Thyroid Disease Flashcards
1
Q
describe the structure of the thyroid
A
- Two Lobes & Isthmus
- Normal weight is around 10-20g, and it is impalpable
2
Q
What is the blood supply of the thyroid gland
A
Arterial supply from the superior and inferior thyroid arts
3
Q
What cells is the thyroid gland made out of
A
- Follicular cells arranged around colloid pool
- C cells – calcitonin producing
4
Q
where are the parathyroid glands
A
- on the back of the thyroid
- 4 parathyroids glansd
5
Q
What do C cells produce
A
Calcitonin
6
Q
Describe how thyroid hormone is made
A
- thyroid is the only part of the body that can concentrate iodine
- iodine within the blood vessel is imported into the follicular cell via the sodium iodine transporter
- it is transfered through the cell and into the follicular lumen with the colloid
- at the same time as that the ER makes a protein called thryoglobulin which is passed into the colloid
- whilst bound to thyroglobulin the amino acid tyrosine has idoines added to it by the enzyme TPO
- the tyrosine has 4 iodine added to it to generate T4
- T4 is then passed back through the cell and is excreted into the blood stream
- carried in the blood where it is bound in the albumin
7
Q
What is the main active thyroid hormone
A
T3
8
Q
Where does conversion to T3 from T4 take place
A
- It takes place in the cell where the thyroid hormone is acting
- this occurs via deiodinases
9
Q
How is the thyroid hormone controlled
A
Via positive and negative feedback loop
10
Q
Describe the feedback loop for thyroid hormones
A
- Hypothalamus releases TRH
- TRH acts on the pituitary
- pituitary releases TSH
- TSH acts on the thyroid gland to release T3 and T4
- T3 and T4 negatively feedback on the pituitary and TSH and the hypothalamus and TRH
11
Q
What happens in graves disease
A
- TSHR antibody
- binds to the TSH receptor and stimulates its activity producing T3 and T4
- leadS to hyperthyroidism
12
Q
Thyroid hormones have major …
A
Thyroid hormones have major importance in neural development in the fetus
13
Q
What are the symptoms of thyrotoxicosis
A
- diarrhoea
- weight los s
- increased appetite
- restlessness
- sweats
- heat intolerance
- palpations
- tremor
- irritability
- laudable emotions
- oligomenorrhoea and infertility
- loss of libido
14
Q
What drug history can lead to thyrotoxicosis
A
- amiodarone - contains a large amount of iodine
- lithium - interfers with iodine
- interferon
- retrovirals
15
Q
What signs do you see on examination with thyrotoxicosis
A
- Fast/irregular pulse (e.g. AF)
- Warm moist skin
- fine tremor
- palmar erythema
- thin hair
- lid lag
- lid retraction (exposure of sclera above iris causing stare)
- goitre or thyroid nodules
- thyroid bruits
16
Q
What investigations do you do in thyrotoxicosis
A
Thyroid Function Tests (TFTs)
In thyrotoxicosis it will show:
- Raised free T4 and T3
- Suppressed TSH
- Thyroid antibodies positive in Graves
- Gastric Parietal cell antibodies often a marker of autoimmune disease
17
Q
What can cause thyrotoxicosis
A
- Graves’ Disease
- Toxic Multi-nodular goitre
- Toxic adenoma
- Destructive thyroiditis
- Excess Iodine (Jod-Basedow)
- Drugs – eg amiodarone / lithium
- Thyroid Hormone Resistance
- TSH producing pituitary tumour (rare) – secondary hyperthyroidism – raised TSH and FT4
18
Q
How do you define graves disease
A
Autoimmune condition causing one or more of:
• Thyroid dysfunction (thyroid stimulating antibodies)
• Opthalmopathy
• Pre-tibial myxoedema
• Acropachy
Characterised by IgG autoantibodies that bind to and activate TSH (thyrotropin) receptors, causing smooth thyroid enlargement and thyroid hormone production, and react with orbital autoantigens
19
Q
What can trigger graves disease
A
- stress
- infection
- childbirth
20
Q
What should you find in graves disease
A
- Diffuse smooth goitre with a bruit
• Often a family history
• Other autoimmune disease may accompany – eg. Type 1 diabetes, Addisons’, Hypoparathyroidism, Premature Ovarian Failure
• Thyroid stimulating antibodies characteristically present
21
Q
What antibodies do you find in graves disease
A
Thyroid stimulating antibodies
22
Q
What do you find in graves eye disease
A
- often a smoker
- painful
- tearful and grittiness
- dipoloppia
- visual acuity reduced
- loss of colour vision
- redness
- proptosis
- Lid lag and retraction
23
Q
What are the investigations you should do in graves ophthalmology
A
MRI orbits
TFTs
24
Q
What is the treatment of graves eye disease
A
Can be sight threatening, so steroids, radiotherapy or surgery may be required
25
Why does colour vision and visual acuity decreases or is lost in graves eye disease
- the fact that the muscle and fat behind the eye causes stretching of the optic nerve
- at the apex of the orbit of the eye there is less space for the nerve and the muscle and the nerve can be compressed
26
graves pre tibial myxoedema is...
