Hypothyroidism Flashcards
Define hypothyroidism.
Hypothyroidism is a clinical state resulting from underproduction of the thyroid hormones thyroxine (T4) and triiodothyronine (T3).
How common is primary vs secondary hypothyroidism?
- Most cases (95%) are due to primary hypothyroidism, a failure of the thyroid gland to produce thyroid hormones.
- The remaining 5% of cases are due to secondary hypothyroidism, underproduction of thyroid-stimulating hormone (TSH) by the pituitary gland
How common is hypothyroidism?
Affects ~1-2% of women in the UK and is ~5-10 times more common in females than males
What is the aetiology of primary and secondary hypothyroidism?
Primary hypothyroidism
- Hashimoto’s thyroiditis - most common cause; autoimmune - women at x9 risk ; peak at 30-50yrs
- Subacute thyroiditis (de Quervain’s)
- Riedel thyroiditis
- After thyroidectomy or radioiodine treatment
- Drug therapy (e.g. lithium, amiodarone or anti-thyroid drugs such as carbimazole)
- Dietary iodine deficiency
- Radiotherapy of head/neck
- Toxin - biphenyls or resorcinol
- Rarely sarcoid/haemochromatosis infiltrative diseases
- Transiently - de Quervain’s thryoiditis, lymphocytic thyroiditis
Secondary hypothyroidism (i.e. pituitary related)
- Down’s syndrome
- Turner’s syndrome
- Coeliac disease
What are the risk factors for primary hypothyroidism?
- Iodine deficiency
- Female sex - Autoimmune (Hashimoto’s) thyroiditis, the most common cause of primary hypothyroidism in the US, is 8 to 9 times more common in women than men
- Middle age
- FH
- AI disorders
- Turner’s and Down’s syndrome
- Radiotherapy
- Amiodarone use
- Lithium use
- T1DM
- Infiltrative disease - sarcoidosis and haemochromatosis
- Iodine excess - iodine is thought to make thyroid tissue more antigenic
- Textile workers - exposure to polychlorinated and polybrominated biphenyls and to resorcinol
Name 3 drugs which can cause hypothyroidism.
lithium, amiodarone, aminoglutethimide, interferon alpha, thalidomide, stavudine, tyrosine kinase inhibitors, and anti-CD52 monoclonal antibodies
What are the effects of thyroid hormone?
T3 is the active form
- Liver - increased gluconeogenesis, cholesterol synthesis, fat oxidation/synthesis
- Tissue - fatty acid mobilisation
- Heart - increased heart rate (increased ionotropy and chronotropy)
- Pituitary - reduced TSH, increased GH
- Muscle - increased protein catabolism, glucose utilisation and fat oxidation
- Bone - growth and maturation and more resorption
What antibodies are present in autoimmune thyroiditis? What conditions can co-exist?
Thyroid is infiltrated with lymphocytes
Antibodies:
- antithyroid peroxidase 95%
- antithyroglobulin 60%
AI thyroiditis occurs in syndromes of multiple endocrine organ failure types 1 and 2, which can cause adrenal failure, hypoparathyroidism, diabetes mellitus (type 1), ovarian failure, vitiligo, and Sjogren’s syndrome.
What are the signs and symptoms of hypothyroidism?
General
- Weight gain
- Lethargy
- Cold intolerance
- Slow speech and movement
- Bradycardia, narrow pulse pressure due to diastolic hypertension
Skin
- Dry (anhydrosis), cold, yellowish skin
- Non-pitting oedema (e.g. hands, face like eyelid oedema)
- Dry, coarse scalp hair, loss of lateral aspect of eyebrows
Gastrointestinal
- Constipation
Gynaecological
- Menorrhagia
Neurological
- Decreased/delayed deep tendon reflexes
- Carpal tunnel syndrome
A hoarse voice is also occasionally noted.
What are the signs and symptoms of myxoedema coma?
- hypothermia
- hypotension and bradycardia
- thin and brittle hair
- periorbital oedema
- hyporeflexia
What investigations would you do for hypothyroidism?
- TSH- normal is 0.4-4.0mIU/L - elevated
Other:
- Free T4 - low; normal is 9-23picomol/L
- Anti-TPO - high
- FBC - a mild, normocytic anaemia sometimes
- Fasting blood glucose - hypothyroidism associated with T1DM so may be elevated
- Serum cholesterol - LDL elevated in hypothyroidism
How do you manage hypothyroidism?
Levothyroxine
- Start with 25mcg - for those >50yrs or with cardiac disease or severe hypothyroidism.
- Start 50-100mcg in uncomplicated patients
- Check 8-12weeks after changing dose
- Aim for TSH of 0.5-2.5mU/L
- In pregnancy increase by 25-50mcg
- Do not take with iron/calcium carbonate as this reduces absorption
What are the complications of hypothyroidism and its treatment ?
Hypothyroidism:
Resistant hypothyroidism - most likely due to non-adherence, and less often from drug interactions and co-existing illness.
Myxoedema coma - medical emergency with multi-organ failure and usually treated in an intensive care setting.
Complications in pregnancy
Overtreatment:
Hyperthyroidism
Angina - can be exacerbated with treatment
AF - overtreatment
Osteoporosis
What is the prognosis with hypothyroidism?
Generally excellent with full recovery upon adequate replacement of thyroid hormones.
The levothyroxine replacement dose may change over a period of years as the disease progresses
What other autoimmune condition’s is Hashimoto’s associated with?
Type I DM
Addison’s
Pernicious anaemia
Coeliac
Vitiligo
Also associated with the development of MALT lymphoma.
What is the management of subclinical hypothyroidism?
Many will never progress
