Endocrine JC038: I Am Losing Weight And Sweating All The Time: Causes Of Severe Weight Loss: Thyrotoxicosis, Hypothyroidism Flashcards

1
Q

Physiology of the thyroid gland

A

Hypothalamus —> TRH (Thyrotropin-releasing hormone)
—> Pituitary —> TSH
—> Thyroid gland —> Thyroxine (T3, T4)
—> Blood (>99% protein bound)
—> Free T3, T4 (active hormone) inhibit Hypothalamus + Pituitary

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2
Q

***Synthesis and Secretion of Thyroid hormones (T3, T4)

A

Iodine: ingested as iodide in diet
Iodide trapping
—> via Na/I symporter (NIS)
—> oxidised to Iodine by **Thyroperoxidase with H2O2
—> Iodine react with **
Tyrosine (in Thyroglobulin) (Organification: Synthesis of Thyroid hormone) (within Follicular cells)
—> T3, T4 (Iodothyronines: stored in colloid on **Thyroglobulin)
—> secreted into Follicular cells upon stimulation by TSH
—> colloid droplets fuse with lysosomes
—> T3, T4 **
cleaved from Thyroglobulin by Protease in Follicular cells
—> T3, T4 released into circulation

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3
Q

Synthesis of T3, T4

A

Iodide
—(Peroxidase)—> Iodine free radical
—(Peroxidase, added to Tyrosine unit of Thyroglobulin)—> Monoiodotyrosine-Thyroglobulin (MIT-Thyroglobulin) —> DIT-Thyroglobulin

Via Intra/Inter-molecular coupling
DIT + DIT —> T4-Thyroglobulin (Thyroxine)
MIT + DIT —> T3-Thyroglubulin (Triiodothyronine)

  1. Active Uptake of Iodide from blood by ***NIS into Thyrocyte / Follicular cell (basolateral membrane) (向出)
    - cotransport 2 Na ions + 1 Iodide ion
    - Na gradient: Driving force (created by Na/K ATPase: Na pump back to blood)
  2. Efflux of Iodide into follicular lumen via ***Pendrin (apical membrane) (向入)
  3. Iodide **oxidised to Iodine and rapidly organified by incorporation into selected tyrosyl residues of Thyroglobulin
    —> **
    Organification
    —> form mono-iodotyrosine (MIT) + di-iodotyrosine (DIT) on Thyroglobulin
    —> **catalysed by Thyroid peroxidase (with presence of **H2O2)
  4. Coupling reaction
    - T4 formed from 2x DIT
    - T3 formed from MIT + DIT
    —> T3, T4 still attached to Thyroglobulin
    —> stored in follicle as colloid (for ~2-3 months)
  5. T3, T4 liberated from Thyroglobulin scaffold before secreted as free hormone in blood
    —> require endocytosis of Iodinated Thyroglobulin from apical membrane (成舊野食翻落Follicular cell)
    —> ***digestion by Lysosomes (remaining MIT, DIT on Thyroglobulin will be deiodinated intracellularly —> Iodide transported back to colloid via Pendrin for reuse)
    —> free T3, T4
    —> T4&raquo_space;> T3 (40 fold in plasma conc)
  6. Circulating thyroid hormones bind to carrier protein
    - ***Thyroxine-binding globulin (~70%)
    - Albumin (~15%)
    - Transthyretin (~10%)
    - unbound (0.05%)
    —> ensure circulating reserve + delay metabolic clearance of hormone
    —> only unbound hormone are bioavailable
    —> clinical measurement: measure total T4 instead of unbound T4 (in absence of protein binding abnormality) + measure binding protein level

Changes in binding protein level:
1. ↑ binding protein —> ↓ free thyroid hormone —> stimulate TSH release
2. ↓ binding protein (chronic liver disease) —> ↑ free thyroid hormone —> suppress TSH release —> ↓ thyroid hormone synthesis and release

  1. Active biological half life
    - T4: 7 days
    - T3: 1 day
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4
Q

Thyroglobulin and Thyroperoxidase

A

Thyroglobulin: Backbone protein for making + storage of thyroid hormone
Thyroperoxidase (past: Thyroid microsomal enzyme): Enzyme for organification process for synthesis of thyroid hormone