rarer than graves eye disease
27
What forms can graves pre-tibial myxoedema take on
- dark plaques
- lymphoedeamtous
- fairly nasty dermatopathy
28
What is the treatment of thyrotoxicosis
Medicines
- Carbimazole
- Propylthiouracil
- Propranolol - may hlep wiht symptoms
radioiodine
Surgery
29
What are the side effects of carbimazole
- rash occurs in 1 in 100,
- agranulocytosis 1 in 1000
- warn about sore throat - if they get a sore throat they need to stop taking the tablet and get an FBC
30
How is radioiodine a treatment for thyrotoxicosis
- I-131 - destroys the gland
- Ablates thyroid and can cure disease, but concerns over radiation exposure to children and close contacts, subsequent hypothyroidism and need for thyroxine, worsening of thyroid eye disease
• Used in relapsed disease when carbimazole fails to cure
31
What is hypothyroidism
- the clinical effect of lack of thyroid hormone
32
What symptoms do you find with hypothyroidism
- tiredness - sleepy, lethargic
- weight gain
- reduced appetite
- cold intolerance
- constipation
- menorrhagia
- hoarse voice
- impaired memory and cognition
- dementia
- myalgia
- cramps
- weakness
33
What are the signs of hypothyroidism
```
BRADYCARDIC
- Bradycardia
- Reflexes relax slowly
- Ataxia (cerebellar)
- Dry thin hair/skin
- Yawning/drowsy/coma
- Cold
Ascites +/- non-pitting oedema +/- pericardial or pleural effusion
- Round puffy face/double chin/obese
- Defeated demeanour
- Immobile
- CCF
```
also
- neuropathy
- myopathy
- goitre
34
What are the severe symptoms of hypothyroidism
- coma
| - hypothermia (Myxoedema Coma)
35
What are the causes of hypothyroidism
* Iodine deficiency - commonest cause
* Hashimoto’s thyroiditis
* Congenital hypothyroidism (1 in 4000)
* Iatrogenic
* Post-partum thyroiditis
36
What is the commonest cause of hypothyroidism
• Iodine deficiency - commonest cause
37
What is cretinism
- Congenital hypothyroidism
38
What is the treatment of hypothyroidism
Treat with levothyroxine – titrated to target TSH (aim for normal range)
39
What is a high TSH with a normal TH4 due to
- intercurrent illness
- inadequate dose
- malabsorption
- poor concordance with therapy
40
if someone has been hypothryoid for a long time what do you want to do
- want to gently introduce thyroxine
| - don't want to give a high dose straight away as can alter metabolic rate and be dangerous
41
What is the history of a multinodular goitre
```
- lump in neck (how fast is it growing?)
• any symptoms of thyrotoxicosis?
