USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 31-year-old woman comes with her husband to the emergency room complaining of palpitations for the past three weeks. They have started to increase in intensity and frequency over the past two days, and have been accompanied by periods of sweating and tremulousness. Her husband notes that she has been bumping into walls and the edges of tables more recently, and had damaged the fence lining their driveway when backing out in their car three days ago. Her temperature is 36.9°C (98.5°F), pulse is 114/min, respirations are 18/min, and blood pressure is 142/78 mm Hg. Physical examination shows a diffusely enlarged goiter, fine resting tremor in both arms and diaphoresis. An ECG is obtained and shows sinus tachycardia. Which of the following is the most likely diagnosis?
Normally, the pituitary is a pea-sized gland, hanging by a stalk from the base of the brain.
It sits just behind the eyes near the optic chiasm, which is where the optic nerves cross.
The anterior pituitary, which is the front of the pituitary gland, contains a few different types of cells, each of which secretes a different hormone.
The second largest cell group are the corticotrophs which secrete adrenocorticotropic hormone, or ACTH for short.
A smaller cell group are the lactotrophs which secrete prolactin.
There are also thyrotrophs which are cells that secrete thyroid stimulating hormone, or TSH which goes on to stimulate the thyroid gland.
And finally, there are also gonadotrophs which secrete two gonadotropic hormones - luteinizing hormone, or LH, and follicle-stimulating hormone, or FSH, both of which go on to stimulate the ovaries or testes.
In pituitary adenomas, one of these cells mutates and becomes neoplastic, meaning that it starts dividing uncontrollably and over time it forms a tumor.
But these cells don’t invade neighboring tissues, so this is considered a benign tumor rather than a malignant one.
Pituitary adenomas can be classified by their size, adenomas smaller than 1cm are called microadenomas, and those larger than 1cm are called macroadenomas.
Macroadenomas can also compress optic nerves as they cross at the optic chiasm.
Finally, the compression can also affect other healthy pituitary cells and interfere with their ability to make hormones.
Pituitary adenomas that secrete hormones are called functional adenomas, whereas those that don’t are called non-functional adenomas.
Functional pituitary adenomas are divided into a few different types depending on the cells that they arise from and the hormone these cells produce.
The most common type of pituitary adenoma is a prolactinoma which arises from lactotrophs that make prolactin.
In men, excess prolactin causes a low libido - a low sex drive and gynecomastia or breast enlargement.
The second most common type of pituitary adenoma arises from somatotropes that make growth hormone.