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5
Q

Mechanism of Thyroxine action

A

T3 (active hormone, secreted by thyroid gland / peripheral tissue (liver) conversion)
—> Active cellular uptake
—> **Intracellular protein receptor (T3>T4)
—> Modulation of nuclear RNA
—> 1. **
Protein synthesis
—> 2. **Mitochondrial oxidative phosphorylation (Metabolism of cells)
—> 3. **
Enzyme synthesis

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6
Q

***Thyroid function test

A
  1. Serum free thyroid hormone fT3, fT4 level (Active hormone)
    - measures unbound free circulating hormone level
    - fT4: 0.02%
    - fT3: 0.2%
    - NOT measure total (bound hormone ∵ fluctuations in binding protein e.g. pregnancy, contraceptive —> causing ↑ total thyroid hormone)
  2. Serum TSH
    - Thyrotoxicosis: Suppressed
    - **Secondary hypothyroidism (hypothalamic-pituitary failure): Low / Normal (∴ sometimes cannot tell whether a patient has hypothyroidism just by TSH)
    - **
    Primary hypothyroidism: Elevated
  3. Serum Total T4
    - measurement of total T4 which is bound to plasma binding proteins (99.96%) (**Thyroid hormone-binding globulin TBG, **Thyroxine-binding prealbumin TBPA)
    - affected by disease state which alters TBG level e.g. ↑ in pregnancy, ↓ in hypoalbuminaemia (chronic liver disease)
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7
Q

Screening for Thyroid Dysfunction

A

Serum TSH (may miss unusual patient with secondary hypothyroidism with normal TSH)
- sometimes must be coupled to T4 for interpretation

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8
Q

Thyroid function testing algorithm (SpC Medicine)

A

Low TSH
—> Increased fT4 —> Hyperthyroid
—> Normal fT4 —> Subclinical hyperthyroidism, T3 thyrotoxicosis, Non-thyroidal illness
—> Decreased fT4 —> Hypopituitarism, Drugs, Non-thyroidal illness

High TSH
—> Increased fT4 —> Pituitary tumour, Thyroid resistance
—> Normal fT4 —> Subclinical hypothyroidism
—> Decreased fT4 —> Hypothyroid

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9
Q

***Signs / Symptoms of Hyperthyroidism

A

Symptoms:
↑ Metabolism + ↑ Sympathetic discharge
1. **Weight loss
2. **
Palpitation
3. Nervousness
4. Easy fatiguability
5. **Excessive sweating
6. **
Heat intolerance
7. Hyperkinesia
8. **Diarrhoea
9. Hair loss
10. **
Eye problem (if ***autoimmune thyroid disease)

Signs (記: 頸, 眼, 皮膚):
1. Goitre

  1. Thyrotoxic eye signs
    - **Lid lag, retraction (ALL causes of hyperthyroidism)
    Specific to Grave’s (self notes):
    - **
    Periorbital edema
    - **Exophthalmos (Proptosis)
    - **
    Extraocular muscle involvement —> Limitation in rotation of eyeballs —> Diplopia (∵ infiltration of retroorbital tissue, ∵ inflammation of retroorbital eye muscles)
    - **Corneal involvement e.g. Corneal erosion (∵ failure of covering of eyes)
    - **
    Sight loss (∵ traction of optic nerve)
  2. Skin (if autoimmune thyroid disease)
    - Pretibial myxoedema (non-tender, thickening, swelling, redness, hairy, pigmentation (may confuse with cutaneous polyarteritis nodosa), stop above ankle)
    - ***Thyroid acropachy (autoimmune involvement, infiltration of soft tissue around nail bed —> finger clubbing)
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10
Q

***Causes of Thyrotoxicosis

A
  1. ***Graves’ disease (most common)
  2. ***Toxic MNG (middle age / older)
  3. ***Toxic adenoma (benign tumour)
  4. ***Thyroiditis (release of pre-formed hormone into bloodstream)
  5. ***Pituitary hyperthyroidism (presence of TSH-secreting pituitary adenoma)
  6. Molar hyperthyroidism (∵ multiple pregnancy, hyperemesis gravidarum during 1st trimester, struma ovarii, molar pregnancy)
  7. Factitious (takes too much / overdose of thyroid hormone)
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11
Q

