Case Study, Chapter 41, Disorders of Endocrine Control of Growth and Metabolism
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 (Learning Objectives 6 and 7).
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?
Expert Solution Preview
Introduction:
Hypothyroidism is a condition characterized by an underactive thyroid gland, leading to reduced production of thyroid hormones. In this case study, Bertha, a 71-year-old woman with Hashimoto thyroiditis, presented with symptoms suggesting hypothyroidism, such as fatigue, hoarseness, edema, and altered mental status. To understand the underlying pathophysiology and implications in this scenario, we will address three questions related to hypothyroidism.
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?
The free T4 level is an important measurement when testing for hypothyroidism because it reflects the bioavailable, unbound portion of thyroxine (T4) in the blood. Unlike total T4, which includes both bound and unbound fractions, free T4 provides a more accurate assessment of thyroid function.
In someone with primary hypothyroidism, the TSH (thyroid-stimulating hormone) level is typically elevated due to the unmet demand for thyroid hormone. The hypothalamus-pituitary-thyroid axis responds to low levels of circulating T4 by increasing TSH secretion, aiming to stimulate the thyroid gland’s function. Elevated TSH levels are indicative of primary hypothyroidism.
On the other hand, the T4 test results in individuals with primary hypothyroidism will reveal decreased levels of thyroxine. This occurs due to the impaired thyroid gland’s ability to synthesize and release an adequate amount of thyroid hormones, resulting in an overall reduction in T4 circulating levels.
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?
Thyroid hormone plays a crucial role in regulating the body’s metabolism, including respiratory function. Decreased thyroid hormone levels, as observed in hypothyroidism, can lead to a decreased respiratory rate. This occurs due to a decreased metabolic rate, resulting in reduced oxygen consumption by the tissues. Consequently, the body adapts by decreasing the respiratory rate and depth, aiming to preserve oxygen and minimize carbon dioxide production.
In individuals with hypothyroidism, pleural effusion may be present. Pleural effusion refers to an accumulation of excess fluid in the pleural space, which separates the lungs from the chest wall. Hypothyroidism can lead to impaired lymphatic drainage and reduced plasma colloid osmotic pressure, contributing to the development of pleural effusion.
3. What factors in Bertha’s history leave her susceptible to myxedematous coma? What are the physiologic aspects involved in myxedematous coma?
Several factors in Bertha’s history make her susceptible to myxedematous coma, a severe manifestation of hypothyroidism. These include her age, the presence of Hashimoto thyroiditis, recent infection (pneumonia), and physical exertion (shoveling snow). The combination of these factors can exacerbate the underlying thyroid dysfunction, leading to a critical reduction in thyroid hormone levels.
Myxedematous coma is characterized by severe hypothyroidism resulting in multi-organ dysfunction and altered mental status. Physiologically, this condition is associated with slow mentation, decreased cardiac output, hypothermia, hypoventilation, and hyponatremia. These manifestations occur due to the impaired metabolic processes caused by severe deficiency of thyroid hormones.
In conclusion, understanding the pathophysiology and clinical manifestations of hypothyroidism is crucial for evaluating and managing patients like Bertha. By considering the importance of free T4 levels, respiratory effects of thyroid hormones, and factors leading to myxedematous coma, healthcare professionals can effectively diagnose and intervene in cases of hypothyroidism.
