A19-year-old woman who has always been healthy and maintained an average weight has lost 20lbs in the last 3 months, despite a voracious appetite. she complains of nervousness, sleeplessness, heart palpitations and irregular menstrual periods. she notes that she is "always hot" and wants the thermostat set lower than her roommates.
on physical examination, she was restless and had a noticeable tremor in her hands. at 5’8" tall, weighed only 110lbs. her blood pressure was 160/85 (normal is less than 120/less than 80), and her heart rate was 110 beats/min (normal 60-100 beats/min). she had a wide-eyed stare, and her lower neck appeared full; these characteristics were not present in photographs taken 1 year earlier.
based on her symptoms, the physician suspected that she had thyrotoxicosis, or increased circulating levels of thyroid hormones. however, it was unclear from the available information why her thyroid hormone levels were elevated. lab tests were performed to determine the etiology of her condition.
based on an understanding of the hypothalamic-anterior pituitary-thyroid axis, regulation of thyroid hormone secretion and the lab results, include or exclude (and explain why) each of the following four potential causes of this patient’s thyrotoxicosis:
a. increased secretion of thyrotropin-releasing hormone (trh) from the hypothalamus
b. increased secretion of thyroid-stimulating hormone (tsh) from the anterior pituitary
c. primary hyperactivity of the thyroid gland (i. e., grave’s disease)
d. ingestion of exogenous thyroid hormones (factitious hyperthyroidism)