Michael is a thirty year old salesman who spends approximately 4 days each week traveling to visit with customers in his region. During his routine physical he casually mentions to his physician that he seems to be sweating more profusely than normal and most rooms that once were comfortable are now too “hot”. He thought that it was simply due to the change in seasons and companies being slow to turn down the thermostats from the winter temperatures, however this problem seems to persist even when he is at home. A room that his wife and children find to be comfortable causes him to sweat profusely. Michael also reports that he seems to be loosing weight even though his appetite has increased. He also complains that he has a shortened attention span and that he always wants to be moving around. Despite the fact that he feels fatigued, Michael claims to have difficulty sleeping and seems to have more frequent bowel movements, occasionally accompanied by diarrhea. The physician checks Michael’s medical history and finds that indeed he has lost 15 pounds since his last physical. Wanting to rule out the possibility of infection with the human immunodeficiency virus (HIV), the physician asks Michael questions about his sexual history and practices and finds that he is not at risk for HIV infection. Also in checking his chart, the physician finds that Michael has a negative history for chronic illnesses, does not smoke, and has a low risk for cardiovascular disease. He does however have a positive family history for autoimmune diseases. His father suffers from idiopathic thrombocytopenia, his mother has been diagnosed with rheumatoid arthritis and his oldest sister was recently diagnosed with systemic lupus erythematosus.
Results of Michael’s physical examination were within normal ranges with the exception of the following: he demonstrated tachycardia, loud heart sounds, and apparent cardiac arrhythmia accompanied by slight hypertension. The arrhythmia was confirmed by the electrocardiogram to be supra-ventricular in origin. Michael’s eyeballs appeared large and protruding and his hair was fine and soft. He was also beginning to demonstrate some degree of alopecia. Michael was also observed to have palmar erythema. Palpation of the neck revealed the presence of goiter. Results of blood tests indicated elevated concentrations of thyroid hormones (thyroxin and triiodothyronine),hypercalcemia, and decreased circulating concentrations of lipids. Based on the physical characteristics and the results of the blood tests, Michael’s physician suspected that Michael was suffering from some form of hyperthyroidism and sent him to an endocrinologist to confirm the initial diagnosis.
Following the initial consultation and examination, the endocrinologist ordered tests to determine whether Michael was indeed hyperthyroid. The test results indicated an elevation in the concentration of thyroid hormones in the blood and the presence of thyroid-stimulating antibodies. These antibodies specifically stimulate the thyroid gland by binding with the thyroid stimulating hormone receptor located on the plasma membrane of the follicular cells of the thyroid gland. Based on these results, the endocrinologist concluded that Michael had Grave’s disease, a form of hyperthyroidism believed to be autoimmune in nature. Michael was presented with a number of possible treatment options. These included treatment with chemicals (propylthiouracil and methimazole) that decrease the production of thyroid hormones by the thyroid gland, radio-isotopic destruction of the thyroid gland by the use of 131I, and surgical removal of the thyroid gland. After considering all the options, especially the possible effects of radiation on gamete development, Michael chose surgery. Following successful surgery, Michael was prescribed synthetic thyroid hormone to ensure that his body was receiving adequate thyroid hormone and told to return within 2 months for a follow-up evaluation of circulating thyroid hormone concentrations. He was also cautioned to carefully monitor his calcium intake.
question :Why would an imbalance in thyroid hormones have such a widespread effect on the body? Why was goiter observed in Michael’s case? Given that Michael and his wife may want to have more children, why was radio-isotopic, for the destruction of the thyroid gland, ruled out?