Graves’ disease

A

Autoimmune disease
- lymphocytes acting against self-antigen: TSH receptor

***Thyrotropin-receptor Ab (TRAb) (aka TSH-receptor Ab) stimulates TSH receptor on Thyroid gland —> stimulates Thyroid gland
1. Stimulates thyroid cell hyperplasia
2. Increase thyroid hormone release
—> Hyperthyroidism —> Suppress TSH release from pituitary

Epidemiology:
- M:F = 1:4.8
- Highest incidence: Reproductive age (20-50)

Clinical diagnosis:
1. **Diffusely enlarged thyroid gland (x nodular)
2. ↑ fT3, fT4 but ↓ TSH level
3. **
Diffuse ↑ uptake on radioiodine scintillation scan
4. ***Positive TSH receptor Ab in blood

Clinical presentation:
1. Goitre
2. Hyperthyroidism symptoms
3. **Exophthalmos (70%)
4. **
Pretibial myxoedema (a few %) (specific for Graves, can be present on for dorsum as well (SpC Medicine))
5. **Related autoimmune disease (a few % e.g. MG, insulin dependent DM)
6. Complications of hyperthyroidism
- **
Thyroid storm (severe hyperthyroidism)
- **Thyrotoxic periodic paralysis associated with **hypokalaemia
- **AF
- **
Heart failure

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12
Q

Radioisotope Thyroid Scan

A

Find out underlying cause for Hyperthyroidism

↑ Uptake:
1. Graves’ disease: **Diffuse uptake
2. MNG: **
Heterogeneous uptake
3. Toxic adenoma: **Focal area of ↑ uptake with ↓ uptake in rest of gland
4. TSH-secreting pituitary adenoma: **
Diffuse uptake (TSH: high / normal differentiate from Graves’: TSH suppressed)

↓ Uptake:
1. **Thyroiditis
2. **
T4 overdose
3. Iatrogenic overuse of thyroid hormone

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13
Q

Clinical usefulness of TRAb

A
  1. Establish diagnosis of Graves’ disease
    - usually not necessary as ~100% patients with active Graves’ are positive for TRAb
    - level of Ab ↓ with Anti-thyroid drug treatment
  2. ***Prognostic indicator of the outcome of Anti-thyroid drug treatment for Graves’
    - positive TRAb at the end of therapy indicates higher chance of relapse —> should continue treatment
    - negative TRAb more likely to have prolonged remission
  3. Forecasting ***neonatal Graves’ in pregnant woman during 3rd trimester
    - high level of TRAb associated with neonatal Graves’ due to transplacental passage of Ab
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14
Q

***Management of Graves’ disease

A
  1. Anti-thyroid drugs
    - Thiouracil derivatives (**Thionamides): Carbimazole, Methimazole, Propylthiouracil (PTU) (PTU shorter t1/2)
    —> duration: **
    12-18 months (treat until TRAb **negative)
    —> +/- T4 supplement (Block and Replace)
    —> major drawback: **
    >60% relapse
  • ***Lithium
    (—> made use of hypothyroidism SE: Nephrogenic DI (SpC Medicine))
    —> block Na-I transporter
    —> monitor carefully
    —> only use if patient sensitive to Thiouracil derivatives
  1. Surgery
  2. Radioactive iodine therapy
  3. Ancillary drug therapy
    - Sedatives
    - **β-blockers
    - **
    Iodide (Lugol’s solution)
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15
Q

Indications of Definitive treatment (RAI / Surgery) over Medical treatment (Metabolic round)

A
  1. Concomitant heart conditions (e.g. HF, AF) —> Relapse from medical treatment can cause decompensation of heart conditions
  2. GO (avoid RAI since can exacerbate GO)
  3. Thyrotoxic Periodic Paralysis (TPP)
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16
Q

Thiouracil derivatives

A

MOA:
1. Inhibit ***Thyroid hormone synthesis
- inhibit organification of iodide to iodine
- inhibit coupling of iodotyrosines

  1. Inhibit ***T4 to T3 conversion (PTU only)
  2. ***Immunosuppressive effect
    - action on intrathyroid antigen-presenting cells —> ↓ Thyroid AutoAb level

