A 41-year-old man comes to the office due to a 4-month history of fatigue, headache, weight loss, sweating, and palpitations. He is otherwise healthy and takes no medications. He does not use tobacco, alcohol, or illicit drugs. Physical examination reveals lid lag and a fine hand tremor. Neck examination reveals mild, diffuse enlargement of the thyroid gland. Laboratory results are as follows: Which of the following is the most likely cause of this patient's disorder?

Question

A 41-year-old man comes to the office due to a 4-month history of fatigue, headache, weight loss, sweating, and palpitations.  He is otherwise healthy and takes no medications.  He does not use tobacco, alcohol, or illicit drugs.  Physical examination reveals lid lag and a fine hand tremor.  Neck examination reveals mild, diffuse enlargement of the thyroid gland.  Laboratory results are as follows:  Which of the following is the most likely cause of this patient's disorder?

Quizplus · Accepted Answer

11ec160b_3caf_5f17_9249_e7f2ef94503f_MD0001_00 The hypothalamus-pituitary-thyroid axis functions as follows: Thyroid hormone is released primarily as thyroxine (T4), with deiodination to triiodothyronine (T3) (the more active form) in peripheral tissues. Synthesis of thyroid hormone is driven by TSH secretion from the pituitary. TSH is regulated by thyrotropin-releasing hormone (TRH) from the hypothalamus. Secretion of both TRH and TSH is subject to negative feedback by T3. Hyperthyroidism typically presents with fatigue, weight loss, and palpitations associated with elevated thyroid hormone levels. Hyperadrenergic signs (eg, lid lag, tremor) are also common. Most patients have primary hyperthyroidism (ie, intrinsic thyroid disorder with increased thyroid hormone release); TSH is low due to feedback suppression. However, this patient has an elevated TSH, suggesting a pituitary etiology (ie, secondary hyperthyroidism). The most common cause of secondary hyperthyroidism is a TSH-secreting pituitary adenoma. The excess TSH causes generalized hypertrophy of the thyroid gland, manifesting as a diffuse goiter. (Choice A) Most thyroid hormone is transported bound to plasma proteins, primarily thyroxine-binding globulin (TBG). Estrogen (eg, pregnancy, oral contraceptives) causes increased production of TBG, which lowers free thyroid hormone levels. A brief rise in TSH subsequently increases production of thyroid hormone to saturate the increased TBG binding sites, and the patient returns to a euthyroid state. Total T3 and T4 are elevated, but TSH and free hormone levels are normal. (Choices B and C) Graves disease is caused by autoantibodies that activate the TSH receptor and induce thyroid hormone production. Painless thyroiditis is characterized by autoimmune destruction of thyroid follicles with release of preformed thyroid hormone. Both conditions cause hyperthyroidism with elevated thyroid hormone levels, but TSH is suppressed by feedback inhibition. (Choice E) Thyroid cancer typically presents with a hard, asymmetric goiter. Adjacent thyroid tissue may be compressed and nonfunctional, but the contralateral lobe can usually compensate and patients are typically euthyroid. Thyroid follicular tumors may occasionally cause hyperthyroidism due to autonomous thyroid hormone production, but TSH is suppressed. Educational objective: The most common cause of secondary hyperthyroidism is a TSH-secreting pituitary adenoma. In addition to hyperthyroid symptoms, TSH causes generalized hypertrophy of the thyroid gland (diffuse goiter). Laboratory evaluation shows elevated levels of thyroid hormone (triiodothyronine and thyroxine) and TSH.

A 41-Year-Old Man Comes to the Office Due to a 4-Month