• dysphagia
• cough / dyspnoea / stridor
• sudden enlargement or pain
```
42
What would you find of examination of a multinodular goitre
* size
* retrosternal extension (percuss over sternum)
* thyroid status
* signs of airway compromise
43
What is the investigations of a multi-nodular goitre
* Thyroid function test
* Lung function – signs of tracheal compression
* CXR +/- thoracic inlet views
* Ultrasound scan +/- fine needle aspiration
* CT (without contrast)
44
Why do you not give CT contrasted to someone with a multi-nodular goitre
if you give a contrasted CT (contains iodine) to someone with a multinodular goitre you are going to introduce thyrotoxcosis
45
What is the treatment of a multinodular goitre
• Surgery vs RadioIodine
46
What is the history of thyroid neoplasia
• Neck lump / swelling – rate of change
47
How do you investigate a thyroid neoplasia
* Ultrasound scan +/- Fine Needle Aspiration
* Consider checking calcitonin levels – elevated in medullary cancer of the thyroid
* Chest XR
48
What surgery can you do on a thyroid neoplasia
* Diagnostic hemithyroidectomy
| * Near-total thyroidectomy
49
What treatment can be used for a thyroid neoplasia
* Near-total thyroidectomy helps to confirm histology – whether papillary / follicular cancer
* Adjunctive therapy - Iodine 131 ablation
* Therafter - suppressive thyroid replacement – ie high dose thyroxine to suppress TSH and reduce chance of recurrence
* External beam radiotherapy also given
* Serum thyroglobulin is a useful tumour marker – rising levels may indicate recurrence
* Iodine tracer scan may also be useful for monitoring
50
what is the drainage of the thyroid gland
- Superior and middle thyroid veins = these drain into the IJV
- inferior thyroid vein = these drain into the brachiocephalic vein
51
What two cells make up the thyroid gland
- follicular cells
| - parafollciular cells (C cells)
52
What does follicular cell produce
T3 and T4
53
What surrounds the thyroid
- encapsulated in pretracheal fascia
| - covered by infra hyoid strap muscles
54
What increases and decreases the level of TBG (thyroxine binding globulin)
- TBG is increased by pregnancy as oestrogen inhibits hepatic breakdown
- TBG is decreased by liver failure
55
why in pregnancy is there normal T3/T4 despite the increase in TBG
- there is an increase in TBG in pregnancy bu there is normal free T3/T4 because of a increase in the total amount of T3/T4 due to normal physiological negative feedback
56
what do T3/T4 bind to
TBG. - thyroxine binding globulin
57
T4 has less...
potency than T3
58
what increases T4 being converted to T3
- increased in obesity
59
What decreases T4 being converted into T3
- pregnancy
- fasting
- stress
- hepatic failure
- renal failure
- beta blockers
60
What does TSH do
- increases production of T4/T3
- hypertrophy and hyperplasia of thyroid follicular cells
- increases blood flow to the thyroid
61
what does T3 and T4 do
1. BMR - increases sodium and potassium ATPase activity to increase oxygen production and heat
2. Metabolism
- increase in glucose uptake and absorption
- increase glycogenolysis
- increase gluconeogensis
- increase insulin
- increase FA oxidation
- decrease cholesterol in plasma
- decrease muscle mass
3. Cardiorespiratory
- increase in HR and CO
- increase in vasodilation
- increase in ventilation
4. CNS
- increase SNS activity
- affects mental state - hyper anxiety, hyper nervousness, hypo sluggishness
5. Skeletal
- increase growth plate chondrocytes and osteoblasts
- increase in osteoclast activity (in thyrotoxicosis leads to osteoporosis)
6. Reproductive
- thickens endometrium in females
- hypothrlydoism associated with infertility
Development
- potentiates growth
- potentiates foetal and neonatal brain development
62
What does it mean when
- TSH raised
- T4 reduced
hypothrlydoism
63
What does it mean when
- TSH raised
- T4 normal
treated hypothyroidism or subclinical hypothyroidism
64
What does it mean when
- TSH raised
- T4 raised
- TSH-secreting tumour or thyroid hormone resistance
65
What does it mean when
- TSH lowered
- T4 raised
- T3 lowered
- slow conversion of T4 to T3 ( deiodeinase deficiency; euthyroid hyperthyroxinaemia) or thyroid hormone antibody artefact
66
What does it mean when
- TSH decreased
- T4 increased
hyperthyroidism
67
What does it mean when
- TSH decreased
- T4 normal
subclinical hyperthyroidism
68
What does it mean when
- TSH lowered
- T4 lowered
- central hypothyroidism
69
What does it mean when
- TSH lowered
- T4 lowered
- T3 lowered
- sick euthryoidism or pituitary disease
70
What does it mean when
- TSH normal
- T4 abnormal
- consider changes in TBG, assay interference, amiodarone or pituitary TSH tumour
71
What can cause thyrotoxicosis not associated with hyperthyroidism
- thyroiditis - drug induced (e.g. amiodarone), silent De Quervain's (tender goitre exclusively), Subacute (postpartum), radiation induced
- exogenous thyroid hormones - over treatment, food contamination with iodine
- Ectopic thyroid tissue - metastatic thyroid carcinoma, struma ovarii (ovarian teratoma with thyroid tissue)
72
What is graves ophthalmopathy
- auto-antibody cross-reaction with orbital autoantigens
73
What are symptoms of graves ophthalmopathy
- eye discomfort
- grittiness
- increase tear production
- photophobia
- diplopia
- decrease acuity and colour vision
74
What are the signs of graves ophthalmopathy
- exophthalmos - appearance of protruding eye
- proptosis - eyes protrude beyond the orbit
- ophthalmoplegia
- afferent pupillary defect - sign of optic nerve compression
- conjunctival oedema
- corneal ulceration
- papilloedmea
75
what are the risk factors for graves ophthalmopathy
- smoking
| - radioiodine therapy
76
What is the management for graves ophthalmopathy
1. treat underlying cause
2. mild - artificial tears, elevation of head at night, sunglasses, avoid dust
3. Severe - steroids, surgical decompression
77
What makes up graves dermopathy
1. pretibial myxoedema - oedematous swellings above lateral malleoli
2. thyroid acropachy - extreme manifestation with clubbing, painful finger and toe swelling and periosteal reaction in limb bones
78
toxic adenoma and multinodular goitre are both...