Absorption of PTU / Methimazole (Carbimazole converted to Methimazole in body)
- unrestricted
- actively concentrated by thyroid gland within minutes
- long t1/2 esp. Methimazole (can be given as QD dose)
- **PTU shorter t1/2
- **
Pregnancy / Breastfeeding: **PTU preferred ∵ cross placenta less than Methimazole
- both transferable into milk (Methimazole > PTU)
- **
Teratogenic: Methimazole / Carbimazole&raquo_space; PTU: Aplasia cutis, **Choanal atresia —> using lowest possible dose
- use PTU from pre-conception until end of **
1st trimester —> switch to Methimazole/ Carbimazole (less ***liver SE) in 2nd trimester

SE:
1. Rash (5%)

  1. **Agranulocytosis (0.1%)
    - **
    Idiosyncratic (SpC Medicine)
    - Genetic predisposition: HLA-B38:02:01
    - occur suddenly
    - reversible
    - usually **
    first 2 months
    - with age (>40)
    - with high dose (∴ lowest possible dose)
    - S/S: fever, sore throat —> quickly go to doctor to check WBC (may need G-CSF)
    - not routinely check CBC, only if deranged LFT / infection (SpC Medicine)
  2. Rare: **Cholestatic jaundice, **Hepatocellular toxicity, Acute arthralgia, ANCA induced vasculitis
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17
Q

Indications for Anti-thyroid drugs

A
  1. Children and adolescents
  2. Pregnant women
  3. Adults
    - esp. mild-moderate gland size + disease activity
    - preference of patient
18
Q

Predictive patient characteristics of response to Anti-thyroid drugs

A

Higher recurrence:
1. Large goitre
2. Positive family history
3. Higher initial T3 / T3:T4 ratio
4. Shorter course of treatment
5. Failure of normalisation of TSH after 1 / 2 years
6. High TRAb level

19
Q

Surgical treatment for Diffuse toxic goitre

A

Definitive treatment

Indication:
- Young age
- **Failed medical treatment
- **
Relapse a few times
- SE of medications
- **Eye signs
- **
Expecting pregnancy
- Refuse radioactive iodine
- ***Big goitre

  1. Bilateral subtotal thyroidectomy
  2. Unilateral total + contralateral subtotal lobectomy
  3. Near total thyroidectomy

**Pre-operative preparation:
1. **
Anti-thyroid medications until **Euthyroid
- avoid precipitation of **
thyroid storm during operation
2. **β-blockers for 2 weeks
(3. Old practice: **
Lugol’s iodine 5 days before operation (↓ vascularity of thyroid —> may ***reduce blood loss during operation))

20
Q

***Complications of Thyroid surgery

A
  1. **Vocal cord dysfunction (unilateral / bilateral)
    - **
    RLN (Infraglottic) / ***External branch of Superior laryngeal nerve (Supraglottic: Cricothyroid)
    - transient / permanent
  2. ***Hypoparathyroidism (∵ injury / removal of parathyroid gland)
    - transient / permanent
  3. Bleeding
    - superficial / deep
  4. ***Tracheomalacia (cartilage in trachea collapses especially during increased airflow)
  5. Wound complications
    - Seroma
    - Hypertrophic scar
  6. ***Thyroid storm
  7. Others

**Post-op Monitoring:
1. Voice
2. **
Ca level (6-12 hours after operation) (Hypoparathyroidism)
3. SOB, Compression sensation
4. ***HR, temperature (Thyroid storm)
5. Infection
6. Keloid scar

21
Q

Radioactive Iodine

A

α-emission of 131-I mostly not absorbed
***β-emission of 131-I almost completely absorbed

MOA:
1. Induce ***necrosis of follicular cells
—> fibrosis
—> disappearance of colloid

  1. Non-destroyed cells have limited replication
  2. Affect thyroid autoimmunity
    - destruction of radiosensitive intrathyroid T-suppression cells
    - but could lead to radiation thyroiditis —> release of thyroid Ag into blood —> **surge of TRAb within first few weeks of radioactive iodine (may have **thyroid eye disease come rapidly)

Use:
- since late 1940
- gradual trend ↑ use
- ↓ age limit esp. in USA

Advantages:
1. **Low relapse rate (15% after 1 dose)
2. Simple + economical
3. No immediate complication (caution with severe cases e.g. **
thyroid storm, thyroid eye disease)

22
Q

Indications for 131-I

A
  1. Adults >30
    - age limit arbitrary
    - except if small gland / mild disease
  2. ***Thyrotoxic heart disease
  3. Relapse after surgery
  4. CI to surgery
23
Q

