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Endocrine Disorders

Endocrine disorders arise due to:

  • Hormonal Imbalance
    • Oversupply of Hormone (eg. tumour)
    • Deficiency (eg. congenital lack, damage)

Congenital Hypopituitarism

  • Definition: multiple pituitary hormone deficiency due to mutations of pituitary transcription factors
  • 1/3000-4000 live births
  • Manifestations:
    • Short stature, cognitive alterations, delayed puberty
  • Management:
    • Appropriate replacement hormone
    • adrenal, thyroid, gonadal

Congenital Adrenal Hyperplasia

  • Cause:
    • Genetic disorder (deficiency in the activity of enzyme required for the biosynthesis of glucocorticoids)
    • often CYP21 (also called 21 hydroxylase)
    • Results in lifelong adrenal insufficiency
    • may present as cardiovascular collapse
  • Management
    • Hydrocortisone
      • Suppresses ACTH and restores steroids
    • Fludrocortisone
      • Mineralocorticoid

Cushing's Syndrome

  • Excessive levels of glucocorticoids
  • Causes:
    • Glucocorticoid therapy
    • Cortisol production by adrenal tumour
    • ACTH produced by pituitary tumour
    • Adrenal carcinoma (in children)
  • Management:
    • Pituitary dependent - remove tumour
    • Adrenal dependent - remove tumour
    • Block corticosteroid production with ketoconazole or metyrapone
    • May require concurrent glucocorticoids

Thyroid Gland

  • Butterfly shaped structure in front of the trachea
  • Secretes 2 thyroid hormones: T3 and T4 (also called thyroxine)
  • Also secretes calcitonin

Thyroid Hormone Production

  • Thyrotropin releasing hormone (TRH) is released by the hypothalamus
  • acts on the anterior pituitary to stimulate the release of thyroid stimulating hormone (TSH)
  • Acts on the thyroid to produce T3 and T4

For more detail see: http://studyingmed.com/wiki/index.php?title=BGDB/Lectures/Structure_and_function_of_the_thyroid

Hypothyroidism

  • Low circulating levels of free T3 and T4
  • Historically, linked to low dietary iodine;
    • easily treated with dietary supplements
  • Endemic iodine deficiency in pregnant women
  • can lead to cretinism or goitre in the offspring
  • May arise due to:
    • autoimmune response where antibodies to TSH receptor inhibit the receptor function (no TSH) signalling
    • 131-I treatment, surgery for hyperthyroidism
  • Treatment is given to restore euthyroid state (normal thyroid function state), relieve symptoms and maintain growth and development
  • Before treatment is administered:
    • Thyroid function test - elevated TSH with low free T4
    • Consider secondary hypothyroidism (eg. low TSH, low T4 - due to pituitary or hypothalamic disease)
  • Thyroid Hormone replacement
    • T4 is converted to T3 inside cells
    • T4 is the replacement of choice due to its longer half-life (7days), oral availability and its negative feedback on the anterior pituitary (suppressing TSH)
    • Hormone replacement occurs daily and is often a lifelong therapy
    • It is important to monitor the therapy. TSH should be measured after 6 weeks after dose adjustments
    • Sideeffects are related to the actions of hormones (eg. tachycardia, sweating, weight loss)

Screening for Hypothyroidism in Newborns

  • Screening is done because there are often no signs
  • Involves a heel prick test, looking for high TSH
  • Replacement therapy should be started as soon as possible
  • Physical and mental development should also be monitored

Other Special Cases

  • Pregnancy
    • Monitor thyroid function each trimester
    • postpartum thyroid dysfunction may occur
  • Elderly
    • Maintenance dose required may be lower

Hyperthyroidism

  • High circulating levels of T3 and T4
  • most common cause is Graves disease
    • This is an autoimmune response to the TSH receptor causing overstimulation
  • other causes:
    • toxic multinodular goitre
    • toxic adenoma
    • sub-acute thyroiditis
  • Diagnosis is confirmed with thyroid function tests
    • Low TSH with high free T4/T3
  • Clinical Manifestations:
    • Enlargement of the thyroid gland (goitre)
    • Localised oedema
    • Swelling around the eyes, upper lid retraction
    • Clubbing of the fingers and toes
  • Treatment options:
    • surgery
      • subtotal thyroidectomy
      • effective in graves/multinodular goitre
      • antithyroid drugs and iodine given prior to surgery
      • Thyroid supplementation may be required post surgery
    • radiotherapy (131-I)
      • Useful in graves disease
      • selective uptake
      • half-life of 8 days
      • contraindicated in pregnancy
      • followed by antithyroid drugs for 3-6 months
      • risk of rendering a person hypothyroid
    • drugs
      • controls hyperthyroidism
      • used in conjunction with radiotherapy
      • also used to control disorder prior to surgery


Antithyroid Drugs

  • eg. Carbimazole, PTU
  • Action:
    • block thyroid hormone synthesis by inhibiting thyroid peroxidase
    • PTU also blocks the de-iodination of T4 to T3
  • Long term treatments
  • PTU t1/2 = 2 hours
  • Carbimazole t1/2 = 4-6 hours
  • Adverse Effects:
    • Vomiting
    • Anorexia
    • Itching, rash
    • Agranulocytosis
    • can cross placenta
  • Considerations:
    • Pregnancy (use lowest effective dose)
    • PTU is preferred
    • Can induce fetal hypothyroidism
    • Lactation - PTU preferred
  • Adjusted Regimen:
    • High dose for 3-4 weeks
    • Reduced dose by 50% to maintain function
    • Review every 4-6 weeks with gradual reduction
  • Block-replacement regimen
    • antithyroid drugs maintained at high dose long term
    • thyroxine added at 6 weeks to maintain euthyroid state
    • Follow up every 3 months
  • Other drugs can be used for symptomatic relief
    • beta blockers (contraindicated in asthma)
    • eye drops (lubrication)

Iodine Deficiency

  • Maternal and neonatal hypothyroidism, due to iodine deficiency remains the major preventable cause of mental retardation worldwide
  • Iodine deficiency can lead to goitre
  • Rates have been dramatically cut in the past due to the introduction of iodized table salt, but there are still places (including Australia) where iodine deficiency occurs

Summary

  • Treatment of hypothyroidism involves thyroxine replacement, with T4 drug of choice
  • Of particular concern in neonates
  • Treatment of hyperthyroidism may involve surgery, radiotherapy or drug treatment
  • Antithyroid drugs block the synthesis of thyroid hormone (PTU also prevents de-iodination of T4)
  • Several adverse effects may occur, including agranulocytosis
  • They should be used with care in pregnancy
  • Thyroid status should be regularly monitored
  • Thyroid disorders are relatively common