Hypothyroidism Flashcards
what is the definition of hypothyroidism?
Underactivity of the thyroid gland may be primary, from disease of the thyroid gland, or much less commonly, secondary to hypothalamic or pituitary disease (secondary hypothyroidism)
what is the epidemiology of hypothyroidism?
- Worldwide the chief cause of primary hypothyroidism is iodine deficiency
- The most common cause of primary hypothyroidism in areas with no iodine deficiency is autoimmune/atrophic hypothyroidism
- Affects 0.1-2% of the population
- More common in FEMALES than males
- Incidence increases with age
- Autoimmune hypothyroidism is associated with other autoimmune disease
e. g. DMT1, Addisons’, pernicious anaemia - In general hypothyroidism is associated with Turner’s (only affects females, only have one X chromosome as opposed to the normal XX) & Down’s (trisomy 21) syndrome, cystic fibrosis, primary biliary cirrhosis and ovarian hyper-stimulation
what is the aetiology of hypothyroidism?
- AUTOIMMUNE/ATROPHIC HYPOTHYROIDISM:
• The most common cause of hypothyroidism
• Associated with antithyroid autoantibodies leading to lymphoid infiltration of the gland and eventual atrophy and fibrosis - since there is atrophy there is NO GOITRE
• More common in FEMALES than males
• Incidence increases with age
• Associated with other autoimmune disease e.g. pernicious anaemia and vitiligo - Hashimoto’s thyroiditis
- Postpartum thyroiditis:
• Usually a transient phenomenon observed following pregnancy
• May cause hyperthyroidism, hypothyroidism or the two sequentially
• Thought to result from modifications to the immune system necessary in pregnancy and histologically is a lymphocytes thyroiditis (AUTOIMMUNE)
• Normally self-limiting but when conventional antibodies are found there is a high chance of this proceeding to permanent hypothyroidism
• Can be misdiagnosed as postpartum depression - why TFTs are essential! - Iatrogenic (caused by treatment or examination):
• Thyroidectomy - for treatment of hyperthyroidism or goitre
• Radioactive iodine treatment or external neck irradiation for head and neck cancer - Drug-induced:
• Carbimazole
• Lithium
• 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)
• Interferon - Iodine deficiency:
• Dietary iodine deficiency - results in goitre
• Patients have are euthyroid or hypothyroid, depending on the severity of iodine deficiency
• Mechanism is thought to be borderline hypothyroidism leading to TSH stimulation and thyroid enlargement in the face of continuing iodine deficiency
• Iodine deficiency is a problem in the Netherlands, Western pacific, India, SE Asia, Russia and part of Africa
what are the risk factors for hypothyroidism?
Being female Being older than age 60 Exposure to radiation in the neck Prior thyroid surgery Having a family history of thyroid disease Having a family history of autoimmune disease Having an autoimmune disease Being of Caucasian or Asian ethnicity
what is the brief pathophysiology of hypothyroidism?
- Underactivity is usually primary from disease of the thyroid but may be secondary due to hypothalamic-pituitary disease resulting in reduced TSH drive e.g. hypopituitarism
what are the key presentations of hypothyroidism?
Hoarse voice, Goitre, Constipation, Cold intolerant, dry skin, puffy face, bradycardic, ataxia
what are the signs of hypothyroidism?
- Bradycardia
- Reflexes relax slowly
- Ataxia (cerebellar)
- Dry, thin hair/skin
- Yawning/drowsy/coma
- Cold hands +/- temperature drop
- Ascites
- Round puffy face
- Defeated demeanour
- Immobile +/- Ileus (temporary arrest of intestinal peristalsis)
- Congestive cardiac failure
what are the symptoms of hypothyroidism?
- Hoarse voice
- Goitre
- Constipation
- Cold intolerant
- Weight gain
- Menorrhagia
- Myalgia, weakness
- Tired, low mood, dementia
- Myxoedema - accumulation of mucopolysaccharide in SC tissue
what is the first line investigations for hypothyroidism?
Thyroid function tests (serum TSH high = primary, serum TSH inappropriately low = secondary) (serum free T4 low = diagnostic)
what are the gold standard investigations for hypothyroidism?
Thyroid antibodies and organ specific antibodies e.g. TPO-Ab (thyroid peroxidase antibody) in Hashimoto’s
what are the other investigations for hypothyroidism?
- Blood tests:
• Anaemia: - Usually normochromic and normocytic
- May be macrocytic (sometimes due to pernicious anaemia)
- Or microcytic (in women, due to menorrhagia or undiagnosed coeliac disease)
• Raised serum aspartate transferase levels from muscle and/or liver
• Increase serum creatinine kinase levels associated with myopathy
• Hypercholesterolaemia
• Hyponatraemia due to an increase in ADH and impaired free water clearance
what are the differential diagnoses for hypothyroidism?
Non- thyroid illness, endocrine/autoimmune conditions such as T1DM, haematological conditions such as anaemia
how is hypothyroidism managed?
- Lifelong thyroid hormone replacement e.g. ORAL LEVOTHYROXINE (T4)
• In patients with ischaemic heart disease use with caution and start on lower dose
• Aim is normal TSH conc. which will be achieved by levothyroxine - but don’t give too much so as to completely suppress TSH as this carries risk of AF and osteoporosis
how is hypothyroidism monitored?
- Primary hypothyroidism:
• Dose is titrated until TSH normalises
• Check T4 levels 6-8 weeks after dose adjustment - Secondary hypothyroidism:
• TSH will always be low
• T4 is monitored
what are the complications of hypothyroidism?
• Myxoedema coma:
- Severe hypothyroidism (REDUCED T4) that may rarely present with confusion and coma - particularly in elderly
- Typical features include hypothermia, cardiac failure, hypoventilation, hypoglycaemia and hyponatraemia
- MEDICAL EMERGENCY and given IV/ORAL T3 & glucose infusion as well as gradual rewarming