Preparation and precautions of 131-I therapy (From ERS15)

A

Similar preparation for both Hyperthyroidism and Differentiated thyroid cancer
1. Follow legislation, regulation on safe use of radioisotope therapy

  1. Facilities needed: Trained personnel, storage equipment, radiation protection, waste handling, monitoring, controlling, handling contaminants
  2. Discussion of treatment options, patient’s consent, instruct patient on post-therapy precaution, follow-up
  3. In hyperthyroidism, **Stop anti-thyroid medication 4-14 days before RAI
    - Carbimazole: **
    4 days
    - PTU: **14 days
    —> allow ↑ TSH production from pituitary
    —> **
    ↑ Iodine uptake by residual thyroid tissue / tumour cells
  4. ALL female: ***stop breastfeeding, practice contraception 4 weeks before RAI
  5. ***Low iodine diet for >= 2 weeks
    - avoid seafood, dairy products, soy products, iodine containing medications
24
Q

Complication and Precautions of 131-I

A
  1. Hypothyroidism
    - transient / permanent
  2. Fetal risk (***definite)
    - transient radiation —> induced changes in gametes —> avoid pregnancy for 6-12 months
    - cross placenta + concentrated by fetal thyroid (>12 week) —> CI in pregnancy
  3. Excreted in milk
    - ***NO breastfeeding
  4. **↑ Risk of Thyroid eye disease developing after RAI —> **Avoid RAI in GO
  5. Precipitate **thyroid storm due to **radiation thyroiditis

NB:
- Thyroid carcinoma (NOT ↑ with RAI)
- Leukaemia (NOT ↑ with RAI)
- Transmissible genetic damage (NOT ↑ with RAI)

25
Q

***Thyroid eye disease (TED)

A

Aka ***Graves’ ophthalmopathy (GO), Dysthyroid eye disease

Pathogenesis (postulated):
**Orbital fibroblast is the target cell
- a subpopulation has the ability to **
differentiate into adipocytes
- ↑ TSH receptor expression on orbital fibroblast / adipocytes is a consequence of adipocyte differentiation —> ***Adipogenesis

What stimulates adipogenesis and TSH-R expression in GO orbit
- TRAb level **correlates with clinical score of GO
- **
TRAb stimulate orbital adipocytes (↑ PPARγ, adiponectin, TSH-R gene expression)
- ***TSH also stimulates orbital adipogenesis in GO but not normal orbital preadipocytes (i.e. not in normal individual)

Classification (“NO SPECS”):
- Class 0: No S/S
- Class 1: Only signs, no symptoms (Lid lag, **Lid retraction, Stare)
- Class 2: Soft tissue involvement (signs + symptoms e.g. **
periorbital edema)
- Class 3: **Proptosis
- Class 4: **
EOM involvement
- Class 5: Corneal involvement (
ulceration / scarring)
- Class 6: Sight loss (
optic nerve compression / traction at apex of orbit by enlarged extraocular muscles)

To differentiate GO from other infiltrative eye disease:
- GO: insertion of eye muscle ***spared

Relationship of GO to Thyroid status
- patient may be **hyper / **hypo / **euthyroid
- 80% of patients with GO developed **
eye signs first —> within 18 months of diagnosis of thyrotoxicosis
- Debatable whether ophthalmopathy should affect choice of treatment of hyperthyroidism
- **131-I is associated with higher incidence of ophthalmopathy vs Anti-thyroid drugs (poor control of post-RAI hypothyroidism / high level of TRAb post RAI?)
—> **
Avoid RAI in patients with GO

26
Q

Histology of TED

A

Extraocular muscles:
- **edema
- mononuclear cell infiltration
- **
↑ mucopolysaccharides
- fibrosis

Retrobulbar fat:
- **lymphocyte infiltration
- **
replaced by fibrous tissue
- collagen tissue with hyaluronic acid

