Thyroid Flashcards
Thyroid physiology
Hypothalamus secretes thyrotropin-releasing hormone (TRH), a tripeptide, that stimulates production of thyroid-stimulating hormone (TSH), a glycoprotein, from the anterior pituitary.
TSH increases production and release of T4 and T3 from the thyroid, which exert -ve feedback on TSH production.
Most T3 and T4 in plasma is protein bound, thyroxine-binding globulin (TBG).
Increased TSH and Decreased T4
Hypothyroidism
Increased TSH, normal T4
Treated hypothyroidism or subclinical hypothyroidism
Increased TSH, Increased T4
TSH secreting tumour or thyroid hormone resistance
Decreased TSH, Increased T4 or T3
Hyperthyroidism
Decreased TSH, normal T4 / T3
Subclinical hyperthyroidism
Decreased TSH, Decreased T4
Central hypothyroidism
Decreased TSH, T4 and T3
Sick euthyroidism or pituitary disease
Multiple methods of TSH activation
- Normal TSH secreting adenoma
- Graves’ disease
- Non autoimmune hyperthyroidism (Genetic)
Thyroid auto-antigen (TSHR)
Chromosome 14, G-protein receptor, receptor for TSH. Used for testing for Graves’ disease.
Auto-antigen thyroid peroxidase (TPO)
Chromosome 2, Haem enzyme, Used clinically in Hashimoto’s disease
Iodine in thyroid
Clinical consequences of reduced iodine.
- Newborn = increased mortality, cretinism, psycho motor deficits.
- Neonates, Infants and adults = Goitre and hypothyroidism (also in infants can retard growth)
Side effects of iodine
Iodine induces Hyperthyroidism, hypothyroidism, thyroiditis, modulation thyroid cancer
Causes of hyperthyroidism
- Graves’ disease
- Toxic multinodular goitre
- Toxic adenoma
- Thyroiditis - subacute, postpartum
- Drug induced - lithium, amiodarone
- TSH producing pituitary adenoma
7 etc
Treatment of hyperthyroidism
- Drugs (Carbimazole, Propylthiouracil, propanolol, steriods, lithium)
- Radioiodine therapy
Carbimazole
Prodrug converted to active form methimazole, prevents TPO enzyme coupling and iodising thyrosine residues of thyroglobin - thus reducing production of T3 and T4
SE: Skin rashes, agranulocytosis, pancreatitis, cholestatic jaundice, hepatitis, lymphadenopathy, thrombocytopenia, aplastic anaemia and SLE syndrome.
Clinical activity score for Graves’ orbitopathy
- Spontaneous retrobulbar pain
- Pain on eye movements
- Eyelid erythema
- Conjunctival injection
- Chemosis
- Swelling of the caruncle
- Eyelid oedema or fullness
Therapy for Graves’ orbitopathy
- Symptomatic eg bed elevation, lubricants
- Immunosuppressive - steroids, azathioprine
- Radiotherapy
- Orbital surgery ie decompression
- Surgery for dysmotility
- Occuloplastic surgery
Features of hypothyroidism
- Cold hands
- Bradycardia
- Muscle weakness in arms and legs
- Hair coarse and thin
- Face- pale and puffy
- Brain - mental slowing, apathy and tiredness
- Hoarse voice
- Goitre
- Constipation
- Heavy periods
- Skin - weight gain, intolerance to cold, reduced sweating, (cold, dry skin)
Cause of hypothyroidism
- Hashimotos -Goitre and high TPO Ab
- Post ablative - RAI, Surgery, Drugs - Hx of therapy
- Thyroiditis - Subacute (De Quervian’s), Postpartum - Biphasic illness
- Drugs - Iodine, Lithium, Amiodarone, ATD
- Secondary hypothyroidism - pit/ hypothalamic disease
- Iodine deficiency - Endemic goitre
Rare - Infiltration
Pendred’s syndrome
Autosomal recessive Goitre and sensorineural deafness Impaired I organification Cochlear malformation Incidence 10/100,000 10% of cases of hereditary deafness
