Hypothyroidism/Thyroiditis Flashcards
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describe the hypothalamic pituitary thyroid axix (HPT axis)
hypothalamus produces TRH which stimulates anterior pituitary to produce ……..
how are thyroid hormones affected in primary hypothyroidism?
Free T3 and T4 = low
TSH = high (to try and compensate for the lack of T3 and T4 production)
how are thyroid hormones affected in primary hyperthyroidism?
free T3 and T4 = high
TSH = low (to try and reduce production of T3 and T4)
how are thyroid hormones affected in secondary hypothyroidism?
free T3 and T4 = low
TSH = low or normal (usually some condition affecting the anterior pituitary so less signalling to thyroid to produce T3 and T4)
how are thyroid hormones affected in secondary hyperthyroidism?
free T3 and T4 = high
TSH = high or normal (problem in anterior pituitary e.g TSH secreting tumour, loss of negative feedback response etc)
what is myxoedema?
severe hypothyroidism (medical emergency)
what is pretibial myxoedema?
rare clinical sign of graves disease
- autoimmune thyroid disease resulting in hyperthyroidism
in what populations is hypothyroidism more common?
white populations
women
older
areas of high iodine intake
what are the 3 causes of primary hypothyroidism?
goitorous
non-goitorous
self-limiting
examples of goitrous hypothyroidism?
chronic thyroiditis (hashimotos) iodine deficiency drug induced maternally transmitted hereditary defects
causes of non-goitrous hypothyroidism?
atrophic thyroiditis
post ablative therapy (surgery, radioiodine)
radiotherapy
congenital defect
causes of self limitng hypothyroidism?
withdrawal of antithyroid drugs
post partum
what can cause secondary hypothyroidism?
infiltrative infection malignancy trauma congenital cranial radiotherapy drug induced
what is hashimotos thyroiditis?
autoimmune hypothyroidism
- most common cause of hypothyroidism
autoimmune destruction of thyroid gland and reduced thyroid hormone production
what are the characteristics of hashimotos?
family history of autoimmune disease
antibodies against thyroid peroxidase (TPO)
t cell infiltrate and inflammation microscopically
what are the 3 stages in progression of thyroid disease?
euthyroid (normal)
mild thyroid failure
overt hypothyroidism
what are the clinical features of hypothyroidism?
coarse, sparse hair dull, expressionless face puffy face pale, cool skin (doughy to touch) vitiligo hypercarotenaemia cold intolerance fluid retention (pitting oedema) hyperlipidaemia decreased apetitie weight gain constipation megacolon and intestinal obstruction ascites deep hoarse voice macroglossia sleep apnoea
what are the cardiac features of hypothyroidism?
slow HR cardiac dilatation pericardial effusion worsening of heart failure hyperlipidaemia
neurological features of hypothyroidism?
decreased intellectual and motor activities depression, psychosis muscle stiffness, cramos peripheral neuropathy prolonged tendon jerks carpal tunnel decreased visual acuity
reproductive features of hypothyroidism?
menorrhagia
later oligo or amenorrhoea
hyperprolactinaemia
lab investigations for primary hypothyroidism?
increased TSH and low T3/4 increased MCV raised LDL raised CK low sodium hyperprolactinaemia
graves disease autoantibodies?
anti TPO (70-80%) anti thyroglobulin (30-50%) TSH receptor antibody (70-100%)
autoantibodies in autoimmune hypothyroidism?
anti TPO (95%)
anti-thyroglobulin (60%)
TSH receptor antibody (10-20%)
how is hypothyroidism managed?
restore metabolic rate slowly to prevent arrhythmia
younger = levothyroxine 50-100 micrograms daily
elderly = 25-50 micrograms daily
check TSH 2 months after dose change then every 12-18 months once stabilised
what is levothyroxine and how is it used?
T4
taken before breakfast
no benefit of combining with T3
may need to increase dose by 20-25% in pregnancy (due to increased TBG)
who does myxoedema coma usually affect?
elderly women with long standing untreated hypothyroidism
what are the features of myxoedema coma?
bradycardia
type 2 resp failure
co-existing adrenal failure (in 10%)
reduced consciousness
how is myxoedema coma managed?
