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NBME 18 Answers

nbme18/Block 2/Question#17

65 yo woman, 1 week of swollen, painful knee

Uric acid

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submitted by i-de-liver(0),

Does anyone know why this is Uric Acid not N. gonorrhea? All I see in the micrograph are neutrophils. Is that white line in the middle of the picture that overlays the lymphocyte supposed to be the needle-shaped uric acid? Or is it because she's an old lady and usually septic Arthritis is from S. Aureus, so it would more like by uric acid and not gonorrhea since she's older?

maverick95  I struggled between those two answer choices as well. I thought that the large needle shape right in the middle was a uric acid crystal which helped push me towards Uric Acid as my answer. I also took into account that she was older (even though STIs are rampant among the elderly) she didn't really seem to have any other symptoms or history of STI/gonorrhea. I figured with her age that she just wasn't able to excrete Uric Acid enough, and got a gout. Something a pathologist told me one time was that they put the focus of the picture in the middle of the shot. So considering the uric acid-looking shape was right in the middle, I figured that's what they wanted us to focus on with the picture. Hope this helps. +  
i-de-liver  Ah gotcha! I guess I shouldn't have thought that the thing in the middle was an artifact lol... thank you!! +  
a1913  I believe it's because: 1) there is nothing given that would be risk factors for this woman to have N. gonorrhea 2) The thing in the middle is indeed an MSU crystal, just not under polarized light 3) apparently we get acute inflammation and increase in WBCs with crystal-induced arthropathies, per Table 11-2 on page 8 here (10 page document, top of page of interest will say p. 260) --> Also take a look at the pics on the previous page, left column for an example. I got this wrong as well, but I definitely won't again! lol +