Hypo/Hyperthyroidism Flashcards
What is a primary thyroid disease?
Disease affecting thyroid gland itself, can occur with goitre (goitrous) or without (non-goitrous), most commonly autoimmune
What is a secondary thyroid disease?
Hypothalamic or pituitary disease, no thyroid gland pathology
What is the other name for thyroid stimulating hormone (TSH)?
Thyrotropin = reflects tissue thyroid hormone action
What releases TSH?
Released by thyrotroph cells in anterior pituitary in response to thyrotropin releasing hormone (TRH)
What are the blood abnormalities for primary hypothyroidism and hyperthyroidism?
Hypo = free T3/4 low, TSH high Hyper = free T3/4 high, TSH low
What are the blood abnormalities for secondary hypothyroidism and hyperthyroidism?
Hypo = free T3/4 low, TSH low (or normal) Hyper = free T3/4 high, TSH high (or normal)
What is myxoedema?
Severe hypothyroidism = medical emergency
What is pretibial myxoedema?
Rare clinical sign of Grave’s disease, which causes hyperthyroidism
What are some features of hypothyroidism?
Increased TSH in 7.5% of females and 2.5% of males >65, incidence higher in white populations and areas of high iodine intake
What are some causes of primary goitrous hypothyroidism?
Chronic thyroiditis, iodine deficiency, drug induced, maternally transmitted, hereditary biosynthetic defects
What are some causes of primary non-goitrous hypothyroidism?
Atrophic thyroiditis, post-ablative therapy, post-radiotherapy, congenital developmental defect
What are some features of Hashimoto’s thyroiditis?
Most common causes of hypothyroidism in Western world, often family history, more common in females
What occurs in Hashimoto’s thyroiditis?
Autoimmune destruction of thyroid gland and reduced thyroid hormone production
What is Hashimoto’s thyroiditis characterised by?
Antibodies against thyroid peroxidase (TPO), and T cell infiltrate and inflammation microscopically
What are some general symptoms of hypothyroidism?
Coarse sparse hair, dull expressionless face, periorbital puffiness, doughy pale cool skin, vitiligo, hypercarotenaemia, cold intolerance, hyperlipidaemia
What are some cardiac and GI symptoms of hypothyroidism?
Cardiac = slow heart rate, cardiac dilation, pericardial effusion GI = weight gain, decreased appetite, constipation
What are some CNS symptoms of hypothyroidism?
Depression, psychosis, muscle stiffness, peripheral neuropathy, carpal tunnel syndrome
What are some reproductive symptoms of hypothyroidism?
Menorrhagia, oligo/amenorrhoea, hyperprolactinaemia
How are primary causes of hypothyroidism investigated?
Increased TSH and decreased T3/4 Increased MCV (microcytosis), increased CK, increased LDL, hyponatraemia, hyperprolactinaemia
What antibodies are linked to primary hypothyroidism?
Anti-TPO = 95%
Anti-Tg = 60%
TSH receptor = 10-20%
Why does normal metabolic rate need to be restored gradually in hypothyroidism?
Doing it too quickly may cause cardiac arrhythmias
How are young patients with hypothyroidism treated?
Start levothyroxine at 50-100 micrograms daily
How are elderly patients with hypothyroidism treated?
Levothyroxine at 25-50 micrograms daily = adjusted every 4 weeks according to response
How often should TSH be checked in patients with hypothyroidism?
Check 2 months after any dose change, once stabilised check every 12-18 months
TSH unreliable in secondary causes
How is T3 used to treat hypothyroidism?
Very rarely used = more potent than T4 therapy, effects develop within a few hours and disappear within 24-48hrs of stopping
How is typically affected by myxoedema comas?
Elderly women with long standing but frequently untreated hypothyroidism
Are myxoedema comas a medical emergency?
Yes = mortality up to 60%, type 2 respiratory failure occurs , treated with ABCDE approach, antibiotics and hydrocortisone
What are the ECG features of myxoedema comas?
Bradycardia, low voltage complexes, heart block, T wave inversion, prolonged QT
What does thyrotoxicosis describe?
The clinical state arising when tissues are exposed to excess thyroid hormone
What does hyperthyroidism refer to?
Refers specifically to conditions in which overactivity of the thyroid gland leads to thyrotoxicosis
What are the cardiac and CNS symptoms of thyrotoxicosis?
Cardiac = palpitations, AF, cardiac failure (rare), tremor CNS = anxiety, nervousness, irritability, sleep disturbance, muscle weakness, sweating
What are some general symptoms of thyrotoxicosis?
Diarrhoea, weight loss, lighter less frequent periods, eyelid retraction, double vision, proptosis (specific to Grave’s)
What are some causes of thyrotoxicosis that are associated with hyperthyroidism?
Excessive stimulation = Grave’s, Hashitoxicosis, thyrotropinoma (very rare), choriocarcinoma
Toxic solitary nodule, toxic multinodular goitre
What are some causes of thyrotoxicosis that aren’t associated with hyperthyroidism?
