each w narrow upper pole and broader lower pole), with a connecting isthmus of glandular tissue
• Location: anterior to the 2nd-4th tracheal rings

Question 11

Describe the arterial supply of the thyroid?

Answer 11

Arterial supply (2):
o Superior thyroid artery: external carotid -> superior thyroid a -> anterior branch (isthmus) and posterior branch (posterior aspect of lobe)
o Inferior thyroid artery: subclavian a -> thyrocervical trunk -> lower pole

Question 12

Describe the venous drainage of the thyroid?

Answer 12

Venous drainage (3):
o Superior thyroid vein -> internal jugular or facial v
o Middle thyroid vein -> internal jugular v
o Inferior thyroid vein -> brachiocephalic

Question 13

Describe the innervation of the thyroid?

Answer 13

Sympathetic supply: middle cervical ganglion

Question 14

What is sick euthyroid syndrome?

Answer 14

Sick euthyroid syndrome: abnormal thyroid function without underlying pathology
• Path: reduced T4 conversion as body tries to conserve calories during states of deficit or demand
- commonly post illness, with nutritional deficiency, glucocorticoids

Question 15

How would you treat hypothyroidism?

Answer 15

Thyroxine (T4)
• MA: acts as hormone replacement -> T4 converted to active T3 (higher efficacy, shorter half life) -> allows symptomatic stability
- Note: T3 levels self-regulated on background of T4
• CI: adrenal insufficiency (adrenal glands aid conversion of T4 to T3, large T4 build up can be toxic)

Question 16

What other autoimmune conditions are associated with Hashimoto’s thyroiditis?

Answer 16

• pernicious anaemia (anaemia due to Vit B12 deficit)
• Grave’s disease
• Addison disease (low ACTH by pituitary -> low adrenal cortisol)
• SLE
• RA
• Sjogren syndrome
• non-insulin dependent DM
• myasthenia gravis

Question 17

What are the possible causes of peripheral neuropathy in hypothyroidism?

Answer 17

o Hypothyroidism -> impaired neuronal transmission -> peripheral neuropathy, hyporeflexia, proximal hypothyroidm myopathy
o Vit B12 deficit (pernicious anaemia)- inadequate replacement Rx for prev episodes
o Nutritional deficiency (thiamine, pyridoxine, folate)

Question 18

List some complications of untreated hypothyroidism?

Answer 18

o CVS- hypercholesterolaemia (atherosclerosis), hypotension, bradycardia, heart block, CCF, pericardial effusion
o CNS- slowed mentation, deafness, cerebellar ataxia, pseudo-dementia, psychosis, stupor, coma
o GIT- faecal impaction/constipation, adynamic intestinal obstruction malabsorption (bacterial overgrowth in small bowel)

Question 19

What is a myxedema coma?

Answer 19

Myxedema coma
• Clinical: lethargy, coma, weakness, hypothermia, hypoventilation, hypoglycaemia, hyponatraemia
• Path: long-standing hypothyroidism -> reduced metabolic state and decreased O2 consumption
- hypothermia
- decreased drug metabolism -> medication overdose (esp sedatives)