the thyroid gland

Thyroid physiology

Thyroid gland involved in negative feedback pathway at the level of the hypothalamus and pituitary

What can go wrong and why

Change to any part of the negative feedback loop can lead to thyroid related issues

whole body implication if the thyroid gland produces too little or too much hormones

Causes

• iodine deficiency

• autoimmune disease

• inflammation

• medication or medical treatments

diagnosis

• based on clinical signs and symptoms

• blood levels of T3, T4 and TSH- known as TFTs

• Family history of thyroid conditions

• imaging: thyroid scan, ultrasounds, radioactive iodine uptake test

TFTs

Hypothyrodism

• Low T4 and T3

• High TSH

Hyperthyroidism

• high T4 and or T3

  • Low TSH

goitres

Lumps or swelling at the front of the neck caused by a swollen thyroid gland

• not usually serious

• usually a sign of hypo- hyperthyroidism

associated symptoms

• prolonged cough

• Hoarse voice

• wheezing noice when breathing

• difficulties swallowing

general information

• thyroid diseases respond well to treatment

• even if no symptoms, treatment is recommended to reduce risk of long term complications

• people may feel well even if TSTs deranged

• patient may still have symptoms if TFTs normal/ borderline

  • symptoms usually lag behind treatment changes by several week to months

Factors affecting TFTs

• taking medication for thyroid disorder/ side effect

• non adherence

• Timing of test, especially if immediately after dose

• diurnal variation- normal nocturnal peals may be delayed in night shift workers, insomniacs, vigorous exercise or depression

• condition affecting thyroid- e.g acute illness, adrenal insufficiency obesity

• age

hypothyroidism

clinical disorder where the thyroid gland does not produce sufficient thyroid hormone as per the body requirements

• risk factors

  • female sex

  • family history

  • increasing age

  • diabetes, obesity

  • thyroidectomy

  • certain medication

symptoms

• weight gain

• increased fatigue

• chils

• increased blood pressure and cholesterol

• hair loss

• constipation

• painful and prolonged menstruation

Causes

• iodine deficiency

• autoimmune condition

• congenital hypothyroidism

• other

serious complication if untreated

• Goitre

• cardiovascular problems

• birth defects

• infertility

• mental health disorder

• Myxoedema

• neuromuscular dysfunction and breathing difficulties

• peripheral neuropathy

treatment

• depends on cause

• dietary deficiency - increase iodine in diet

• most commonly due to irreversible changes to thyroid gland requiring life long artificial replacement of thyroid hormones

  • classed as a chronic condition

  • cannot be managed with non pharmacological advice

• treatment: levothyroxine ( artificial T4 replacement )

Levothyroxine

dose= adjusted according to response

starting dose- 1.6mcg/kg

take 30- 60 mins before breakfast, caffeine and other meds

monitoring every 3 months until stable, then yearly

hypothyroidism of pregnancy

• women with hypothyroidism can have difficulties conceiving

• need to have specialist input during pregnancy itself

• will likely need higher doses of levothyroxine during pregnancy, especially during first 20 weeks to provide sufficient supply to baby

• will likely return to pre pregnancy dose after baby is born

• may develop post party thyroiditis- initially signs of hyperthyroidism, then usually resolves itself or will further develop signs of hypothyroidis

• safe to breast feed

myxoedema coma

rare life threatening complication of hypothyroidism

• causes: prolonged low thyroxine levels or poorly controlled hypothyroidism

• symptoms: bradycarida, hypotension, hypothermia, oedema, and confusion due to organs shutting down

• manament- classed as medical emergency

Hyperthyroidism

clinical disorder where the thyroid gland produces too much thyroid hormones as per body requirements

risk factors

= female sex

• family history

• recent pregnancy

• smoking

• PMHx- diabetes, autoimmune disease

symptoms

• dryness, corneal erosions

• irritability anxiety, depression insomnia

• sweating early grey

• infertility, merger menstruation, decreased potency

• hypotrophy of muscles tremors in the body

• increased appetite indigestion, diarrhoea, abdominal pain

• thirst copious urination

• heart rhythm

causes

• Graves disease

• TSH receptor antibodies stimulate TSH receptor= thyroid hyperplasia and excessive hormone production

• thyroidal origin

• other

serious complication if untreated

• goitre

• graves orbitopathy

• thyrotoxic crisis

• cardiovascular

• osteoporosis

• muscle paralysis

Treatment

• need to refer to endocrinologist

• start beta blocker

• aim of beta blocker: provider relief from adrenergic symptoms

• specialist will decide on best approach

• 1st choice: thyroid ablation

• second choice- conservative management with antithyroid drugs

Thyroid ablation

• thyroidectomy

  • radioiodine

thyroidectomy

• surgical procedure to remove part or while thyroid gland

  • must take care not to damage parathyroid glands

radioiodine

• radioactive iodine is administered orally or intravenously induces damage of DNA= death of thyroid cells reduces function and/ or thyroid gland

treatment with antithyroid drugs

• decrease thyroid hormone synthesis

regimens post euthyrodism

• titration- block regime

• dose of antithyroid drug adjusted regularly based on TFTs

• start with high dose of antithyroid drug to block thyroxine production

• gradually reduced the dose to the lowest dose needed to maintain a euthyroid state

carbimazole

• must tell doctor immediately if develop sore throat, mouth ulcers

• avoid in pregnancy

Propythiouracil

must tell doctor immediately if develop anorexia, nausea, vomiting, fatigue

preferred for pregnancy

Hyperthyroidism and pregnancy

• women with hyperthyroidsm can have difficulties conceiving

• need to have specialist input during pregnancy itself and ideally pre conception to ensure on safe med

  • will likely need lower doses of propylthiocil in graves disease

thyrotoxic crisis

causes- undiagnosed hyperthyroidism/ abruptly stopping antithyroid drugs

symptoms - fever, jaundice, tachycardia

management- classed as medical emergency. aggressive treamtne with antithyroid drugs, beta blockers, lugs iodine