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NBME 20 Answers

nbme20/Block 4/Question#46

A 28-year-old woman at 32 weeks' gestation comes to ...

Obstructive uropathy

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 +10  upvote downvote
submitted by xxabi(131),

Also for those of you who are totally clueless like me, urinary tract obstruction = obstructive uropathy.

 +6  upvote downvote
submitted by banieb(6),

During the last half of pregnancy dilation of the upper urinary tract can occur due to compression of the ureters by the growing fetus/uterus and the linea terminalis. The compression of these is not allowing fluid passage into the bladder causing urine buildup in the kidney, this leads to dilation of the kidney that ends up causing symptomatic hydronephrosis. this can end up in infection and symptoms such as the ones present in this patient like back pain and CVA tenderness. the crying is mainly due to the pain caused by the obstruction. and just as something extra: double pigtail catheters is a safe and simple way of treating symptomatic hydronephrosis of pregnancy.

banieb  Ureteral obstruction by the pregnant uterus https://www.ncbi.nlm.nih.gov/pubmed/1579937 +  


Distention/dilation of renal pelvis and calyces A . Usually caused by urinary tract obstruction (eg, renal stones, severe BPH, congenital obstructions, cervical cancer, injury to ureter, pregnancy apparently); other causes include retroperitoneal fibrosis, vesicoureteral reflux. Dilation occurs proximal to site of pathology. Serum creatinine becomes elevated if obstruction is bilateral or if patient has an obstructed solitary kidney. Leads to compression and possible atrophy of renal cortex and medulla.

 +1  upvote downvote
submitted by ye2019(1),

Physical exams showed tenderness of costophrenic angles, which are the places where the diaphragm (-phrenic) meets the ribs (costo-). Not the Costovertebral angle tenderness that we think to hint renal disease.I got confused with this point.

adong  honestly think this was a typo. hot trash +  
neovanilla  Assuming it was not a typo, how would the costophrenic angles be tender in this condition? ...From crying...? +  

 +0  upvote downvote
submitted by redvelvet(11),

costophrenic angle tenderness and fever WBC casts in tubules on that photo for example All of them is leading us to pyelonephritis. And even minor cystitis can cause pyelonephritis in pregnancy due to obstructive uropathy.

diegolc26  I thought it could be D or E at first. But the picture is really clear. There is inflammation within the tubules, not in the interstitium, that points more for Obstructive Uropathy which is also painful, can cause fever, and a risk factor could be compression due to elarged uterus. +  

 +0  upvote downvote
submitted by neonem(319),

Obstructive uropathy causes a postrenal azotemia --> when prolonged, tubular damage ensues. This leads to an acute tubular necrosis, characterized by necrotic plugs in the tubular system as seen in the image

meningitis  Does anyone know the relevance of the stem saying: "during this time she also has been crying frequently"? +8  
usmleuser007  Think the postrenal azotemia is d/t her pregnancy. With the increasing in size fetus, the pelvic cavity is being compressed and thus there is pressure on the ureters. This leading to the presentation. As per above --- the crying maybe just d/t her pain and emotional stress caused by worrying about possible complications regarding her fetus. +2  
maxillarythirdmolar  My gut tells me it must be some sort of transient change in placental size with hormonal changes. It's reminiscent of what you might expect for breast changes during the menstrual cycle, imo +  

pregnancy is a risk factor for acute pyelonephritis FA 2019 pg 589

Maybe all symptoms are related to hypercalcemia ("stones, bones, abdominal groans, thrones and psychiatric overtones") via PTHrP

The Role of PTHrP in Regulating Mineral Metabolism During Pregnancy - https://link.springer.com/article/10.1007/s12018-014-9157-6

 -1  upvote downvote
submitted by laminin(8),

also maybe could do process of elimination...the 'costophrenic angle tenderness' clues us in to it being a renal problem, and the only renal answer choice is obstructive uropathy

spdrwmn  glomerulonephritis was an answer choice +