Hypothyroidism Flashcards
what is it?
the signs and symptoms due to low levels of T3 and T4
results from any disorder which results in insufficient secretion of thyroid hormones from the thyroid gland
what is the difference between primary and secondary hypothyroidism
primary - gland failure, mag be a goitre - low free T3/T4 and high TSH
secondary to TRH or TSH - nor goitre secondary - low free T3/4 and low or normal TSH
What is myxoedema?
refers to severe hypothyroidism and is a medical emergency
what causes it?
majority of cases are due to Hashimoto’s thyroiditis an autoimmune disorder with a variety of antigenic targets
- affects middle aged women
- associated with other AI disease
- associated with HLA - DR3 and DR5
can also occur because of iodine deficiency, drugs (lithium etc.), post-therapy (surgery, 131I, irradiation), congenital abnormalities and in born errors of metabolism
rarely a result of secondary (pituitary or tertiary (hypothalamic) pathology
how does it present?
Reduced BMR Slow pulse rate Fatigue, lethargy, slow response times and mental sluggishness Cold-intolerance Tendency to put on weight easily In adults – Myxoedema – puffy face, hands & feet Babies - Cretinism – dwarfism & limited mental functioning due to deficiency of thyroid hormones present at birth Hair and skin o Coarse, sparse hair o Dull, expressionless face o Periorbital puffiness o Pale cool skin that feels doughy to touch o Vitiligo may be present o Hypercarotenaemia Thermogenesis – Cold intolerance Fluid Retention – Pitting oedema Cardiac o Reduced heart rate o Cardiac dilatation o Pericardial effusion o Worsening of heart failure Metabolic – Hyperlipidaemia Metabolic rate o Decreased appetite o Weight gain GI o Constipation o (Megacolon and intestinal obstruction) o (Ascites) Respiratory o Deep hoarse voice o Macroglossia o Obstructive sleep apnoea Neurology/CNS o Decreased intellectual and motor activities o Depression, psychosis, neuro-psychiatric o Muscle stiffness, cramps o Peripheral neuropathy o Prolongation of the tendon jerks o Carpal tunnel syndrome o (Cerebellar ataxia, encephalopathy) o Decreased visual acuity Gynae/reproductive o Menorrhagia o Later oligo- or amenorrhoea o Hyperprolactinaemia - ↑TRH causes ↑ PRL secretion
how is it managed?
normal metabolic rate should be gradually restored if rapid restoration it can precipitate cardiac arrythmias
young patients - start levothyroxine at 50-100µg daily
Elderly if history IHD – start levothyroxine at 25-50µg daily, adjusted every 4 weeks according to response
- Main treatment is levothyroxine (T4)
- No benefit with combination of T4 + T3
- T4 preferably taken before breakfast
- T3 therapy is rarely used: 20μg T3 = 100μg T4
- T3 effects develop within a few hours and disappear within 24-48 hours of discontinuation
- Dose requirements may increase by 25-50% in pregnancy (↑TBG)
how often should TSH be checked once treatment has been started?
2 months after dose change
every 12-18 months once stabilised
secondary hypothyroidism
TSH unreliable (decreased TCH production) so titrate dose of levothyroxine of the fT4 level
what is a myxoedema coma
normally in elderly women with long-standing, frequently unrecognised or untreated hypothyroidism
there is a high mortality - 60% despite early diagnosis and treatment
what are the findings of myxoedema coma?
ECG: bradycardia, low voltage complexes, varying degrees of heart block, T wave inversion, prolongation of the QT interval
Type 2 resp failure: hypoxia, hypercarbia, resp acidosis
co-existing adrenal failure is present in 10% of patients
how should myxoedema be managed?
intensive care A,B,C!
passively rewarm: aim for slow rise in body temperature
cardiac monitoring for arrhythmias
close monitoring of urine output, fluid balance, central venous pressure, blood sugars, oxygenation
broad spectrum antibiotics
thyroxine cautiously (hydrocortisone)
what causes goitrous primary hypothyroidism?
chronic thyroiditis (Hashimoto's thyroiditis) iodine deficiency drug-induced (e.g. amiodarone, lithium) maternally transmitted (e.g. anti-thyroid drugs) hereditary biosynthetic defects
what causes non-goitrous primary hypothyroidism?
atrophic thyroiditis
post-ablative therapy (e.g. radioiodine, surgery)
post-radiotherapy (e.g. for lymphoma treatment)
congenital developmental defect
what causes self-limiting primary hypothyroidism
following withdrawal of anti-thyroid drugs
subacute thyroiditis with transient hypothyroidism
post-partum thyroiditis
what are the laboratory findings for primary hypothyroidism?
↑TSH and ↓fT4/3 – cardinal abnormalities
Other abnormalities
Macrocytosis (↑MCV)
↑Creatine kinase (CK)
↑LDL-cholesterol
Hyponatraemia – ↓renal tubular water loss
Hyperprolactinaemia – ↑TRH leads to ↑PRL (often mild)
