Hyperthyroidism (Myxoedema)

Introduction

Hypothyroidism refers to subnormal amounts of thyroid hormones in the circulation, and the clinical features associated with it.

Aetiology

May be primary or secondary
Primary hypothyroidism is more common and:

  • Is probably an autoimmune disease; which may occur as a sequel to Hashimoto’s thyroiditis.
  • Post therapeutic hypothyroidism (medical or surgical)

Secondary hypothyroidism:

  • Occurs when there is failure of the hypothalamic-pituitary axis due to Deficient secretion of TRH from the hypothalamus.

Or:

  • Lack of secretion of TSH from the pituitary

Clinical features

Generally in striking contrast to those of
hyperthyroidism; may be quite subtle, with an insidious onset.
In adults:

  • Dull facial expression, slow speech and poor memory
  • Puffiness of the hands, feet and face
  • Lethargy and fatigue
  • Thinning, dryness and loss of hair
  • Hypothermia
  • Bradycardia
  • Reduced systolic and increased diastolic blood pressure
  • Weight gain
  • Decreased reflexes
  • Constipation
  • Menstrual abnormalities

In infants:

  • Mental and physical retardation
  • If not corrected, cretinism

Differential diagnoses

  • Endogenous depression
  • Reactive depression

Complications

  • Myxoedema coma
  • Cretinism in the young

Investigations

  • Total serum T and T levels
  • TSH stimulation test
  • TRH test

Treatment objectives

  • Establish cause
  • Establish the severity of hypothyroidism
  • Prevent complications
  • Restore normal body functions

Drug treatment

Replacement therapy

Levothyroxine sodium
(thyroxine sodium)

  • Adult: initially 20 – 100 micrograms (50  Mmicrograms for those over 50 years) orally daily, preferably before breakfast
  • Adjusted in steps of 50 micrograms every 3-4 weeks until metabolism normalizes (usually 100-200 micrograms daily)
  • Child
    • 1 month – 2 years: initially 15
      micrograms/kg orally once daily, adjusted in steps of 25 micrograms daily every 2 – 4 weeks until metabolism normalizes
    • 2 – 12 years: initially 5-10 micrograms/kg once daily adjusted in steps of 25 micrograms daily every 2-4 weeks until metabolism normalizes
    • 12 – 18 years: initially 50 – 100 micrograms once daily, adjusted in steps of 50 micrograms daily every 3-4 weeks until metabolism
      normalizes (usual dose 100 – 200 micrograms
      daily

Or:

Liothyronine sodium (1- tri -iodothyronine  sodium)

  • Adult: initially 10 – 20 micrograms orally daily, gradually increased to 60 micrograms daily in 2-3 divided doses. Small initial doses in the elderly. In hypothyroid coma: 5- 20 micrograms by slow intravenous injection, repeated every 12 hours (as often as every 4 hours if necessary)

Alternatively:

  • 50 micrograms by slow intravenous
    injection initially then 25 micrograms every 8 hours, reducing to 25 micrograms daily
  • Child:
    • 12-18 years: 10 – 20 micrograms orally daily, gradually increased to 60 micrograms daily in 2-3 divided doses
    • In hypothyroid coma:
    • 1 month – 12 years: 2-10 micrograms by slow intravenous injection every 8 hours (up to every 4 hours if necessary); Reduce to 1 – 5 micrograms in patients with cardiovascular disease
    • 12 – 18 years: 5 – 20 micrograms, repeated every 12 hours] (up to every 4 hours if necessary). Reduce to 10 – 20 micrograms in patients with cardiovascular disease

Supportive measures

  • Treat anaemia, constipation and othercomplications as appropriate.
  • Immediate mechanical ventilation in myxoedema coma

Notable adverse drug reactions, caution

  • Thyroxine should not be used alone for long term replacement therapy
  • Monitor serum levels of hormones to ensure that patients are not exposed to cardiac risks

Prevention

  • Iodinated salt to prevent iodine
    deficiency