Q&A Medicine>>>>>Nephrology
Question 35#

A 28-year-old woman with Crohn disease presents to the Emergency Department with back pain that started last night. She describes a colicky pain that is located on the right side of her back and shoots down to her groin. The pain is also associated with nausea and vomiting. Her temperature is 37.3°C, blood pressure is 128/84 mmHg, heart rate is 98 beats per minute, and respiratory rate is 18 breaths per minute. The patient appears uncomfortable and has some right flank pain on palpation. A pelvic examination is performed and shows no cervical discharge or cervical motion tenderness. Her laboratory values show a normal hemoglobin and leukocyte count, a urine pregnancy test is negative, and a urine dipstick shows 2+ blood but is negative for nitrites or leukocyte esterase.

What is the most likely diagnosis?

A. Pyelonephritis
B. Nephrolithiasis
C. Appendicitis
D. Ectopic pregnancy

Correct Answer is B

Comment:

Nephrolithiasis. This patient is presenting with the typical symptoms of a kidney stone. Patients with Crohn disease are at risk of developing calcium oxalate stones due to increased absorption of oxalate in the GI tract (and therefore increased oxaluria), which has two causes. First, malabsorption of bile salts and GI tract inflammation increase mucosal permeability. Second, fatty acids (also a result of malabsorption) bind intestinal calcium, and so less calcium is available to bind and trap intestinal oxalate. This causes an increase in free oxalate that can be absorbed, eventually making it back to the kidneys to be excreted.

Calcium stones are the most common type of kidney stones, and patients with these stones are encouraged to increase their dietary intake of calcium (in order to decrease oxalate absorption in the GI tract). Thiazide diuretics may also be beneficial since they increase calcium reabsorption and therefore decrease urine calcium. Ammonium magnesium phosphate (struvite) stones are caused by urinary tract infections with urease-positive organisms (e.g., Proteus, Klebsiella) and can form staghorn calculi. Uric acid stones are associated with hyperuricemia (e.g., leukemia, gout). Cystine stones are seen in the genetic disease cystinuria and are treated by alkalinizing the urine with acetazolamide.

(A) Pyelonephritis would also produce flank pain, but unlike nephrolithiasis it would also produce fever, leukocytosis, and a urine dipstick showing infection (e.g., positive nitrites, positive leukocyte esterase). (C) Appendicitis is important to consider in any young patient with abdominal pain; however, it would be unusual for appendicitis to cause hematuria. (D) Ectopic pregnancies can mimic the pain of a kidney stone; however, this diagnosis is unlikely given the negative pregnancy test.