TSH independent
79
What is a toxic adenoma
- solitary focal, diffuse hyperplasia of follicular cells that secrete thyroid hormones
80
What is a toxic multi nodular goitre
- most common cause of thyrotoxicosis in iodine-deficient areas
- also seen in elderly patents
- nodules secrete excess thyroid hormones
81
What is thyroiditis
- this is when hormone synthesis is not increased but instead there is destruction of thyroid follicular cells resulting in a transient increase in thyroid hormones
- once they are exhausted the patient becomes hypothyroid
82
What are thyroid cysts
- benign solitary nodules that creates pressure symptoms
- can be painful if it bleeds
- need to aspirate or excise
83
What does subclinical hyperthyroidism look like
- normal T3 and T4 but suppressed TSH
84
What are the endogenous causes of subclinical hyperthyroidism
- toxic adenoma
| - multinodular goitre
85
What are the exogenous causes of subclinical hypothyroidism
- levothyroxine
86
What happens in thyroid hormone resistance
- mutation in receptor at pituitary gland
| - rise in T3 and T4 fails to suppress TSH
87
what is the difference between primary and secondary hyperthyroidism
Primary Hyperthyroidism
- Low TSH
- high T4 or T3
Secondary hyperthyroidism
- high TSH
- High T4
88
What investigations would you carry out for hyperthyroidism
TFTs - free T3+T4 and TSH levels
- Anti-TSH and anti-TPO antibodies
- Radioiodine uptake – indicates synthesis of thyroid hormones in the tissue
- USS – differentiate cysts vs. solid nodules
- Fine Needle Aspiration – diagnosis of malignant nodules
- CT – evaluate extension of thyroid enlargement
- Blood – normocytic anaemia; mild neutropenia (Graves’); ↑ESR, calcium, LFTs
89
Patients with multi nodular goitre always...
relapse
90
What is management of hyperthyroidism
Medical
- beta blockers - to control symptoms
- carbimazole
- Propylthiouracil
Radioactive idoine
Thyroidectomy
91
what are the ways in which you can give carbimazole
- Titration: Carbimazole 20-40mg/24 hour PO for 4 weeks reduce according to TFTs every 1-2 months
- block replace: give carbimazole and levothyroxine simultaneously (less chance of iatrogenic hypothyroidism)
have to maintain either regimen 12-18 months then withdraw
92
What are the side effects of carbimazole
- agranulocytosis - decreased neutrophils can lead to infection and sepsis
93
When would you give propythiouracil
- first trimester of pregnancy
- thyroid storm
- carbimazole CI
94
When is radioactive iodine used
- multinodular goitre
- toxic adenoma
- carbimazole-relapsed graves
95
What are the contraindications for radioactive iodine
- pregnancy
- lactation
- graves ophthalmopathy
96
What are the side effects of radioactive iodine
hypothyroidism
97
When does a thyroidectomy take place
- suspected malignancy
| - compressive symptoms
98
What are the complications of a thyroidectomy
- recurrent laryngeal nerve damage
- hypoparathyroidism (lifelong vitamin D supplements)
- local haemorrhage - laryngeal oedema and this leads to stridor which is an emergency
99
what are the complications of hyperthyroidism
- Heart failure – due to thyrotoxic cardiomyopathy, especially in elderly
- Angina
- AF (10-25%) – consider warfarin to prevent VTE
- Osteoporosis
- Ophthalmopathy
- Gynaecomastia
- Thyroid storm
100
What are the precipitants of a thyroid storm
- recent thyroid surgery
- radioiodine therapy
- infection
- MI
- trauma
101
How does a thyroid storm present
- severe hyperthyroidism
- fever
- agitation
- confusion
- coma
- tachycardia
- AF
- D&V
- goitre
- thyroid bruit
- acute abdomen
- heart failure
102
How do you diagnose a thyroid Storm
- do not wait for test results if urgent treatment is needed: do TFTs
103
What is the treatment for a thyroid storm
1. IV access, fluids, NG tube if vomiting
2. Take blood for TSH, T3, T4, cultures (if suspected infection)
