Hypothyroidism Flashcards
Definition
The clinical syndrome resulting from insufficiency secretion of thyroid hormones
Aetiology/Risk factors (primary)
· 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
Aetiology/Risk factors (secondary)
· SECONDARY HYPOTHYROIDISM (5% of cases)
o Pituitary and Hypothalamic Disease - resulting in reduced TSH and TRH and, hence, reduced stimulation of thyroid hormone production
Epidemiology
· 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)
Presenting symptoms
· 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)
Presenting symptoms (myxoedema coma)
· Myxoedema coma (severe hypothyroidism usually seen in the elderly):
o Hypothermia o Hypoventilation o Hyponatraemia o Heart failure o Confusion o Coma
Signs on physical examination
· 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
Investigations
· Bloods
o TFTs
o FBC - may show normocytic anaemia
o U&Es - may show low sodium
o Cholesterol - may be high
Management plan (chronic)
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
Management plan (myxoedema coma)
o Oxygen o Rewarming o Rehydration o IV T4/T3 o IV hydrocortisone o Treat underlying cause (e.g. infection)
Possible complications
· Myxoedema coma
· Myxoedema madness (psychosis with delusions and hallucinations or dementia)
Prognosis
· Lifelong levothyroxine is required
· Myxoedema coma mortality = 80%