Question

Bertha is a 71-year-old woman who takes daily medication for Hashimoto thyroiditis. Last winter, she developed pneumonia. Although she did her best to run errands for her husband, she got tired easily and needed to rest frequently. One day, after shoveling the snow outside, her husband came inside to find Bertha lying on the sofa covered in blankets. Her face appeared puffy and her eyelids hung. When he spoke to her, Bertha’s voice was hoarse and her words did not make sense to him. Her respirations were also shallow and slow. Suspecting low thyroid hormone levels were causing the signs, her husband called for an ambulance.

1. When testing for hypothyroidism, why is the free T4 level an important measurement? What would the TSH and T4 test results indicate in someone with primary hypothyroidism?
2. Using your knowledge of the function of thyroid hormone in the body, explain why Bertha’s respiratory rate was decreased? Why might pleural effusion be present in someone with hypothyroidism?
3. What factors in Bertha’s history leave her susceptible to myxedematous coma? What are the physiologic aspects involved in myxedematous coma?

Answer 1

Question: When testing for hypothyroidism, why is the free T4 level an important measurement? What would the TSH and T4 test results indicate in someone with primary hypothyroidism?

Answer: The free T4 test is important because it measures the level of serum T4 that is unbound and readily available to enter cells. In an individual with primary hypothyroidism, one would expect a decrease in T4 and an increase in TSH levels. This would indicate the inability for the thyroid to produce T4 and the hyperfunction of the anterior pituitary in an attempt to stimulate the thyroid.

Questions: Using your knowledge of the function of thyroid hormone in the body, explain why Bertha’s respiratory rate was decreased? Why might pleural effusion be present in someone with hypothyroidism?

Answer: Thyroid hormone acts to maintain metabolic rate in the body. When metabolism is generated by thyroid hormone, both oxygen consumption and the production of metabolic wastes increase. The respiratory system is therefore stimulated to ensure homeostasis by adequate uptake of oxygen and elimination of carbon dioxide. Bertha's hypothyroidism lowered metabolic activity and therefore respiratory function. Myxedema involves the presence of a mucopolysaccharide substance in the tissues and edema throughout the body. The fluid accumulation occurs in not only the interstitial spaces but also the pericardial and pleural spaces.

Question: What factors in Bertha’s history leave her susceptible to myxedematous coma? What are the physiologic aspects involved in myxedematous coma?

Answer: Bertha is elderly and has likely had thyroid dysfunction for some time. Exposure to cold is also considered a precipitating factor to myxedema coma. The physiologic aspects of myxedema coma involve carbon dioxide retention and hypoxia due to hypoventilation. Metabolic dysfunction leads to fluid and electrolyte imbalances, hypoglycemia, and lactic acidosis. Seriously depressed metabolic function also contributes to hypothermia, cardiovascular collapse, and coma.