Subacute thyroiditis, postpartum thyroiditis, drug-induced thyroiditis, over treatment with levothyroxine, thyrotoxicosis factitial, metastatic thyroid carcinoma, struma ovarii
What are some features of Grave’s disease?
Common in young (20-50 years), more common in women, influenced by smoking, associated with osteoporosis
What do the investigations for Grave’s disease show?
Decreased TSH and increased T3/4
Hypercalcaemia and increased alkaline phosphatase
Leucopenia
TSH receptor antibody (TRAb, 70-100%), anti-TPO antibody (70-80%)
What are some signs of Grave’s disease?
Pretibial myxoedema, thyroid acropachy, thyroid bruit (associated with large goitres, heard over thyroid)
What are some features of Grave’s eye disease?
Occurs in 20%, associated with smoking, TRAb driven, can precede Grave’s diagnosis, can be unilateral, usually mild but can be sight-threatening, mild treated topically, severe may need surgery or steroids
What are some features of nodular thyroid disease?
Older patients, more insidious onsets, thyroid may feel nodular, asymmetric goitre
What are some investigations for nodular thyroid disease?
Increased fT4/3, decreased TSH, antibody negative, high uptake on scintigraphy, USS
What is thyroid storm?
Medical emergency = severe hyperthyroidism
Respiratory/cardiac collapse, hyperthermia, exaggerated reflexes
How is thyroid storm treated?
May require mechanical ventilation
Lugol’s iodine or glucocorticoids
What patients suffer from thyroid storm?
Typically hyperthyroid patients with acute infection/illness or recent thyroid surgery
What are some treatments for hyperthyroidism?
Anti-thyroid drugs (ATDs), beta blockers, radioiodine, thyroidectomy
How do anti-thyroid drugs work?
Inhibit TPO thereby blocking thyroid hormone synthesis
What are some examples of anti-thyroid drugs?
Carbimazole, propylthiouracil (PTU)
What are some features of carbimazole?
First line drug, once daily, risk of aplasia cutis in early pregnancy
What are some features of propylthiouracil?
Only first line in the first trimester of pregnancy, twice daily, inhibits DIO1, 10x less potent than carbimazole
How are anti-thyroid drugs used to treat Grave’s disease?
Dose titration (12-18 months) or block and replace (6 months), 50% relapse
What are the side effects of anti-thyroid drugs?
Generally well tolerated. 1-5% develop allergic-type reactions, fulminant hepatic failure and cholestatic jaundice with PTU use, agranulocytosis
What are some features of agranulocytosis?
ATD cant be used again, highest risk in first six weeks
How are beta blockers used to treat hyperthyroidism?
Useful for immediate symptom relief, reduce activity of sympathetic nervous system, propranolol is drug of choice (also blocks DIO1), caution in asthmatics
How is radioiodine used to treat hyperthyroidism?
1st choice treatment for relapsed Grave’s and nodular thyroid disease, high risk of hypothyroidism when used in Grave’s disease
When is radioiodine contraindicated?
Pregnancy
Active thyroid eye disease = can be used with steroid cover
When is a thyroidectomy indicated, and what are the risks?
When radioiodine is contraindicated
Risks = recurrent laryngeal nerve palsy, hypothyroidism, hypoparathyroidism
What is thyroiditis?
Inflammation of thyroid = Hashimoto’s, DeQuervain’s/subacute, postpartum, drug-induced (amiodarone), acute suppressive thyroiditis
What are some features of subacute thyroiditis?
More common in females, age 20-50 years, may be triggered by viral infection, usually self-limiting
What are the symptoms of subacute thyroiditis?
Neck tenderness, fever, other viral symptoms
Scintigraphy shows slow uptake
How does amiodarone cause thyroiditis?
TFTs abnormal in 50% = inhibition of DIO1 (increased fT4, decreased fT3, normal TSH)
What are the features of the hypothyroidism and hyperthyroidism that can occur in amiodarone-associated thyroiditis?
Hypo = occurs in 13%, associated with iodine rich areas Hyper = occurs in 2%, associated with iodine deficient areas, type 1 (similar to Grave's), type 2 (destructive) or mixed
What is the characteristic of subclinical thyroid disease?
Abnormal TSH with normal thyroid hormone levels
What are the features of subclinical hypothyroidism?
Increased TSH, risk of progression to overt hypothyroidism, higher risk if strongly TPO antibody positive, treat is TSH >10, always treat in pregnancy
What are the features of subclinical hyperthyroidism?
Decreased TSH, risk of progression to overt hyperthyroidism, often seen in multinodular goitre
What is the other name for non-thyroidal illness?
Sick euthyroid syndrome = refers to impact of intercurrent illness on the HPT axis
What patients typically suffer from non-thyroidal illness?
Unwell hospitalised patients
What are the features of non-thyroidal illness?
TSH typically suppressed initially then rises during recovery = avoid checking TFTs in unwell patients unless clinical suspicion of thyroid disease