3. Sedate if necessary (eg chlorpromazine 50mg PO/IM), Monitor BP
4. Propanolol 60mg/4-6h PO
- Only if no CI and CO normal
- Asthma/↓CO: can cause cardiac arrest – consider ultra-short-acting beta-blockers, eg IV esmolol
- Consider diltiazem if beta-blockers CI + get help
5. High-dose digoxin may be needed to slow the heart
6. Antithyroid drugs: carbimazole 15-25mg/6h PO (or via NGT) + after 4h give Lugol’s (iodine) solution 0.3ml/8h PO to block thyroid
7. Hydrocortisone 100mg/6h IV or Dexamethasone 15-25mg/6h PO – to prevent peripheral conversion of T4 to T3
8. Treat infection if suspected, eg co-amoxiclav 1.2g/8h IV
9. Adjust IV fluids as necessary; cool with tepid sponging ± paracetamol
10. Continuing treatment
- After 5 days reduce carbimazole to 15mg/8h PO
- After 10 days stop propanolol and iodine (Lugol’s) + adjust carbimazole
If there is no significant progress in 24h, thyroidectomy may be an option
104
What is the aim of treatment for a thyroid storm
1. counteracts peripheral effects of thyroid hormones
2. inhibit thyroid hormone synthesis
3. treat systemic complications
105
Name types of thyroid carcinoma
- papillary
- follicular
- medullary
- anapaestic
- lymphoma
106
For papillary thyroid carcinoma what is it
- associated with
- occurs in
- origin
- tumour markers
- spread
- treatment
- prognosis
- Associated with radiation
- Occurs in young people (20-40yrs); more common in females (3:1)
- Origin: follicular cells
- Tumour markers: Ig
- Spread: local to lymphatics, sometimes lung/bone mets
- Tx: total thyroidectomy ± node excision ± radioiodine
- Prognosis: good, especially in young
107
For follicular thyroid carcinoma
- occurs in
- origin
- tumour markers
- spread
- treatment
- prognosis
- More common in females (3:1) and Ages 40-60
- Origin: follicular cells
- Tumour markers: Ig
- Spread: haematogenous to lung/bone
- Tx: total thyroidectomy + T4 suppression + radioiodine
- Prognosis: good if resectable
108
For medullary thyroid carcinoma
- genetics
- occurs in
- origin
- tumour markers
- spread
- treatment
- prognosis
- 30% familial (MEN2)
- Affects young men (40-50yrs)
- Origin: parafollicular cells
- Tumour markers: CEA & calcitonin
- Spread: local and metastases
- Tx: thyroidectomy, node clearance ± radioiodine
- Prognosis: poor, but indolent course
109
For anapaestic thyroid carcinoma
- occurs in
- growth rate
- origin
- spread
- treatment
- prognosis
- Women (3:1), >60yrs
- Rapid and aggressive growth and spread
- Origin: undifferentiated follicular cells
- Spread: locally invasive
- Tx: palliative; can try thyroidectomy ± radioiodine
- Prognosis: very poor
110
for lymphoma thyroid carcinoma
- origin
- treatment
- In situ autoimmune thyroiditis or systemic lymphoma
- Origin: lymphocytes
- Tx: chemotherapy + radiotherapy
111
What are non thyroid neck swellings
- thyroglossal cyst
- branchial cyst
- lymphadenopathy
- pharyngeal pouch
- dermoid cyst
- lipoma
- fibroma
- laryngocele
- salivary gland swelling
- vascular - carotid body or aneurysm
112
What is a goitre
A swelling in the thyroid gland
113
What are the three classifications of goitre
- diffuse - uniform overall enlargement
- nodular - occurs after diffuse; loss of thyroid structure; certain areas become fibroses and underachieve
- malignancy - adenomas/carcinomas felt as a lump
114
Describe the causes of a diffuse goitre
- Simple euthyroid goitre: pregnancy, puberty, no clear cause
- autoimmune thyroid: firm diffuse goitre seen in Hashimotos and Graves'
- thyroiditis - acute pain and tenderness seen in De Quervain's
115
Describe causes of a nodular goitre
- multinodular goitre
| - solitary node - rule out malignancy but normally benign
116
How does iodine deficiency cause goitre
- low iodine leads to hypothyroidism this causes an increase in TSH and growth of the gland forming diffuse goitre
- some areas firbose and a mulitnodular toxic goitre is formed
