define
underactive thyroid caused by low levels of T3 and T4
two types of hypothyroidism
overt
subclinical
causes of primary hypothyroidism
- goitrous e.g. Hashimoto’s thyroiditis, iodine deficiency, drug induced (amiodarone, lithium), maternally transmitted (ATDs) or hereditary biosynthetic defects
- non-goitrous e.g. atrophic thyroiditis, post-ablative therapy (RAI, surgery), post-radiotherapy (lymphoma treatment) or congenital development defect
- self-limiting e.g. withdrawal of ATDs, subacute thyroiditis with transient hypothyroidism and post-partum thyroiditis
presentation
- hair and skin= coarse, sparse, dull, expressionless, periorbital puffy, pale, cool skin, vitiligo and hypercarotenaemia
- thermogenesis= cold intolerance
- fluid retention= pitting oedema
- cardiac= reduced HR, cardiac dilation, pericardial effusion and HF
- metabolic= reduced BMR, hyperlipidaemia, decreased appetite and weight gain
- GI= constipation, megacolon and ascites
- respiratory= deep hoarse voice, macroglossia and sleep apnoea
- CNS= depression, muscle cramps, peripheral neuropathy, lethargy, slow response, prolonged of tendon jerks, carpal tunnel, decreased visual acuity
- gynae/ reproductive= menorrhagia, olgio/amenorrhoea
- myxoedema
- babies can have cretinism (dwarfism and limited mental function)
diagnosis of hypothyroidism
high TSH and low T3/4
high MCV, CK, LDL cholesterol and PRL
hyponatraemia (renal tubular water loss)
autoantibodies e.g. anti-TPO, anti-thyroglobulin and TSH receptor antibody
management of hypothyroidism
levothyroxine
dosing of levothyroxine
young= 50-100ug daily elderly= 25-50ug daily take before breakfast adjust every 4 weeks according to respond dose increased in pregnancy
why is it important to begin levothyroxine slowly?
risk of cardiac arrhythmias
how often should you check TSH when started on levothyroxine?
check TSH every 2 months after any dose change then once stabilised check every 12-18 months
how to dose levothyroxine in secondary hypothyroidism?
titrate to T4 as TSH unreliable
who does myxoedema coma usually affect?
typically elderly women with long standing but frequently unrecognised and untreated hypothyroidism
diagnosis of myxoedema coma
- ECG= bradycardia, low voltage complexes, heart block T wave inversion and prolongation of QT interval
- type 2 respiratory failure= hypoxia, hypercarbia, respiratory acidosis
- co-existing adrenal failure
management of myxoedema coma
- ABCDE, passively rewarm, aim for slow rise
- cardiac monitoring for arrhythmias and monitor urine output, fluid balance, central venous pressure, blood sugars and oxygenation
- broad spectrum antibiotics
- thyroxine cautiously and hydrocortisone if adrenal failure
define Hashimoto’s thyroiditis
gradual failure of thyroid function, due to AI destruction, associated with other AI disease and HLA-DR3/5
who does Hashimoto’s most commonly affect?
females 45-60
often FH
presentation of Hashimoto’s
hashitoxicosis (transient hyperfunction)
risk of developing B cell NHL in affected gland
diagnosis of Hashimoto’s
- antibodies e.g. anti-thyroglobulin and anti-thyroid peroxidae (TPO)
