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Thyroid Flashcards

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1
Q

Thyroid hormones pathway

A

TRH from hypothalamus stimulates anterior pituitary
Anterior pituitary produces TSH
TSH stimulates T3 and T4 (5x less active), majority produced is T4 as 85% of T3 production is from peripheral T4 conversion
Majority of T4 and T3 bound to thyroxine-binding globulin
Unbound T3 + T4 are active forms, inc cell metabolism + catecholamine effects via nuclear receptors

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2
Q

Factors increasing TBG (and therefore total T3+T4)

A

Pregnancy
Oestrogen therapy (HRT, oral contraceptives)
Hepatitis

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3
Q

Factors decreasing TBG

A 
Nephrotic syndrome
Malnutrition
Drugs (Androgens, corticosteroids, phenytoin)
Chronic liver disease
Acromegaly
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4
Q

Hyperthyroidism test results

A

Increased T4, only ~1% have increased T3

Decreased TSH, unless rare TSH-secreting pituitary adenoma

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5
Q

Hypothyroidism test results

A

Ask only for T4 and TSH, T3 adds nothing

TSH varies through day, trough at 2pm and 30% higher during darkness so test at same time

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6
Q

TFTs in systemic disease

A

Euthyroid but everything low

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7
Q

What is assay interference in TFTs

A

Abs in serum interfering with test

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8
Q

What is thyroid autoantibody test

A

Anti-thyroid peroxidase (TPO) increased in Hashimoto’s/ Graves

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9
Q

What TSH receptor antibody test

A

May be increased in Graves, useful in pregnancy

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10
Q

What is serum thyroglobulin test used for

A

Monitoring treatment of carcinoma

Detection of self-medicated hyperthyroidism where it is low

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11
Q

What is thyroid US used for

A

Distinguishing cystic from solid nodules

If solitary/dominant large nodule in multinodal goitre, do fine-needle aspiration looking for thyroid cancer

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12
Q

Thyroid isotope scan use

A

123-Iodine often used
Useful for determining hyperthyroidism cause + detect retrosternal goitre/ ectopic thyroid tissue/ thyroid metastases (+ whole body CT)
If increased or neutral isotope uptake, unlikely to be malignant, if decreased then 20% chance of malignancy

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13
Q

Thyroid tissue surgery indications

A 
Rapid growth
Compression signs
Dominant nodule on scintigraphy
Nodule ≥3cm
Hypo-echogenicity
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14
Q

Which pt to screen for thyroid abnormalities

A

AF
Hyperlipidaemia

DM (yearly)
Pts with Down’s, Turner’s or Addison’s (yearly)

Women with T1DM during 1st trimester and post delivery

Pts on amiodarone/ lithium 6mthly

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15
Q

What is thyrotoxicosis

A

Clinical effect of excess thyroid hormone

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16
Q

Thyrotoxicosis presentation

A

Diarrhoea, weight loss (if very high paradoxical gain in 10%), appetite inc
Over-active, sweats, heat intolerance
Palpitations, tremor, irritability
Fast pulse, moist warm skin

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17
Q

Thyrotoxicosis tests

A 
Decreased TSH, inc T4/T3
May be mild normocytic anaemia + mild neutropenia
Raised ESR, Ca and LFT
Check thyroid autoAbs
Isotope scan if cause unclear
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18
Q

Thyrotoxicosis causes

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A 
Graves' (2/3 of cases)
Toxic multinodule goitre 
Toxic adenoma (solitary 'hot' nodule producing T3/4)
Ectopic thyroid tissue
Exogenous (iodine excess, levothyroxine excess)
Subacute de Quervain's
Amiodarone, lithium (hypo more common)
Postpartum
TB (rare)
19
Q

Graves’ disease pathology

Study These Flashcards
A

IgG stimulates thyrotropin receptors

20
Q

Toxic multinodule goitre features

Study These Flashcards
A

Seen in elderly/iodine deficient areas
Nodules secrete T3/4
Surgery if dysphagia/ dyspnoea

21
Q

Ectopic thyroid tissue causes

Study These Flashcards
A 
Metastatic follicular thyroid cancer
Struma ovarii (ovarian teratoma with thyroid tissue)
22
Q

What is subacute de Quervain’s thyroiditis

Study These Flashcards
A

Self-limiting post viral with painful goitre

23
Q

Subacute de Quervain’s thyroiditis treatment

24
Q

Thyrotoxicosis drug treatment

Study These Flashcards
A

Beta-blockers (propranolol 40mg/6h) for rapid control
Carbimazole 20-40mg/24h PO for 4wks, reduce according to TFTs every 1-2mths
OR Carbimazole + levothyroxine simultaneously
In Graves maintain for 12-18mths then withdraw, 50% relapse
If relapse then radioiodine or excision

