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