Hypothyroidism Flashcards
Causes of primary hypothyroidism
- Thyroiditis
- Hashimoto’s thyroiditis (commonest cause in developed world)
- De Quervain’s thyroiditis
- Post-partum thyroiditis
- Iodine deficiency (most common cause worldwide)
- Post thyroidectomy or post radioiodine
- Drugs
- Amiodarone
- Lithium
- Anti thyroid drugs
- Subclinical hypothyroidism
Hashimoto’s thyroiditis
1) Specific features
2) Associated with which gene?
3) Associated with which antibodies?
4) Associated with which conditions?
5) Increased risk of which disease?
- Diffuse painless goitre and can experience a transient thyrotoxic state known as hashitoxicosis.
- HLA-DR5
- Anti-TPO antibodies, which act as competitive inhibitors for the enzyme
- Associated with other autoimmune conditions e.g. type 1 diabetes mellitus and Addison’s disease
- Increased risk of Non-Hodgkin lymphoma (usually diffuse large B cell lymphoma)
De Quervain’s thyroiditis
Specific features
Follows a viral prodrome and can present with a transient thyrotoxic state.
Painful goitre with raised inflammatory markers. Usually self-limiting.
Post partum thyroiditis
Autoimmune with most patients developing thyrotoxicosis within the first 6 months of birth, with subsequent hypothyroidism
Most patients’ thyroid function normalises by 12 months
Risk factors for hypothyroidism
- Female gender: 5-8x more likely to develop than men
- Middle-aged: peak age is 30-50 years old in Hashimoto’s thyroiditis
- Family history
- History of autoimmunity: e.g. pernicious anaemia, T1DM, coeliac disease
- Genetic disorders: Turner and Down syndrome
- Chest or neck irradiation
- Thyroidectomy or radioiodine
Symptoms of hypothyroidism
- Weight gain
- Cold intolerance
- Lethargy
- Dry skin
- Constipation
- Menorrhhagia: followed later by oligomenorrhoea and amenorrhoea
Signs of hypothyroidism
- Dermatological: hair loss, loss of lateral aspect of the eyebrows, dry and cold skin, coarse hair
- Bradycardia
- Goitre
- Decreased deep tendon reflexes
- Carpal tunnel syndrome
- Hoarse voice: unusual
Investigations for hypothyroidism
- TFTs
- Antibodies
- Inflamatory markers: raised in de Quervain’s thyroiditis
Interpretation of the following TFTs
TSH high, T4 low
TSH high, T4 normal
TSH low or normal, T4 low
- TSH high, T4 low: Primary hypothyroidism
- TSH high, T4 normal: Subclinical hypothyroidism
- TSH low or normal, T4 low: Secondary hypothyroidism eg non-secretory pituitary adenoma
Autoantibodies present in Hashimoto’s thyroiditis
- Anti-TPO 90-95%
- Anti-thyroglobulin 30-50%
- Anti-TSH receptor 0-5%
Aims of treatment of hypothyroidism
To resolve signs and symptoms and to maintain serum TSH and T4 levels within or close to the normal reference range (0.5-2.5 mU/L).
Management of overt hypothyroidism
-
Levothyroxin (T4) with regular review of symptoms and TSH every 3 months. Once TSH is stable (on 2 occasions at least 6 months apart), review TSH annually
- T4 starting dose: 50-100mcg once daily for most patients
- Lower starting dose: 25mcg once daily titrated slowly if >50 years, severe hypothyroidism or a history of iscahemic heart disease
- Review after 8-12 weeks when dose changed
Levothyroxin drug interaction
Iron and calcium carbonate reduce levothyroxin absorption so should be given ≥ 4 hour apart
Management of subclinical hypothyroidism
- TSH > 10mU/L and normal T4 (on two occasions): consider levothyroxin
- TSH < 10mU/L and normal T4 (on two occasions): consider a 6 month trial of levothyroxin if symptomatic and less than 65 years old
How dose pregnancy affect the management of hypothyroidism?
There is an increased demand for levothyroxine in pregnancy, with the dose usually increased by at least 25-50 mcg and aiming for a low-normal TSH.
