Hypothyroidism
Prevalence
Between 0.1 and 2% of the population
Subclinical is 4 to 10% of adults
5 to 8 times more likely in women
More common in women with small body size at birth and during childhood
NHANES study showed
Hypothyroid in 4.6%
Hyperthyroid in 1.3%
Anti-TPO positive in 11%
Clinical
Slowing of metabolic process
Cold intolerence
Fatigue and weakness
Weight gain
Cognitive dysfunction
Intellectual disability if infantile onset
Constipation
Growth failure
Slow movement and speech
Delayed relaxation of tendon reflexes
Bradycardia
Carotenemia
Accumulation of matrix substances
Dry skin
Hoarseness
Oedema
Coarse skin
Puffy faces and loss of eyebrows
Periorbital oedema
Enlargement of the tongue
Other
Decreased hearing
MYalgia and paraesthesia
Depression
Menorrhagia
Arthralgia
Pubertal delay
Diastolic hypertension
Pleural and pericardial effusions
Ascites
Galactorrhoea
Diagnosis
Primary Hypothyroidism - High TSH and low serum T4
Central Hypothyroidism - Low serum T4 and TSH that is not appropriately elevated
Differential
Low TSH
Primary hyperthyroidism
Incomplete recovery from hyperthyroidism
Nonthyroidal illness
High levels of chorionic gonadotropin (early pregnancy)
Drugs
Central hypothyroidism
High TSH
Primary hypothyroidism
Recovery from nonthyroidal illness
Drugs
TSH producing tumours
Adrenal insufficiency
Generalised thyroid hormone resistance
Primary Hypothyroidism
Chronic autoimmune thyroiditis
Iatrogenic
Thyroidectomy
Radioiodine therapy or external irradiation
Iodine deficiency or excess
Drugs - thionamides, lithium, amiodarone, interferon alfa, interleukin-2, tyrosine kinase inhibitors, checkpoint inhibitor immunotherapy
Infiltrative diseases - fibrous thyroiditis, hemochromatosis, sarcoidosis
Transient hypothyroidism
Painless (silent, lymphocytic) thyroiditis
Subacute granulomatous thyroiditis
Postpartum thyroiditis
Subtotal thyroidectomy
Following radioiodine therapy for Graves' hyperthyroidism
Following withdrawal of suppressive doses of thyroid hormone in euthyroid patients
Congenital thyroid agenesis, dysgenesis, or defects in hormone synthesis
Hashimoto’s
Goitrous autoimmune thyroiditis
Atrophic autoimmune thyroiditis
Goals of treatment
Amelioration of symptoms
Normalization of serum TSH secretion
Reduction in the size of goitre (if present)
Avoidance of overtreatment (iatrogenic thyrotoxicosis)
Treatment
Aim to keep TSH in the normal range 0.5 to 4
The argument can be made that the upper limit should be 2.5
Levothyroxine
The average full dose is 1.6mcg/kg of body weight
Range varies from 50mcg to 200mcg
Can start at 1.6mcg in young people but in older patients start slow at 25 to 50mcg
Empty stomach with water ideally 30 to 60 minutes before food
Symptoms improve in 2 weeks but complete recovery takes months
Steady-state concentration not achieved until 6 weeks