Hypothyroidism Flashcards
What is the difference in primary and secondary hypothyroidism? what is the commonest cause of hypothyroidism?
Primary - failing thyroid:
-low T3 and T4
-high TSH
(in primary subclinical hypothyroidism - TSH high but T3 and T4 normal)
Secondary - pituitary gland fail:
- low T3 and T4
- low TSH
How are the causes of primary hypothyroidism classified into 3 different classifications?
Goitrous: Hashimotos thyroiditis mainly, iodine deficiency
(also hereditary biosynthetic defects, maternally transmitted, drug induced)
Non-goitrous: atrophic thyroditis, congenital developmental defect, post surgery, post-radio iodine ablation, post radiation e.g. lymphoma
Self-limiting: following withdrawal suppressive thyroid therapy, subacute thyroiditis and chronic thyroiditis with transient hypothyroiditis, post-partum thyroiditis
What are the causes for secondary hypothyroidism?
Hypothalamic: congenital, infection (encephalitis), inflitration (sarcoidosis), malignancy (craniopharyngoma)
Pituitary: panhypopituitarism
What is hashimotos thyroiditis? what is it characterised by? what antibodies are seen?
- most common cause of hypothyroidism
- autoimmune destruction of thyroid gland
Characterised by:
- presence of thyroid peroxidase antibodies in blood
- T cell infiltration and inflammation on microscopy
Other antibodies?
- anti thyroglobulin antibodies (60%)
- TSH Rabs - blocking them (10-20%)
What is the epidemiology of hashimotos thyroiditis?
- middle aged women (45-60yrs)
- other AI disease
S/S hypothyroidism:
- skin/hair
- thermogenesis
- fluid retention
- cardiac
- metabolic
- GI
- resp.
- CNS
- Gynae
-skin/hair: coarse/dry/periorbital puffiness/pale/cool/doughy skin
- thermogenesis: intolerance to cold
- fluid retention: pitting oedema
- cardiac: bradycardia/cardiac dilatation/ pericardial effusion/worsening of heart failure
- metabolic: hyperlipideamia, decreased appetitis, wt gain
- GI: constipation
- resp.: deep/hoarse voice, macroglossia, obstructive sleep apnoea
- CNS: tired/decreased motor activities/peripheral neuropathy/prolongation of tendon jerks/carpal tunnel syndrome/ decreased visual acuity
- Gynae: menorrhagia, later oligo- or amenorrhea, hyperprolactinaemia
What other lab investigations are important for hypothyroidism?
- macrocytosis is typical
- elevated creatinine kinase
- hyperlipidaemia
- hyponatraemia (reduced renal tubular water loss)
- hyperprolactinaemia
How is hypothyroidism managed?
-normal metabolic rate has to be restored gradually
Younger patient:
-thyroxine at 50-100nanograms daily
Elderly/hx of IHD:
-25-50nanograms daily
adjust every 4 weeks according to response
- check TSH 2 mths after dose change
- once established check TSH every 12-18mths
- dose requirements may increase 25-50% in pregnancy
What is a myxoedema coma? who does this typically effect? what is found on ECG and ABG?
Severe hypothyroidism - usually effects women with longstanding but frequently unrecognised or untreated hypothyroidism (up to 60% mortality)
ECG:
- bradycardia
- low voltage complexes
- varying degress of heart block
- T wave inversion
- Prolongation of QT interval
ABG: type 2 resp. failure
- hypoxia
- hypercarbia
- resp. acidosis
(co-existing adrenal failure in 10% patients)`
What is the treatment for myxoedema coma?
ICU
- passively and slowly rewarm
- cardiac monitoring
- monitor BP, CVP, oxygenation, urine output, blood glucose levels
- fluids/fluid restrict/electrolyte balance
- broad spec. abiotics
- thyroxine cautious
What is amiodarone induced thyroid dysfunction?
- what proportion of patients are affected?
- how does this affect thyroid?
50% pts.
- thyrotoxicosis more frequently if low iodine intake
- hypothyroid more frequently if high iodine intake