- this leads to hyperthyroidism
117
How does iodine excess cause goitre
- high iodine can lead to destructive thyroiditis and the release of T4 and T3 this causes hyperthyroidism and may become hypothyroidism after a few months due to depletion and inhibition of deiodinase by drug
118
What is more common hypothyroidism or hyperthyroidism
hypothyroidism
119
What causes primary hypothyroidism
- Primary autoimmune hypothyroidism
- iodine deficiency - worldwide chief cause
- post-thyroidectomy or radio iodine treatment
- drug induced - antithyroid drugs, amiodarone, lithium, iodine
- subacute thyroiditis - temporary hypothyroidism after hyperthyroid phase
120
What causes secondary hypothyroidism
- not enough TSH due to hypopituitarism; very rare
121
what are the two types of primary autoimmune hypothyroidism
- Primary atrophic hypothyroidism
| - Hashimoto's thyroiditis
122
Describe primary atrophic hypothyroidism
- diffuse lymphocytic infiltration of the thyroid which leads to atrophy
123
Describe Hashimoto's thyroiditis
- goitre due to lymphocyte and plasma cell infiltration
- more common in women aged 60-70
- anti-TPO antibodies increase
- may be hypothyroid or euthyroid; rare initial period of hyperthyroid
124
What are associations of hypothyroidism
- the autoimmune conditions
- Turners and down's syndrome
- cystic fibrosis
- ovarian hyperstimulation
- POEMS syndrome - polyneuropathy, organomegaly, endocrinopathy, m-protien band, skin pigmentations
- genetics - dyshormonogensis
125
What can cause a myxoedema coma
- infection
- MI
- stroke
- trauma
- thyroidectomy
- radioiodine
- pituitary surgery
126
what is the presentation of a myxoedema coma
- looks hypothyroid
- aged over 65 years
- hyporeflexia
- hypothermia
- decreased glucose
- bradycardia
- psychosis
- coma
- seizures
127
How do you treat a myxoedema coma
1. Blood – TFTs, FBC, U&Es (often ↓Na+), cultures, cortisol, glucose
2. ABG for PaO2 – high-flow oxygen if cyanosed; ventilation may be needed
3. Correct any hypoglycaemia
4. Give T3 5-20μg/12h IV slowly
- May precipitate ischaemic heart disease; alternative levothyroxine
5. Give hydrocortisone 100mg/8h IV if pituitary hypothyroidism is suspected (ie no goitre, no previous radioiodine or thyroidectomy)
6. If infection suspected, give Abx, eg co-amoxiclav 1.2g/8h IV
7. Caution with fluid, rehydrate as needed by watch for cardiac dysfunction; BP may not respond to fluids and inotropes may be needed
8. Active warming (blankets, fluids) may be needed for hypothermia
9. Further treatment:
- T3 5-20μg/12h IV until sustained improvement (~2-3days) then levothyroxine 50μg/24h PO
- Hydrocortisone + IV fluids as needed
128
What is the management of hypothyroidism in young and healthy patients
- Levothyroxine 50-100μg/daily PO – before breakfast
- Review at 12 weeks
- Adjust every 6 weeks by clinical state and to normalise but not suppress TSH (keep TSH>0.5mU/L)
- Gradual dose increases to prevent arrhythmias and oversensitivity to catecholamines
- T½ ~7 days so wait ~4 weeks before checking TSH to see if a dose change is right
- AIM: TSH 0.5-2.5mU/L (lower ½ of RR) and free T4 ~15-25pmol/L (upper ½ of RR)
- NOTE: small changes in serum free T4 have a logarithmic effect on TSH
- Once normal, check TSH yearly
129
What affects absorption of levothyroxine
Enzyme inducers ↑metabolism of levothyroxine
Iron reduces absorption of levothyroxine, give at least two hours apart
130
What is the management of hypothyroidism in elderly and IHD patients
- Start with levothyroxine 25ug/daily PO
- increase dose by 25ug/4 weeks
- take caution as may precipitate angina or MI
131
How do you manage pregnancy in hypothyroidism
- increase in dose of 25-50ug is often needed to maintain normal TSH levels
132
what are the side effects of hypothyroidism
- hyperthyroidism
- decreased bone mineral density
- worsening of angina
- AF
