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