Optic nerve:
- atrophy
- ***replaced by fibrous and fatty connective tissue

27
Q

Treatment of GO

A
  1. Rapid control of thyroid dysfunction to euthyroid
    - treatment of hyperthyroidism will ***NOT cure TED —> also need other treatments
  2. **Immunosuppressants for infiltrative ophthalmopathy
    - **
    Steroid (IV / Oral methylprednisolone)
    - ***Cyclosporin A (IV)
    - Plasmapheresis
    - IVIG
    - TNFα inhibitor
  3. ***IGF-1 receptor inhibitor
  4. ***Orbital irradiation
  5. Orbital decompression / Eye muscle operation
    - thinning of **medial wall + **floor (X Lateral wall + Superior roof)
28
Q

Thyrotoxic Periodic Paralysis (TPP)

A
  • mainly in ***Asians, rare in Caucasians
  • predominantly in ***male (25%, female 0.8%)
  • occur in ***ALL causes of thyrotoxicosis (not just Graves’)
  • Skeletal muscles involved

Mechanism:
1. Thyroid hormone —>↑ Na/K-ATPase activity
2. ↑ Adrenergic response —> ↑ Na/K-ATPase activity
3. ↑ **Hypokalaemia
—> ∵ **
enhanced insulin response
—> ↑ Na/K-ATPase activity (esp. after carbohydrate load)
—> insulin drives K into cells
—> shifting from extracellular to intracellular compartment
- Occur ***ONLY during hyperthyroidism but not in euthyroid
- Genetic susceptibility: 17q24.3

Clinical presentation:
1. **Motor involvement mainly (seldom respiratory muscle)
2. Danger of cardiac **
arrhythmia (∵ HypoK + paralysed muscle)
3. **Spontaneous recovery (accelerated by IV K infusion)
4. Attacks prevented by low salt diet, appropriate carbohydrate intake, **
spironolactone, propranolol

Treatment (SpC Revision):
1. IV K infusion
2. Antithyroid drug

29
Q

Hypothyroidism

A

Causes:
1. Autoimmune
- **Atrophic thyroiditis
- **
Hashimoto’s thyroiditis (enlarged Goitre)
2. RAI therapy
3. Subtotal thyroidectomy
4. **Subacute thyroiditis
5. **
Excessive iodide intake (e.g. seaweed) (Wolff–Chaikoff effect)
6. Congenital hypothyroidism
7. ***Iodine deficiency (may contribute transient hypothyroidism at birth)
8. Secondary hypothyroidism (hypothalamic-pituitary disorder)

Clinical patterns (depend on onset):
1. **Cretinism
2. Juvenile myxoedema
3. Adult myxoedema
4. **
Myxoedema coma (most severe form)

30
Q

Signs / Symptoms of Hypothyroidism

A

Symptoms:
Adults:
1. Easy fatiguability
2. Coldness
3. Weight gain
4. **Constipation
5. **
Menstrual irregularities
6. Muscle cramps
7. **Chest pain (∵ **hypercholesterolaemia —> IHD)

Signs:
1. **Dry, coarse skin
2. **
Hoarseness
3. Slow reflex (or failure of relaxation of jerk) (pathognomonic)
4. **Bradycardia
5. **
Pallor

Children:
1. Retardation of growth
2. Mental retardation

Newborn:
1. **Cretinism
2. **
Mental retardation
3. **Short stature
4. Puffy face, flat nose, short neck, thick lips
5. **
Deaf mutism
6. **Protuberant abdomen
7. **
Umbilical hernia
8. ***Jaundice

31
Q

Painless thyroiditis

A

Other names depending on clinical presentation:
1. Lymphocytic thyroiditis
2. Atrophic thyroiditis (atrophic gland)
3. Hashimoto’s thyroiditis (enlarged thyroid with lymphocyte)
4. Post-partum thyroiditis

Variable prognosis depending on residual thyroid reserve

32
Q

Hashimoto’s thyroiditis

A
  • Autoimmune disease
  • common cause of hypothyroidism
  • Low T4, ***High TSH
  • Presence of ***Anti-microsomal (Thyroid peroxidase) Ab
  • Enlarged goitre due to **↑ fibrosis + **infiltration by lymphocytes
  • common in middle-aged females
  • may be associated with ***other autoimmune disease
33
Q

Subacute thyroiditis

A
  • Aka ***De Quervain’s thyroiditis, Giant Cell thyroiditis
  • Preceding ***URTI (e.g. COVID-19)
  • Giant cells + Lymphocyte infiltration of gland
    —> **Granulomatous inflammation
    —> Extravasation of colloid + Follicle destruction
    —> Thyrotoxicosis —> **
    Hypothyroid —> Euthyroid
  • Acute pain, ***tender goitre
  • Fever, **high WBC, **high ESR
  • ***Resolves spontaneously
  • Corticosteroid, NSAID in severe cases
34
Q

