Hypothyroidism

 

• Background

  Causes

  Autoimmune:

  • Hashimoto's thyroiditis (aka autoimmune thyroiditis, chronic lymphocytic thyroiditis): commonest cause.
  • Primary atrophic hypothyroidism.
  • Hypopituitarism leading to secondary ↓TH (5% of cases).

  Iodine:

  • ↓Iodine
  • ↑↑Iodine: floods sodium-iodine symporter, eventually causing downregulation.
  • Radioiodine

  Iatrogenic:

  • Lithium
  • Surgery

  Congenital agenesis.

  Epidemiology

  Prevalence >60 years old: 6% of women, 2% of men.

• Signs and symptoms

  Symptoms

  • Systemic: fatigue, cold, ↑weight.
  • Dermatological: dry skin, itch, brittle hair, hair loss, coarse features, oedema.
  • Constipation
  • Menorrhagia
  • Weakness, proximal or global.
  • ↓Memory/cognition

  Compression by goitre can lead to:

  • Dysphagia
  • SOB ± stridor.
  • Hoarseness

  Signs

  Neck:

  • Hashimoto's: initially firm, non-tender, goitre, but later fibrotic and shrunken.
  • Iodine deficiency: goitre.
  • Most other causes: no goitre.

  BRADYCARDIC:

  • Bradycardia
  • Reflexes relax slowly.
  • Ataxia (cerebellar)
  • Dry thin hair/skin.
  • Yawning/ drowsy.
  • Cold hands
  • Ascites, non-pitting oedema, pericardial/pleural effusion.
  • Round puffy face.
  • Defeated demeanour.
  • Immobile bowel, Ileus.
  • CHF, Carpal tunnel syndrome.

• Investigations

  Thyroid:

  • Screen with TSH (↑) and confirm with T4 (↓). In secondary (pituitary) hyperthyroidism, both ↓; measure both from the start if this is suspected or patient is young. No need to check T3.
  • ↑TPO-Ab in autoimmune thyroid disease. Should be checked in subclinical hypothyroidism as its presence is an indication for more frequent monitoring, but otherwise not routinely indicated as does not affect management.
  • TSHR-Ab only needs checking in thyroid eye disease.

  Others:

  • Hb: ↓Fe anaemia due to menorrhagia. Macrocytic anaemia is possible but rare.
  • Lipids: ↑cholesterol, ↑TG.
  • ↑CK in severe disease, due to myopathy.

• Management

  • Levothyroxine (T4).
  • No evidence of benefits from T3.
  • Check TSH annually once stable.
  • Increase T4 dose during pregnancy.

• Levothyroxine (T4)

  Management

  • Onset takes several weeks.
  • Titrate up every 2-3 months until TSH in range and stable.
  • Take on empty stomach, at least 30 minutes before breakfast, caffeine, or other drugs, which all may interfere with absorption.

  Cautions

  MI risk in elderly and those with IHD, so start at low dose and build up.

• Complications

  Myxoedema coma.

  Chronic:

  • Heart disease.
  • Dementia

  In pregnancy:

  • Eclampsia
  • Anaemia
  • Prematurity
  • Small for gestational age baby.

• Myxoedema coma

  Pathophysiology

  • Severe, acute manifestation of hypothyroidism with 50% mortality.
  • Often follows an illness (infection, stroke, seizure, surgery) or medication (sedatives).

  Signs and symptoms

  • Hypothermia
  • Neuro: ↓reflexes, seizures, coma.
  • ↓Glucose
  • ↓HR.

  Management

  • T3 IV.
  • Give corticosteroids first as Addison's may be present, either as an alternative diagnosis or co-morbid in hypopituitarism.