USMLE® Step 1 style questions USMLE
A 41-year-old woman comes to her outpatient provider because of skin changes that began three-months ago. She has noticed increased bruising and the development of purple-red stretch marks on the abdomen. Past medical history is notable for asthma, for which she intermittently uses a budesonide inhaler. She smokes half-a-pack of cigarettes per day. In the office, her temperature is 37.7°C (99.9°F), pulse is 71/min, respirations are 19/min, and blood pressure is 142/85 mmHg. Physical exam confirms the presence of ecchymoses and abdominal striae. Laboratory testing reveals the following findings:
|Fasting glucose||137 mg/dL|
|24-hour urine cortisol*||72 µg/day|
|Serum ACTH**||35 pg/mL|
*Normal range: 4-40 µg/day
**Normal range: 5-20 pg/mL
The serum cortisol levels are significantly reduced in response to a high-dose of dexamethasone. Which of the following is the most likely underlying pathophysiology for this patient’s condition?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS, Marisa Pedron, Jake Ryan, Robyn Hughes, MScBMC, Brittany Norton, MFA, Antonia Syrnioti, MD
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 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.
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.
Pituitary adenomas are benign tumors that occur in the pituitary gland. They vary depending on their size and the type of hormones they produce. Some pituitary adenomas do not produce any hormones and are referred to as non-functioning adenomas, while others produce hormones that can cause a wide range of symptoms.
Common symptoms include headaches, visual disturbances, fatigue, and changes in sexual function or menstrual cycles. The most common types involve lactotrophs that make prolactin, somatotrophs that make growth hormones, and corticotrophs that make ACTH. They are usually diagnosed by checking hormone levels and obtaining an MRI and are treated with medications or surgery.
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