25
Carbimazole SE
Agranulocytosis, can lead to dangerous sepsis | Warn pt to stop and get urgent FBC if infection signs
26
Thyrotoxicosis further treatment (drugs ineffective)
Radioactive 131-Iodine, most become hypothyroid post treatment, CI in pregnancy/ lactation Thyroidectomy (usually total), pts become hypo post treatment again, risk of recurrent laryngeal damage + hypoparathyroidism
27
Thyrotoxicosis complications
Heart failure Angina AF Osteoporosis Gynaecomastia Opthalmology Thyroid storm
28
Eye problems in Graves
Exopthalmos (proptosis) Eyelids retracted from iris exposing sclera Diplopia (can be corrected with Fresnel prism in one lens of spectacle)
29
Thyroid eye problem treatment
Supportive and underlying cause If severe, IV methylprednisolone (best) or prednisolone 100mg/day PO, decreasing according to symptoms Surgical decompression if sight-threatening disease or cosmesis
30
Causes of goitre
``` Diffuse: Physiological Graves Hashimoto's Subacute de Quervain's (painful) ``` Nodular: Multinodular goitre Adenoma Carcinoma
31
Hypothyroidism signs
``` BRADYCARDIC Reflexes relax slowly Ataxia Dry hair Yawning Cold hands Ascites ± non-pitting oedema Round puffy face Defeated demeanour Immobile ± ileus CCF ```
32
Hypothyroidism diagnosis
TSH ≥4mU/L (unless rare 2˚ hypothyroidism, then decreased) depending on pt Decreased T4 Cholesterol + triglyceride increased Macrocytosis (less common is normocytic anaemia)
33
Causes of 1˚ autoimmune hypothyroidism
Primary atrophic hypothyroidism - common, lymphocytic infiltration causes atrophy of thyroid so no goitre Hashimoto's - lymphocytic + plasma cell infiltration so goitre, very high Ab titre
34
1˚ non-autoimmune hypothyroidism causes
Iodine deficiency Post-thyroidectomy/ radioiodine treatment Drug-induced (anti-thyroid drugs, amiodarone, lithium, iodine) Subacute thyroiditis - temp hypo after hyper phase
35
Hypothyroidism associations
``` Autoimmune disease (T1DM, Addison's, pernicious anaemia) Turner's, Down's, CF Genetic conditions (Pendred's if with deafness) ```
36
Hypothyroid pregnancy problems
``` Eclampsia Anaemia Prematurity/ dec birth weight Still birth Post-partum haemorrhage ```
37
Hypothyroid treatment
In healthy + young: levothyroxine (T4) 0-100mcg/24h PO, check TSH 6wkly until normal then yearly Elderly/ischaemic heart disease: 25mcg/24h dose then inc 25mcg/4wks as needed If diagnosis unsure stop T4 and check TSH in 6wks
38
Amiodarone thyroid problems
Can cause hypo as is iodine rich, iodine excess inhibits T4 release Can cause thyrotoxicosis from a destructive thyroiditis T1/2 of amiodarone is ~80d so symptoms continue after drug stopped
39
Myxoedema coma
Hypothyroid coma before death
40
Thyroid receptor processes influenced
Metabolism of substrates, vitamins, minerals Modulation of all other hormones and target-tissue responses Stimulation of O2 use and generation of metabolic heat Protein synthesis + carb/lipid metabolism regulation Stimulation of co-enzyme + related vitamin demand
41
Subclinical hypothyroidism clinical features
TSH>4mU/L with normal T4 and T3 | No symptoms
42
Subclinical hypothyroidism management
Confirm raised TSH is persistent in 2-4mths Recheck history and discuss treatment if non-specific effects affecting pt life Treat if TSH≥10; +ve thyroid autoAbs; past Graves'; other organ-specific autoimmunity
43
Subclinical hyperthyroidism clinical features
Low TSH, normal T3 + T4 | 41% increase in relative mortality from all causes vs euthyroid
44
Subclinical hyperthyroidism management
Confirm suppressed TSH is persistent Check for non-thyroid cause (pregnancy, pituitary/ hypothalamic insufficiency, TSH-suppressing medication (thyroxine, steroids)) If no symptoms, recheck 6mthly Carbimazole or propylthiouracil if symptoms + TSH<0.1

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