Hypothyroidism Flashcards
List the signs of hypothyroidism?
- 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
List the signs of hyperthyroidism?
- 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
What are the causes of hypothyroidism?
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,
What are the causes of hyperthyroidism?
- Graves’ disease
- Toxic multimodular goitre
- Thyroid storm
Describe the TFT findings for hypo and hyperthyroidism?
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)
What investigations would you do for hypothyroidism?
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)
Describe the pathology of Hashimoto’s disease:
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
Describe the pathology of Graves’ disease?
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
Describe the histopathological features of Hashimoto’s thyroiditis?
- 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
Explain the anatomy of the thyroid?
- 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
Describe the arterial supply of the thyroid?
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
Describe the venous drainage of the thyroid?
Venous drainage (3): o Superior thyroid vein -> internal jugular or facial v o Middle thyroid vein -> internal jugular v o Inferior thyroid vein -> brachiocephalic
Describe the innervation of the thyroid?
Sympathetic supply: middle cervical ganglion
What is sick euthyroid syndrome?
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
How would you treat hypothyroidism?
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)
