• Hypothyroidism

    by  • 19/07/2013 • Endocrine

    1. The clinical effect of decreased production of thyroid hormones
    2. Epidemiology: F>M (6>1), prevalence 1-5%, incidence 2/1000/y. most common from middle age onwards and associated with FH of a/i disease.
    3. p/c: mentally slow (=depression, psychosis [‘myxoedema madness’], cerebellar disturbances, deafness), facial puffiness, husky voice, bilateral carpal tunnel, slow relaxing reflexes, weigh gain, cold intolerance (risk of heat damage from heater [erythema ab igni], hair loss, dry thin skin, bradycardia, pericardial effusions, premature IHD, constipation, menstrual disturbances, amenorrhoea.
    4. Causes:
    5. Thyroid failure can be caused by disease of thyroid (=primary hypothyroidism), the pituitary gland (=secondary hypothyroidism) or the hypothalamus (=tertiary hypothyroidism).
    6. Primary (thyroid): common, seen in Europe/North America. Result of autoimmune disease…
    7. Autoimmune disease types:
      1. o Hashimoto’s thyroiditis = common, goitre present, familial, autoantibody to thyroglobulin and thyroid peroxidase.
      2. o Atrophic thyroiditis = common, no goitre, elderly, inhibitory autoantibody to TSH receptor.
      1. o Riedel’s thyroiditis: RARE! Woody sclerosis of thyroid, related to other sclerosing retroperitoneal fibrosis.
    1. Autoantibodies found in both, may have a FH of Addison’s, pernicious anaemia, or DM.
      1. o Hashimoto’s rarely causes pain in acute phase, and leads to transient hyperthyroidism
      2. o The most common cause WORLDWIDE is iodine deficiency due to poor dietary intake. Can lead to an endemic goitre (=Derbyshire neck)!
      3. o Iodine excess: chronic excess (linked to expectorant or amiodarone use) may cause hypothyroidism.
      4. o Post-thyrotoxicosis Tx: previous radio-iodine (131I), surgery, anti-thyroid drugs, (also lithium) to tx for hyperthyroidism (50% will be hypo at 10 years)!
    2. Ix:
      1. o Haem: FBC, if MCV 95-110fL = anaemia. If Hb <10g/dL suspect additional cause. If MCV <85fL = iron deficiency, if >115fL = pernicious anaemia.
      2. o TFT:
      3. o Low thyroxine (T4) and high TSH = primary hypothyroidism
      4. o Low or normal TSH = secondary/tertiary hypothyroidism
      5. o Cortisol: to exclude coexistent hypoadrenalism (=Addison’s disease or reduced ACTH reserve in secondary hypothyroidism)
      6. o Thyroid antibodies: positive peroxidase and thyroglobulin antibodies in Hashimoto’s thyroiditis and blocking TSH in atrophic thyroiditis
      7. o Other biochem: cholesterol will be raised, so may muscle ezymes (AST, CK).
      8. o ECG: brady, low voltage complexes
    3. Mx:
      1. o Thyroxine (T4) 50ug/d, increasing to 125-150ug/d, with dose titrated against clinical and biochemical TSH response to Tx.
      2. o Triiodothyronine (T3) can be started at lower doses, shorter half-life, may be useful in older patients and IHD pts (higher doses may provoke angina/MI)
    4. Complication of hypothyroidism:
      1. o Myxoedema coma: Rare, mortality >50%, p/c: hypothermia, coma, shares RFs with other causes of hypothermia (sedatives, age…)
      2. o Tx: IV T3 (20ug bolus, repeated 6-hourly). Thyroid disease may related to pituitary disease (suspect when Na is low) – hydrocortisone should be given (100mg bolus, repeated 6-hourly), until a diagnosis is made. 
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