Hypothyroidism

Hypothyroidism

Hypothyroidism is a deficiency of the thyroid hormones T3 and T4. The presentation of thyroid disease can be subtle and non-specific since almost all cell nuclei have thyroid receptors which affect various metabolic processes. Prognosis is good if treated but can be disastrous if left untreated.

Hypothyroidism is common, affectine 4 per 1000 individuals per yeat.

Classification of Hypothyroidism

Classification	Description	Causes	Lab findings
Primary hypothyroidism	Decreased production of thyroid hormon from the thyroid gland	Hashimoto thyroiditis, drug-induced hypothyroidism, thyroiditis, iatrogenic (post RAI ablation), iodine deficiency, congenital (dysplasia or aplasia)	High TSH, low T3 and T4
Primary hypothyroidism	Primary autoimmune	Primary atrophic hypothyroidism (due to diffuse lymphocytic infiltration), Hashimoto’s thyroiditis
	Drug-induced	Antithyroid drugs, amiodarone, lithium, iodine
	Iatrogenic	Post-thyroidectomy, post-radioiodine ablation
	Subacute thyroiditis	Temporary hypothyroidism after hypothyroid state
	Iodine deficiency	Most common cause worldwide
Secondary hypothyroidism	Decreased thyroid hormone due to decreased TSH (hypopituitarism). Very rare	Tumor, mass effect	Low TSH, low T3 and T4
Tertiary hypothyroidism	Decreased thyroid hormone due to decreased TRH. Very rare	Tumor, mass effect	Low TSH, low T3 and T4

Signs and symptoms of hypothyroidism

Classification	Signs and symptoms
Reduced metabolic rate	Fatigue, cold intolerance, weight gain despite reduced appetite, constipation, bradycardia, decreased deep tendon reflexes, hair loss
Increased stimulation	Painless goitre
Increased TRH	Hyperprolactinaemia, menorrhagia, amenorrhoea, galactorrhoea
Deposition of glycosaminoglycans	Myxoedema (non-pitting oedema), hoarsenesss, pretibial and periorbital oedema
Psychiatric	Depression, psuedodementia (older individuals), impaired memory or cognition

• Associated conditions
  • Type 1 diabetes mellitus
  • Addison’s disease
  • Turner’s and Down’s syndrome
  • Cystic fibrosis
  • Primary biliary cholangitis
  • Ovarian hyperstimulation
  • POEMS syndrome (Polyneuropathy, organomegaly, endocrinpathy, M-protein band)
  • Dyshormonogenesis e.g. Pendred’s syndrome
• Signs and symptoms
  • Fatigue (most common complaint)
  • Cold intolerance
  • Weight gain
  • Reduced appetite
  • Constipation
  • Hair loss
  • Painless goitre
  • Menstrual cycle abnormalities
  • Pretibial and periorbital oedema
  • Depression
  • Pseudodementia
  • Reduced memory
• Physical examination (BRADYCARDIC)
  • Bradycardia
  • Reflexes reduced
  • Ataxia (cerebellar)
  • Dry-thin hair or skin
  • Yawning, drowsy or coma
  • Cold peripheries due to reduced temperature
  • Ascites +/- non-pitting oedema +/- pericarial or pleural effusion
  • Round puffy face or obsese
  • Defeated demeanour
  • Immobile +/- Ileus
  • Congestive heart failure
• Investigations
  • Complete blood count: rule out anaemia as a cause of fatigue
    • Normocytic anaemia may be present in hypothyroidism
    • Microcytic anaemia may be present in women with hypothyroidism
  • Basic metabolic panel: rule out
  • Thyroid funciton tests
• Treatment
  • Daily Levothyroxine (T4)
    • Start at a lower dose in elderly patients or those with ischaemic heart disease (may precipitate angina or MI) e.g. 25 mcg
    • Other patients can be started at 50 – 100 mcg
    • Review at 12 weeks
    • Adjust 6-weekly by clinical state and normalize TSH (0.5 – 2.5 mU/L)
    • Increase dose by 25 – 50 ug in pregnant women and monitor TSH (while aiming for lower values)
• Side-effects of levothyroxine
  • Hyperthyroidism (over treatment)
  • Reduced bone mineral density
  • Worsenign of angina
  • Atrial fibrilation
  Levothyroxine also interacts with iron absorption and should be given at least 2 hours apart
• Complications of hypothyroidism
  • Hypercholesterolemia
  • Myxedema coma
• Complications of hypothyroidism in pregnancy
  • Eclampsia
  • Anaemia
  • Prematurity
  • Low birthweight
  • Stillbirth
  • Post-partum hemorrhage