hyperthyroidism
HYPERTHYROIDISM
Hyperthyroidism is the overactivity of the thyroid gland resulting in excessive production of thyroid hormones.
Symptoms are of gradual onset.
Earliest signs may be emotional lability and motor hyperactivity; decline in school performance may also be noted.
Causes are autoimmune (Grave's disease), inappropriate stimulation by trophic factors, passive release of preformed thyroid hormone stores in response to infections, trauma, or other offensive factors inside the body, and extra-thyroidal sources.

Pharmacotherapy

Antithyroid Agents

  • Considered 1st-line treatment
  • 2 methods in treating hyperthyroid patients
    • Dose titration: Dose is reduced & titrated against thyroid function tests to achieve a euthyroid state
    • Block & replace regimen: Antithyroid agents are given in combination w/ thyroid preparation (eg thyroxine)
  • Effects: About 25% of patients remain euthyroid ≥5 years after antithyroid treatment
    • Remission is most likely to occur in the following patients: male, >13 years of age, w/ higher body mass index, small goiters & fairly elevated levels of T3
    • Relapse usually appears w/in 3-6 months after stopping the therapy
  • Usually takes 3-6 weeks for clinical response to be noticeable
    • 3-4 months to have adequate control
    • May use beta-blockers to control symptoms during this period, but not always needed

Beta-Blockers

  • Eg Propanolol, Atenolol, Metoprolol
  • Recommended for symptomatic treatment of hyperthyroidism especially in children w/ a heart rate (HR) of >100 bpm
  • Contraindicated in hyperthyroidism patients w/ bronchospastic asthma
    • Nadolol may be given to asthmatic hyperthyroidism patients w/ mild chronic obstructive pulmonary disease (COPD), symptomatic Raynaud’s phenomenon, or those whom HR control is essential
  • Atenolol is the most used beta-blocker because of its cardioselective property, thus less risk for bronchospasm
  • Esmolol is preferred over other beta-blockers for older intensive care unit (ICU) patients w/ thyroid storm/severe thyrotoxicosis

Thionamides

Carbimazole

  • Inhibit thyroid hormone biosynthesis by decreasing iodide oxidation & iodination of tyrosine
  • Fewer tablets are needed for initial treatment compared w/ Propylthiouracil (PTU)

Methimazole

  • Methimazole is preferred over PTU because of less adverse effects 
    • 10-fold more potent on wt basis than PTU
  • Recommended as first-line antithyroid treatment in pediatric patients

Propylthiouracil (PTU)

  • Blocks the conversion of T4 to T3 in thyroid gland & peripheral tissues, also inhibits thyroid hormone biosynthesis by decreasing iodide oxidation & iodination of tyrosine

Surgical Intervention

  • Patients may undergo subtotal, near-total or total thyroidectomy
  • Effects: Up to 97% cure rate when performed by experienced surgeons
  • Indications:
    • Sufficient cooperation for medical therapy is not possible
    • Adequate trial of antithyroid agents has failed to cause permanent remission
    • Intolerance to severe side effects of antithyroid drugs
    • Large thyroid gland size (>80 g)
    • Need for immediate disease control
    • <5 years of age
    • For very young patients intolerant to radioactive iodine therapy
  • Potential complications: Hypoparathyroidism, damage to recurrent laryngeal nerve
  • Iodine therapy rather than surgery is more advisable for patients w/ thyroid enlargement of >80 g

Prior to Surgery

  • Restoration of euthyroidism
    • Antithyroid drug treatment over 2-3 months prior to surgery
    • Iodide (eg saturated solution of potassium iodide) is added in the regimen for 2 weeks once euthyroid state is achieved; given to decrease the vascularity of the thyroid gland

Permanent Hypothyroidism

  • Patients may become hypothyroid
  • Treat w/ T4 replacement

Radiotherapy

  • Effective & relatively safe in patients >10 years
    • May be considered in patients who relapse after medical therapy
  • Pretreatment w/ antithyroid agents is not required
  • Full effects of radioactive iodine therapy may not be complete for 1-6 months, use of beta-blocker & antithyroid agents may be recommended
  • Patients may expect long-term thyroid replacement w/ thyroxine (T4)
  • Frequency of radioactive iodine therapy is reduced due to theoretical risk of malignancy or genetic damage
  • Instructions on radiation safety precautions immediately following treatment
    • Close & prolonged physical contact w/ other people should be avoided for 3 days
    • Caregiver is advised to have the patient take a break from daycare or school for 2 weeks

Ophthalmopathy

  • Usually resolves gradually & independently of hyperthyroidism
    • May resolve when patient becomes euthyroid
  • Some symptoms may not resolve especially if the symptoms are caused by autoimmune reaction against fibroblasts or muscles of the orbit
  • May be treated w/ high-dose Prednisone
  • Surgical decompression of orbits or orbital radiotherapy may also be done
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