Hypothyroidism

Question 1

Definition

Answer 1

The clinical syndrome resulting from insufficiency secretion of thyroid hormones

Question 2

Aetiology/Risk factors (primary)

Answer 2

· PRIMARY HYPOTHYROIDISM (decreased thyroid hormone production)

o Acquired
· Hashimoto's thyroiditis (autoimmune)
· Iatrogenic (post-surgery, radioiodine, hyperthyroid medication)
· Severe iodine deficiency
· Iodine excess (Wolff-Chaikoff effect)
· Thyroiditis

o Congenital
· Thyroid dysgenesis
· Inherited defects in thyroid hormone biosynthesis

Question 3

Aetiology/Risk factors (secondary)

Answer 3

· SECONDARY HYPOTHYROIDISM (5% of cases)

o Pituitary and Hypothalamic Disease - resulting in reduced TSH and TRH and, hence, reduced stimulation of thyroid hormone production

Question 4

Epidemiology

Answer 4

· 0.1-2% of adults
· 6 x more common in FEMALES
· Most common age of onset > 40 yrs
· Iodine deficiency is seen in mountainous areas (e.g. Himalayas)

Question 5

Presenting symptoms

Answer 5

· INSIDIOUS onset
· Cold intolerance
· Lethargy
· Weight gain
· Reduced appetite
· Constipation
· Dry skin
· Hair loss
· Hoarse voice
· Mental slowness
· Depression
· Cramps
· Ataxia
· Paraesthesia
· Menstrual disturbance (irregular cycles, menorrhagia)
· History of surgery or radioiodine therapy for hyperthyroidism
· Personal/family history of other autoimmune conditions (e.g. Addison's, type 1 diabetes mellitus)

Question 6

Presenting symptoms (myxoedema coma)

Answer 6

· Myxoedema coma (severe hypothyroidism usually seen in the elderly):

o Hypothermia
o Hypoventilation
o Hyponatraemia
o Heart failure
o Confusion
o Coma

Question 7

Signs on physical examination

Answer 7

· Hands
o Bradycardia
o Cold hands

· Head/Neck/Skin
o Pale puffy face
o Goitre
o Oedema
o Hair loss
o Dry skin
o Vitiligo

· Chest
o Pericardial effusion
o Pleural effusion

· Abdomen
o Ascites

· Neurological
o Slow relaxation of reflexes
o Signs of carpal tunnel syndrome

Question 8

Investigations

Answer 8

· Bloods

o TFTs
o FBC - may show normocytic anaemia
o U&Es - may show low sodium
o Cholesterol - may be high

Question 9

Management plan (chronic)

Answer 9

o Levothyroxine (25-200 mcg/day)

· IMPORTANT: rule out underlying adrenal insufficiency before starting thyroid hormone replacement

· Thyroid hormone replacement in the context of adrenal insufficiency can precipitate an Addisonian crisis

· Adjust dose based on clinical picture and TFTs

Question 10

Management plan (myxoedema coma)

Answer 10

o Oxygen
o Rewarming
o Rehydration
o IV T4/T3
o IV hydrocortisone
o Treat underlying cause (e.g. infection)

Question 11

Possible complications

Answer 11

· Myxoedema coma

· Myxoedema madness (psychosis with delusions and hallucinations or dementia)

Question 12

Prognosis

Answer 12

· Lifelong levothyroxine is required

· Myxoedema coma mortality = 80%