MEDizzy - A 45-year-old man reports to his primary care physician that

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A 45-year-old man reports to his primary care physician that his wife has noted coarsening of his facial features over several years. In addition, he reports low libido and decreased energy. Physical examination shows frontal bossing and enlarged hands. An MRI confrms that he has a pituitary mass. Which of the following screening tests should be ordered to diagnose the cause of the mass?

ExplanationFunctional pituitary adenoma presentations include acromegaly, as in this patient; prolactinomas; or Cushing syndrome. Hypersecretion of growth hormone underlies this syndrome in patients with pituitary masses, although ectopic production of growth hormone, particularly by tumors, has been reported. Because growth hormone is secreted in a highly pulsatile fashion, obtaining random serum levels is not reliable. Thus, the downstream mediator of systemic efects of growth hormone, insulin-like growth factor-1 (IGF-1), is measured to screen for growth hormone excess. IGF-1 is made by the liver in response to growth hormone stimulation. An oral glucose tolerance test with growth hormone obtained at 0, 30, and 60 minutes may also be used to screen for acromegaly because normal persons should suppress growth hormone to this challenge. Serum prolactin level is useful to screen for prolactinomas, and 24-hour urinary free cortisol and ACTH assay are useful screens for Cushing disease.