Biology of Disease

Hypothyroidism (myxodema) is most common in women of 30–60 years of

age (Figure 7.19). Its clinical features include psychosis, diminished sweating,

hypokinesis, weight gain, muscle weakness, constipation, dry, cold skin and

dry hair, ischemic heart disease, bradycardia and menstrual irregularities.

The primary cause of hypothyroidism is a defect in the secretion of thyroid

hormones by the thyroid gland. In, for example, Hashimoto’s thyroiditis, an

autoimmune disease, there is destruction of thyroid tissue by antibodies

(Chapters 4 and 5 ) produced against the thyroid. Hypothyroidism may

also occur after surgery (postthyroidectomy) and following treatment with

antithyroid drugs. Congenital hypothyroidism occurs because of the failure of

the thyroid gland to develop normally during embryonic growth. If untreated,

this condition results in cretinism where the child suffers from mental

retardation, muscle weakness, short stature, neurological signs and is often

dumb and mute. Hypothyroidism may also arise due to iodine deficiency in

certain parts of the world. Secondary causes of hypothyroidism are linked to

the pituitary or the hypothalamus with defective secretions of TSH and TRH

respectively.

X]VeiZg,/ DISORDERS OF THE ENDOCRINE SYSTEM

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Figure 7.19 Schematic to show the clinical

features of myxodema.

Psychosis

Loss of outer third

of eyebrows

Sluggish behavior

Dry hair

Swollen and pendulous face

Gruff voice

Goiter

Diminished sweating

Ischemic heart disease, ECG

changes and bradycardia

Constipation

Carpel tunnel syndrome

Weight gain

Menstrual irregularities

Dry, cold skin, prone to

hypothermia

Muscular weakness

Diagnosis and Treatment of Thyroid Disorders

Investigating thyroid abnormalities involves measurements of serum

TSH as a first line test for thyroid function. Some laboratories also include

measurement of free T 4 and/or free or total T 3 in their first line screen.

Sensitive assays for measurement of TSH are readily available. Thyroid

stimulating hormone levels are increased in primary hypothyroidism,

normal in euthyroid individuals (those without thyroid disease) and low or

undetectable in hyperthyroidism.