Congenital hypothyroidism

A
  • Local incidence 1:3000
  • Neonatal ***cord blood TSH screening
  • Suspicious if at ***2 weeks:
    —> fT4 <12 pmol/L
    —> TSH >7 mIU/L
  • Early treatment —> Preserve brain development

Causes:
1. **Athyreosis
2. **
Dyshormonogenesis
3. Ectopic thyroid gland
4. Associated with other **congenital syndrome (Down’s, Trisomy 18 (Edward’s), Congenital heart disease)
5. **
Hypothalamic-pituitary hypothyroidism
6. **Transient hypothyroidism
- Anti-thyroid drugs in mother with hyperthyroidism
- **
TSH-blocking Ab in mother
- ***Neonatal iodine deficiency
- Premature delivery

Clinical features:
1. **Cretinism
2. **
Mental retardation
3. **Short stature
4. Puffy face, flat nose, short neck, thick lips
5. **
Deaf mutism
6. **Protuberant abdomen
7. **
Umbilical hernia
8. ***Jaundice

35
Q

Incidence of hypothyroidism

A
  • Relates to environmental dietary iodine
  • Higher incidence of autoimmune thyroiditis in iodine-replete countries
  • HK: borderline iodine intake, incidence of autoimmune thyroiditis and hypothyroidism is low (1% vs 10% in Western countries)
36
Q

Hypothyroidism and IHD

A
  • Hyperlipidaemia —> prone to Coronary atherosclerosis
  • Initiation of Thyroxine may ↑ CO —> further worsen IHD
  • ∴ Treat Coronary atherosclerosis ***prior to T4 supplementation
  • Thyroxine takes 4-6 weeks to equilibrate (no need to add thyroxine too quickly)
37
Q

Myxoedematous Coma

A
  • Medical emergency
  • Severe hypothyroidism

Clinical presentation:
1. **Confusion coma
2. **
Hypothermia
3. **Respiratory failure and Hypoxia
4. **
Prone to infection

Treatment:
1. **IV Thyroxine (until cause of hypothyroidism found: Primary vs Secondary)
2. **
IV Hydrocortisone may be necessary (∵ may have concurrent hypoadrenalism + thyroxine may accelerate metabolism of Cortisol in system)

SpC Medicine:
- Thyroid function affect 11-beta-hydroxysteroid dehydrogenase activity —> metabolism of Cortisol

38
Q

(Anti-thyroid AutoAb)

A

(Classification:
1. Anti-TPO Ab (Thyroid peroxidase / Microsomal)
- Hashimoto’s

  1. Anti-Thyroglobulin Ab (ATA)
    - Hashimoto’s
  2. TSH receptor Ab (TRAb) (Stimulating vs Blocking)
    - Graves’)
39
Q

Anti-TPO Ab (SpC Medicine)

A
  1. Diagnosis of AITD (***Autoimmune thyroid disease)
  2. Risk factor of AITD
  3. Risk factor for thyroid dysfunction during Amiodarone therapy
  4. Risk factor for thyroid dysfunction during pregnancy + for post-partum thyroiditis
  5. Risk factor for hypothyroidism during IFN-alpha therapy
40
Q

Anti-Thyroglobulin Ab (SpC Medicine)

A
  • Thyroglobulin (Tg) is polymerised + degraded during process of thyroid hormone synthesis + release

In Non-neoplastic conditions:
- Not usually necessary / cost-effective to order both TPO-Ab and Tg-Ab ∵ TPO-Ab negative patients with detectable Tg-Ab rarely display thyroid dysfunction in iodide sufficient areas

In differentiated thyroid carcinoma:
- Tg-Ab should be measured prior to Tg analysis ∵ low levels of Tg-Ab can interfere with serum Tg measurement

41
Q

TSH receptor AutoAb (TRAb)

A
  • Heterogeneous, types of methods are classified according to their functional activity
  • Lack of correlation between TRAb levels and clinical status largely because of the heterogeneity of Abs
    —> Stimulating / Blocking Ab —> can co-exist within an individual + change over time