USMLE Step 1 – Question of the Week #2

A 38-year-old man presents to physician with complains of excessive thirst and excessive passage of urine for last one week. He also mentions that he has to get up at night for urination, which was not a problem a few days before. He is an otherwise healthy man with no known medical condition. Physical examination of the man is normal. Important findings in laboratory evaluation are as follows:

Urine osmolality          175 mOsmol/kg H2O

Urine specific gravity  1.002

Serum osmolality        290 mOsmol/kg H2O

The man was advised to undergo water deprivation test, which confirmed that urine osmolality remained less than 300 mOsmol/kg H2O and it did not improve after administration of antidiuretic hormone.  After appropriate laboratory evaluation, the physician confirms that the man’s condition is due to an electrolyte abnormality. Which of the following electrolyte abnormalities is known to cause the condition the man is suffering from? Access full Qbank at https://ArcherReview.com – 30 day free trial. 

A. Hypokalemia

B. Hypochloremia

C. Hypocalcemia

D. Hypomagnesemia

E. Hyponatremia

USMLE Step 1 – Question of the Week#1

Q1. A 27-year-old man presents to physician with complain of pain in left thigh for last one month. Physical examination shows presence of a painful swelling just above left knee joint. Radiogram of left leg shows a radio-lucent lesion which is located eccentrically near lower end of femur. The lesion is surrounded by a thin rim of bone and soap-bubble appearance is present.

STEP1PIC2

After necessary evaluation, en bloc resection of the lesion is performed and is sent for microscopic examination. Histology of the lesion shows multi-nuclear giant cells in network of sheets of oval mononuclear cells. Necrosis and mitotic activity are present in the lesion and reactive bone is present at the periphery.

Which of the following mechanisms best describe pathogenesis of the bone lesion?

A. Dysregulation of RANKL-RANK signaling cascade

B. Increased production of 2-hydroxyglutarate

C. Defective diffusion of Indian hedgehog factor

D. Inactivating mutation of a tumor suppressor gene

E. Activation of Gs protein and increased production of cyclic adenosine monophosphate (cAMP)