Hypothyroidism Flashcards
Hypothyroidism
Thyroid hormone (thyroxine [T4] + tri-iodothyronine [T3]) deficiency
What are the subtypes of hypothyroidism?
Primary: Overt + Subclinical
Secondary (central)
What is primary hypothyroidism?
Thyroid hormone deficiency due to thyroid gland being unable to produce thyroid hormones because of iodine deficiency or an abnormality within the gland itself
What is subclinical hypothyroidism?
TSH: high
T3+T4: normal
What is secondary hypothyroidism?
Thyroid hormone deficiency as a result of insufficient thyroid stimulation due to a pituitary or hypothalamic disorder
5 causes of primary hypothyroidism
AI thyroiditis (most common in UK)
Iodine deficiency (most common cause worldwide)
Post-ablative therapy/ surgery
Drug therapy
Subacute (de Quervain’s)
What is Hashimoto’s thyroiditis?
AI thyroiditis a/w goitre
Describe the epidemiology of hypothyroidism
1-2% F in UK
F > M
List 3 drugs that can cause hypothyroidism
Lithium
Amiodarone
Anti-thyroid drugs e.g. Carbimazole
What occurs subacute thyroiditis/ postpartum thyroiditis?
Transient thyroiditis
Initial brief hyperthyroidism followed by longer period hypothyroidism
List 3 conditions associated with Hashimoto’s thyroiditis
T1DM
Addisons
Pernicious anaemia
List 8 S/S of hypothyroidism
Weight gain
Lethargy
Cold intolerance
Constipation
Menstrual irregularities/ sub fertility
Carpal tunnel syndrome
Dry skin
Hair loss
Investigations for hypothyroidism
FBC: a/w pernicious anaemia
TFTs
HbA1c: a/w T1DM
Coeliac serology
Serum lipids
Thyroid antibody testing
Describe TFTs in hypothyroidism
High TSH
Low T3 + T4
What antibodies may be detected in hypothyroidism?
Thyroid peroxidase antibodies (TPOAb)
TSH receptor antibodies (TRAbs)
What drug is used in treatment of hypothyroidism? How should it be taken?
Levothyroxine sodium
Take on empty stomach in morning before food
Describe the clinical effects of levothyroxine
Sx may lag behind Tx changes for several weeks or months
Describe monitoring in hypothyroidism
Recheck TSH every 3 months after initiation
Adjust dose according to Sx + TFTs
Once 2 similar measurements 3 months apart, check annually
What is the starting dose of levothyroxine?
50-100 micrograms OD
If cardiac disease, severe hypothyroidism or >50: initial starting dose should be 25mcg OD with dose slowly titrated
How does levothyroxine dosing change during pregnancy?
Increase dose by at least 25-50 micrograms
(increased demands during pregnancy)
List 4 side effects of levothyroxine therapy
Hyperthyroidism: due to over Tx
Reduced bone mineral density
Worsening of angina
Atrial fibrillation
Which drugs cause reduced absorption of Levothyroxine?
Iron
Calcium carbonate
List 7 complications of untreated hypothyroidism
Dyslipidaemia
Metabolic syndrome
Coronary heart disease
Stroke
Heart failure
Infertility
Decreased taste, vision + hearing
What is a life-threatening complication of hypothyroidism? How may this present?
Myxoedema coma
Presents with
Lethargy
Bradycardia
Hypothermia
Seizures
Coma
What may precipitate myxoedema coma?
Heart failure
Sepsis
Stroke