ICU slowly warm up patient monitor heart, urine, fluids, BP, BG and sats antibiotics thyroxine cautiously (hydrocortisone)
thyrotoxicosis vs hyperthyroidism?
thyrotoxicosis = any state arising from tissues being exposed to excess thyroid hormone (can be from medication) hyperthyroidism = specific to overactivity of thyroid hormone leading to thyrotoxicosis
signs of hyperthyroidism/thyrotoxicosis?
palpitations AF cardiac failure (rare) tremor sweating anxiety, nervous, irritable, sleep disturbance
symptoms of thyrotoxicosis?
loose bowels lid retraction double vision proptosis brittle, thin hair rapid fingernail growth light/less frequent periods muscle weakness weight loss despite increased appetite intolerance to heat
causes of hyperthyroidism?
excessive thyroid stimulation - graves - thyrotropinoma - thyroid cancer - choriocarcinoma thyroid nodules with autonomous function - toxic solitary nodule - toxic multinodular goitre
causes of thyrotoxicosis (not associated with hyperthyroidism)?
thyroid inflammation - subacute (de quervains) thyroiditis - post partum thyroiditis - drug induced (amiodarone) exogenous thyroid hormones - over treatment with levothyroxine - thyrotoxicosis factitial ectopic thyroid tissue - metastatic thyroid carcinoma - struma ovarii
risk factors for graves disease?
younger - 20-50 yrs
sisters and children of women with graves disease
smoking
interacting susceptibility genes and environmental factors
lab investigations in graves disease?
reduced TSH and increased T3/4 hypercalcaemia raised alk phosphate leucopenia (low WCC) TSH receptor antibody (TRAb) - diagnostic if present so imaging not needed
what clinical signs are specific to graves disease?
pretibial myxoedema
thyroid acropachy (clubbing with thyrotoxicosis)
thyroid bruits (assoc with very large goitres)
graves eye disease
what is graves eye disease?
TRAb driven pathology of the eye seen in graves - can affect one or both eyes
also called thyroid eye disease (TED) and graves opthalmopathy (GO)
can be sight threatening
often causes protrusion of eyes
how is graves eye disease managed?
use clinical activity score (CAS, Mouritis)
mild = topical lubricants
severe = steroids, radiotherapy, surgery
what are the features of nodular thyroid disease?
asymmetrical goitre
thyroid may feel nodular
insidious onset
usually older patients
lab tests in nodular thyroid disease?
increased T3/4
low TSH
antibody negative (unless co-exsisting graves disease - would show TRAb)
Scintigraphy shows high uptake
what is a thyroid storm/crisis?
medical emergency severe hyperthyroidism hyperthermia resp and cardiac collapse exaggerated reflexes typically seen in hyperthyroid patients with an acute infection/illness or recent surgery
mainstay of treatment in hyperthyroidism?
anti-thyroid drugs (ATDs)
- carbimazole = first line
- propylthiouracil = first line in 1st trimester of pregnancy as less potent
specific hyperthyroidism treatment if graves disease/
dose titration for 12-18 months then stop medication
or
block and replace for 6 months
relapse is common
what are some common side effects of ATDs?
allergy
liver disturbance
agranulocytosis (rare, happens in first 6 weeks)
signs of agranulocytosis in ATD treatment?
fever
mouth ulcers
oropharyngeal infection
what other drugs are used in hyperthyroidism?
Beta blockers (propanalol, or CCB if asthmatic) radioiodine (first line for relapsed graves, don't use in pregnancy)
risk of radioiodine?
hypothyroidism when used in graves
when might a thyroidectomy be indicated?
if radioiodine is contraindicated
risks = recurrent laryngeal nerve palsy, hypothyroidism
what can cause thyroiditis?
hashimotos post partum drug induced (amiodarone, lithium) radiation acute suppurative thyroiditis (bacterial)
what are the features of subacute thyroiditis?
20-50 triggered by viral infection neck tenderness fever other viral symptoms self limiting over a few months
how does amiodarone affect the thyroid?
inhibits DIO1 - decreased T3 and T4, normal TSH
causes abnormal TFTs in 50% of people
causes hypothyroidism slightly more commonly than hyperthyroidism
what is subclinical thyroid disease?
abnormal TSH with normal thyroid hormone
risk factors for subclinical hypothyroidism, when is it managed?
if strongly TPO positive
treat if TSH >10 or pregnant
what are the risks for subclinical hyperthyroidism and when is it treated?
multinodular goitre
osteoporosis
AF
treatment if TSH <0.1 or co-existing osteoporosis/AF
what is non-thyroidal illness?
“sick euthyroid syndrome”
impact of incurrent illness on HPT axis causing suppression of TSH and then rise during recovery
