Hypothyroidism Flashcards
What is hypothyroidism?
Hypothyroidism is a common endocrine condition caused by a deficiency in thyroid hormone.
Reduction in circulating T3 and T4
What are the classification for hypothyroidism?
Primary - 95% of cases
Secondary
Congenital
Epidemiology
- Hypothyroidism 1-2% in world
- Hashimoto’s thyroiditis being the most common cause in the developed world. Iodine deficiency is the most common cause worldwide.
- Female gender: 5-8x more likely to develop than men
- Middle-aged: peak age is 30-50 years old in Hashimoto’s thyroiditis
Hashimotos thyroiditis
- Autoimmune process associated withHLA-DR5andanti-TPO antibodies,which act as competitive inhibitors for the enzyme
- Associated with other autoimmune conditions e.g. type 1 diabetes and Addisons disease
- Diffuse painless goitre and can experience a transient thyrotoxic state known as hashitoxicosis
- 5-10x more common in women
- Increased risk of Non-Hodgkin lymphoma
De Quervain’s thyroiditis
- Follows a viral prodrome and can also present with a transient thyrotoxic state
- Painfulgoitre withraised inflammatory markers. Usually self-limiting
Post partum thyroiditis
- Autoimmune with most patients developingthyrotoxicosiswithin the first 6 months of birth, with subsequenthypothyroidism
- Most patients’ thyroid function normalises by 12 months
Riedels thyroiditis
- Hard non-tender thyroid goitre due to fibrous tissue
- Causes a painless goitre
Iodine deficiency
- Commonest causeworldwide, due to dietary deficiency
- Uncommon in the developed world due to iodine-fortified salt and foods
Post- thyroidectomy or post radioiodine
After treatment for hyperthyroidism e.g. Graves’ disease, patients can experience long term hypothyroidism and require levothyroxine replacement
Drugs that cause primary hypothyroidism
- Amiodarone - can cause both hyperthyroidism (due to the high iodine content of amiodarone) and hypothyroidism (since it also inhibits the conversion of T4 to T3)
- Lithium
- Anti-thyroid drugs e.g. carbimazole
Secondary causes of hypothyroidism
- Often due to compression from apituitarytumour(e.g. adenoma), but may occur following surgery/radiation or vascular pathology (e.g. pituitary apoplexy)
- Rarely, it may be due tohypothalamicpathology, e.g. a tumour
- Drugs: cocaine, steroids and dopamine all inhibit TSH secretion
What is primary hypothyroidism?
due to pathology affecting the thyroid gland itself, such as an autoimmune disorder (e.g. Hashimoto’s thyroiditis) or iodine deficiency.
What is Secondary hypothyroidism?
usually due to pathology affecting thepituitarygland (e.g. pituitary apoplexy) or a tumour compressing the pituitary gland. It may also be caused byhypothalamicdisorders and certain drugs.
What is congenital hypothyroidism?
occurs due to an absent or poorly developed thyroid gland (dysgenesis), or one that has properly developed but cannot produce thyroid hormone (dyshormonogenesis).
RFs for hypothyroidism
- Family history
- History of autoimmunity
- Genetic disorders: Turner and Down syndrome
- Chest or neck irradiation
- Thyroidectomy or radioiodine
Signs of hypothyroidism
- Dermatological: hair loss, loss of lateral aspect of the eyebrows (Queen Anne’s sign), dry and cold skin, coarse hair
- Bradycardia
- Goitre
- Decreased deep tendon reflexes
- Carpal tunnel syndrome
- Hoarse voice
Symptoms of hypothyroidism
Weight gain
Fluid retention
Dry skin
Constipation
Lethargy
First line investigations for hypothyroidism
TFTs:
Hashimoto’s (primary hypothyroidism) TSH High T3/T4 Low
Subclinical hypothyroidism High TSH Normal T4
Secondary hypothyroidism Low/ normal TSH Low T4
Other investigations to do for hypothyroidism
Antibodies:Anti-TPO is associated with Hashimoto’s thyroiditis in 95% of cases
Inflammatory markers:raised in de Quervain’s thyroiditis
Can also do for hypothyroidism investigations
US
Fasting lipids
Serum glucose + HbA1c
FBC
1st line therapy for hypothyroidism
Levothyroxine (T4):offer 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
Aim to maintain serum TSH and T4 levels at normal range
What must all patients with secondary hypothyroidism require?
urgent referral to an endocrinologist.
Pregnancy and postpartum hypothyroidism
- If TFTs are abnormal, advise delaying conception and using contraception until stabilised on levothyroxine
- Inform the woman that there is anincreased demand for levothyroxinein pregnancy, with the dose usually increased by at least 25-50 mcg and aiming for a low-normal TSH
Complications of hypothyroidism
CVD - hypercholesterolaemia is associated with ischaemic heart disease
Neuro - Carpal tunnel, peripheral neuropathy
Myxoedema coma
Thyroid lymphoma
Thyroxine side effects
- Hyperthyroidism
- Atrial fibrillation
- Osteoporosis
- Angina
What is Hashimotos Thyroiditis?
The most common cause of hypothyroidism in the West. Antithyroid antibodies is the cause for this type of hypothyroidism
Epidemiology of Hashimotos Thyroiditis
- It is estimated to affect between 0.5% and 2% of the population.
- More common in FEMALES than males
- Incidence increases with age
RFs for Hashimotos Thyroiditis
- Female sex
- Associated with other autoimmune disease e.g. T1DM
- Associations with Turner’s and Down’s syndrome
