Critical Thinking

Thyroid hormone is essential for normal
development, differentiation, and metabolic balance (1). Hypothyroidism
is a common endocrine disorder affecting
1.4% to 2.0% of women and 0.1% to 0.2% of men. Typical symptoms are consistent with
declining metabolic functions and range from vague complaints of fatigue in
subclinical deficiency to overt clinical symptoms involving changes in
mentation and memory, lethargy, weight gain, cold intolerance, constipation,
and goitre enlargement of the thyroid gland. The
most common cause of hypothyroidism is destruction of the thyroid gland by
disease or as a consequence of attempts of various therapies to control
thyrotoxicosis. Primary hypothyroidism may also result from inefficient hormone
synthesis caused by inherited defective production, a deficient supply of
iodine or inhibition of hormonogenesis by various drugs and chemicals. In such
instances, hypothyroidism is typically associated with thyroid gland enlargement.

The
mental picture in patients with overt hypothyroidism usually is one of extreme
complacency. Memory is undoubtedly impaired, and attention and the desire to
think are reduced. The emotional level seems definitely low, and irritability
is decreased. Except in the terminal stage, reasoning power is preserved. In a
minority of patients, nervousness and apprehension are present. Cognitive tests
of patients with moderate to severe hypothyroidism indicate difficulties in
performing calculations, recent memory loss, reduced attention span, and slow
reaction time. Atypical
presentations such as weight loss, hearing impairment, tinnitus, and carpal
tunnel syndrome may occur, especially in the elderly (2, 3). Hypothyroidism may occur as a result of radioiodine
or surgical treatment for hyperthyroidism, thyroid cancer, or benign nodular
thyroid disease and after external beam radiation for non-thyroid-related head
and neck malignan­cies, including lymphoma (4).