Hypothyroidism Flashcards
Define hypothyroidism
Syndrome resulting from insufficient secretion of thyroid hormones (T4 and T3)
What are the causes of congenital hypothyroidism
Thyroid agenesis (most common cause of sporadic congenital hypothyroidism): missing, ectopic or poorly developed thyroid e.g. DiGeorge syndrome
Maldescent of the thyroid - thyroid remains as a lingual mass or a unilobular small gland
Dyshormonogenesis - inborn error or thyroid hormone synthesis, autosomal recessive
Maternal iodine deficiency
TSH deficiency (Secondary): tumours, ischaemic damage
Transient hypothyroidism e.g. carbimazole, maternal Abs (Hashimoto’s)
What are the causes of acquired hypothyroidism
Primary (95%): failure to produce hormones
- Autoimmune (Hashimoto’s) thyroiditis
- Iatrogenic (post-surgery, radioiodine, hyperthyroidism treatment)
- Severe iodine deficiency or iodine excess (Wolff-Chaikoff effect)
- Thyroiditis e.g. De Quervain’s
- Drugs e.g. lithium, amiodarone, aminoglutethimide, interferon alpha, thalidomide, tyrosine kinase inhibitors
Secondary (5%): underproduction of TSH
- pituitary/hypothalamic disorder e.g. pituitary adenoma, surgery, radiation
What are the risk factors for hypothyroidism
Female
Down’s syndrome
Turner’s syndrome
Autoimmune disorders e.g. vitiligo, rheumatoid arthritis, diabetes mellitus
Polyglandular autoimmune syndrome type II (Addison’s + hypothyroidism)
Iodine deficiency (maternal)
What are the symptoms and signs of acquired hypothyroidism
Obesity or Weight gain with reduced appetite
Short stature or FTT
Delayed puberty/amenorrhoea
Cold intolerance
Constipation
Poor concentration, Deterioration in school work, Learning difficulties
Weakness or myalgia
Lethargy, depression
Goitre
Thin, dry hair and skin
Oedema and loss of eyebrows
Bradycardia
Slow-relaxing reflexes
SUFE
What are the symptoms and signs of congenital hypothyroidism
Usually asymptomatic and picked up on screening
Prolonged jaundice
Faltering growth
Reduced feeding
Constipation
Pale, cold, mottled dry skin
Coarse facies
Large tongue
Hoarse cry
Goitre
Umbilical hernia
Delayed development
What are the differentials for hypothyroidism
Sick euthyroid syndrome
T1Dm
Addison’s disease
Coeliac disease
Atrophic gastritis
Anaemia
Multiple myeloma
CKD
What are the features of myoxoedema coma
Hypothermia
Hypoventilation
Hyponatraemia
HF
Confusion
Coma
What investigations should be done for hypothyroidism
Bloods:
- TFTs: TSH↑ primary | TSH↓ secondary | T4 depressed
- TPO antibodies: ↑ Hashimoto’s
- FBC: mild, normocytic anaemia
- U&Es: ? myxoedema coma
- Cholesterol
- Glucose: ?T1DM
Other:
- US neck: thyroid may be absent, ectopic, abnormal in size and shape, normal
- X-ray bones: bone age delayed
- Pituitary function and visual field testing: differentiate between primary and secondary
What does the TSH result suggest after testing for congenital hypothyroidism
<8 = Negative for CHT
8-20 = Borderline for CHT → re-test 7-10 days after the initial sample → >8 = suspected CHT
> 20 = Suspected CHT → refer to a paediatrician
What is the management for hypothyroidism
Levothyroxine sodium oral 25-200 micrograms/day
Congenital: start within 2-3 weeks of age to reduce neurodevelopment impairment
Use TSH to guide dose (aim to suppress TSH) (if secondary, use fT4 to guide dose)
Monitor: 2w, 4w, 8w, 3m, 4m, 6m, 8m, 10m, 12m, every 2-3 months at 1yo, every 3-4m at 2yo, every 6-12 weeks until TSH is stabilise, every 4-6m until puberty, once a year post-puberty
What is the management for myxoedema coma
- Oxygen
- Rewarming
- Rehydration
- IV T4/T3 liothyronine sodium then levothyroxine
- IV hydrocortisone
What are the complications of hypothyroidism
Myxoedema coma
Myxoedema madness (psychosis)
Growth failure
Osteoporosis
Metabolic syndrome
Resistant hypothyroidism
Neurological and cognitive: reduced taste, vision, hearing, impaired attention, concentration, memory, language
Sick sinus: sinus node dysfunction with inappropriate atrial rate
Cardio: angina, AF, CHD, stroke, HF
What is the prognosis for hypothyroidism
Lifelong therapy required
Generally excellent prognosis with full recovery if treated
Myxoedema coma has mortality of up to 80%
With adequate and early intervention, intelligence and development should be normal
