Hyperthyroidism

Essentials

• In a hyperthyroid patient, TSH concentration is below reference range (often unmeasurable), and free T4 and/or free T3 concentrations are increased.
• As a general rule, patients with hyperthyroidism are referred to a specialist in internal medicine or an endocrinologist for assessment.
• Start a beta-blocker and also antithyroid medication already at referral to a specialist when the diagnosis of hyperthyroidism is clear. Remember to inform the patient concerning the risk of agranulocytosis associated with antithyroid medication.
• Patients with thyroid eye disease (in Basedow's [Grave's] disease only Graves' Ophthalmopathy) or with pregnancy-induced hyperthyroidism are promptly referred to a specialist.
• Hyperthyroidism is always treated. In uncertain cases, begin with a beta-blocker only.
• Depletion of hormone storages that is associated with an inflammatory state is not treated with antithyroid drugs (e.g subacute thyroiditis Subacute Thyroiditis).
• The thyroid gland is palpated in order to estimate its size, whereasultrasonography has no place in the diagnostics of hyperthyroidism.

Causes

• Basedow's disease (Graves' disease)
  • The most common cause; concentration of TSH receptor antibodies increased
  • Age at onset most commonly 30-40 years. The majority of patients are women.
  • Overactivity of the thyroid gland is often substantial.
• Overactive (toxic) multinodular goitre
• Overactive adenoma
• Other causes
  • Overdosage of thyroxine
  • Iodine-containing substances, especially amiodarone http://www.dynamed.com/condition/amiodarone-and-other-drug-induced-thyroid-disorders#GUID-6D6A8971-AA3E-4D1F-B501-846F58BEB26E; causes typically thyrotoxicosis from destructive thyroiditis (TSH < reference range and free T4 > reference range) which requires corticosteroid treatment. Basedow's hyperthyroidism triggered by amiodarone is rarer. There are also mixed forms of the aforementioned conditions. Can also cause hypothyroidism. Iodine has a long half-life.
    • Contrast-enhanced CT scan may also trigger hyperthyroidism.

Symptoms

• General symptoms
  • Hypersensitivity to heat and sweating
  • Fatigue, muscular weakness, deterioration of general condition
  • Palpitations, hand tremor
  • Weight loss, increased bowel motility
  • Thirst, polyuria
  • Disturbances in menstrual cycle
• Thyroid gland is often enlarged.
• Skin symptoms
  • Warm and moist skin
• Psychological symptoms
  • Lability, nervousness, irritability, sleeplessness
• Cardiac symptoms
  • Tachycardia and arrhythmias, particularly atrial fibrillation
• GI symptoms
  • Increased bowel function, diarrhoea, weight loss even if the appetite is good
• Ophthalmopathy in Basedow's disease only
  • Other types of ocular symptoms occur in many other patients with hyperthyroidism.
• Symptoms vary between patients. The elderly are often monosymptomatic (e.g. atrial fibrillation, fatigue, weight loss, worsening of angina pectoris, exertional dyspnoea alone) or their symptoms are masked (those already on beta-blocker treatment).

Diagnosis

• The patient has symptoms compatible with hyperthyroidism.
• The thyroid gland is palpated.
• TSH below and free T4 (FT4) above reference range http://www.dynamed.com/condition/hyperthyroidism-and-other-causes-of-thyrotoxicosis-37#THYROID_FUNCTION_TESTS.
• Increased TSH receptor antibody concentration confirms the underlying Basedow's disease http://www.dynamed.com/condition/hyperthyroidism-and-other-causes-of-thyrotoxicosis-37#THYROID_ANTIBODIES.
• If TSH is < 0.1 and FT4 is normal, FT3 is tested to identify T3 hyperthyroidism.
• If TSH is below reference range but both FT4 and FT3 are normal, the patient has subclinical hyperthyroidism. The thyroid parameters are checked after e.g. 3 months. If TSH concentration is only slightly decreased (0.1-0.4 mU/l) and the patient is symptomless, monitoring is sufficient. Principles for referring the patient to specialized care for assessment:
  • Repeated measurement of TSH is always necessary. A single measurement of TSH level of < 0.1 mU/l is not sufficient.
  • If TSH is persistently < 0.1 mU/l and the patient is over 60 years of age, refer him/her for assessment even if he/she would be asymptomatic.
  • If TSH is persistently < 0.1 mU/l or repeatedly mildly decreased (0.1-0.4) and the patient has goitre, symptoms of hyperthyroidism, atrial fibrillation or some other cardiac disease or osteoporosis, refer him/her for assessment.
  • Advanced age speaks for the need of assessment.

Treatment principles

• All patients are treated to euthyroid state with antithyroid medication (may be started in primary health care).
• The actual treatment strategy is decided in specialized care and may consist of
  • long-term antithyroid therapy (12-18 months)
  • radioiodine treatment
  • surgery.
• The choosing of treatment approach is influenced by the size of the thyroid gland, possible earlier thyroid surgery, possible eye symptoms, pregnancy and breast-feeding, patient's age and possible other severe diseases.
• Long-term antithyroid medication and radioiodine treatment are good alternatives when the thyroid gland is small.
• A very large thyroid gland is operated on.
• Radioiodine treatment may worsen thyroid eye disease.
• In overactive (toxic) multinodular goitre, permanent treatment results cannot be expected with antithyroid medication.
• Patients with mild hyperthyroidism and good general condition may be started immediately on radioiodine with beta-blocker cover alone; other patients should first be made euthyroid with a short course of antithyroid medication.

Pharmacotherapy

Notes on different treatment modes