A 34-year -old woman has a 3-month history of nervousness, tremor, palpitations,

Question

A 34-year -old woman has a 3-month history of nervousness, tremor, palpitations, increased sweating, and discomfort with heat. She had lost 15 pounds despite increased food intake. She also noted muscle weakness and easy fatigability with exercise to which she was ordinarily accustomed. She had missed two consecutive menstrual periods. On physical examination, pulse was 110 beat/min and respirations were 20/min. Her skin was warm and moist, her speech was rapid her gaze had a stare quality, and her movements were hyperkinetic. She exhibited a tremor and very rapid reflexes, and she was unable to rise without assistance from a squatting position. The cardiac impulse was hyperdynamic, and the thyroid gland was diffusely enlarged. Laboratory studies showed a total serum T4 level of 26 ug/dl (normal 5 to 12), a free T4 of 4.2 ng/dl (normal 0.8 to 2.4), and serum TSH of 0.01 mIU/ml (normal 0.5 to 5). A 24-hour uptake of radioactive iodine was 70% (normal 8% to 30%). The patient was treated with a thiouracil drug. Four weeks later her symptoms had improved, and serum T4 had decreased further to 11 ug/dl. However, after 12 weeks of the same dose of the thiouracil drug, serum T4 had decreased further to 4 ug/dl, and she complained of the recurrence of fatigue, lethargy, and intolerance to cold. Her weight had increased 20 pounds to a level above her usual healthy weight. Resting pulse was 54 beats/min. the thyroid gland, which had began to decrease in size with drug treatment, had now grown even larger than before treatment.

by what mechanisms did an excess of thyroid hormone cause the various symptoms and physical findings this patient exhibited?

Why was her TSH so low?

What would you expect her TSH levels to be after 12 weeks of treatment?

Before treatment began how do you think her oxygen consumption would compare to the normal expected value?

What is the mechanism of action of the thiouracil drug?

Why did the thyroid gland re-enlarge?

Explanation / Answer

Hyperthyroidism or and overactive thyroid can cause weight loss, nervousness, tremor, palpitations, high pulse rate, and feeling of high heat. High thyroid has caused high rate of protein degradation in comparison of protein systhesis causing fatigue and muscle weakness. Low TSH can be caused by Hyperthyroidism. Initially the dose of drug was beneficial in recovery but continuous supression of thyroid hormone by the drug, caused Hypothyroidism (low levels of thyroid hormone). Basal metabolic rate also decreased causing weight gain. Insufficient amount of heat production in body caused cold intolerance. Before treatment began, she had hyperthyroidism. She was spending more calories than the amount of energy produced in body. High thyroid hormone had increased the metabolic rate of oxygen consumption. Body required more oxygen than available. At the beginning when the drug was administered it was continuously lowering the thyroid hormone in the body. But when the thyroid hormone production was continuosly supressed by the drug, it resulted into extremely lower levels of thyroid hormone. Thyroid gland enlarged in beginning due to hyperthyroidism. But later on it enlarged due to trophic action of excessive TSH acting through thyroid plasma membrane receptors to stimulate protein synthesis.

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