Each week, Osmosis shares a USMLE® Step 1-style practice question to test your knowledge of medical topics. Today’s case focuses on a 26-year-old man with penile discharge and urination pain after engaging in unprotected sexual intercourse. Can you figure it out?
A 26-year-old man presents to his primary care physician with penile discharge. He also reports experiencing pain with urination starting 3 days ago. Last weekend, he engaged in unprotected sexual intercourse with a new female partner. His vital signs are 37 °C (98.6.°F), pulse is 67/min, respirations are 14/min, blood pressure is 126/74 mmHg, and oxygen saturation is 99% on room air. Physical examination shows mucoid discharge at the urethral meatus. Which of the following laboratory findings is most likely to be observed in this patient?
A. Positive leukocyte esterase with no bacteria
B. Positive leukocyte esterase and positive nitrite
C. High white blood cell count and hyaline casts
D. Urine pH 8.5
E. Red blood cells and positive leukocyte esterase
Scroll down to find the answer!
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The correct answer to today’s USMLE® Step 1 Question is…
A. Positive leukocyte esterase with no bacteria
Before we get to the Main Explanation, let’s look at the incorrect answer explanations. Skip to the bottom if you want to see the correct answer right away!
Incorrect answer explanations
The incorrect answers to today’s USMLE® Step 1 Question are…
B. Positive leukocyte esterase and positive nitrite
Incorrect: Positive leukocyte esterase and positive nitrite are more consistent with cystitis or pyelonephritis, which are most often caused by Escherichia coli. Urethritis is more commonly caused by Neisseria gonorrhea or Chlamydia trachomatis, which are non-nitrite producing organisms.
C. High white blood cell count and hyaline casts
Incorrect: A high white blood cell count is not usually seen with lower urinary tract infections but is more commonly seen in the setting of pyelonephritis. Hyaline casts may also be observed in pyelonephritis.
D. Urine pH 8.5
Incorrect: Alkaline urine is more commonly seen with infectious organisms such as Proteus mirabilis, a common culprit in patients with chronic pyelonephritis.
E. Red blood cells and positive leukocyte esterase
Incorrect: These urinalysis findings are more commonly found in the setting of nephrolithiasis, which presents with lancinating flank radiating to the groin, nausea, and vomiting.
Main Explanation
This young male patient, who is presenting with penile discharge and dysuria in the setting of recent unprotected sexual intercourse, likely has urethritis. Of the laboratory abnormalities listed, urinalysis with positive leukocyte esterase and no bacteria is most likely consistent with sterile pyuria.
Urethritis refers to inflammation of the urethra. Clinically, it is difficult to distinguish from cystitis (bladder inflammation), since it presents with many similar symptoms including dysuria or discharge at the urethral meatus. However, urethritis can be differentiated clinically from pyelonephritis, based on absence of systemic features including fever, tachycardia, costovertebral angle tenderness, nausea, and vomiting.Urethritis can be further differentiated from other urinary tract infections based on the causative organisms and laboratory findings. In general, the majority of urethral infections are caused by sexuallay transmitted organisms, such as Chlamydia trachomatis and Neisseria gonorrhoeae. A urinalysis will reveal sterile pyuria, which refers to positive leukocyte esterase without identifiable bacteria on microscopy. Confirmatory diagnosis relies on urethral swabs with subsequent nucleic acid amplification testing, in addition to possible Gram-staining for Neisseria gonorrhea.
Major Takeaway
Urethritis refers to inflammation of the urethra. It is commonly caused by sexuallly transmitted infections from Chlamydia trachomatis and Neisseria gonorrhoeae, and it demonstrates sterile pyuria in urinalysis.
References
Curry, M. (2017, May 18). Rosen’s Emergency Medicine: Concepts and Clinical Practice. Retrieved from https://www.us.elsevierhealth.com/rosens-emergency-medicine-concepts-and-clinical-practice-9780323354790.html. ISBN: 0323354793
Workowski KA, Bolan GA, Centers for Disease Control and Prevention. Sexually transmitted diseases treatment guidelines, 2015. MMWR Recomm Rep 2015; 64:1. doi: 10.15585/mmwr.rr6805a1
Taylor SN, Liesenfeld O, Lillis RA, et al. Evaluation of the Roche cobas® CT/NG test for detection of Chlamydia trachomatis and Neisseria gonorrhoeae in male urine. Sex Transm Dis 2012; 39:543. doi: 10.1097/OLQ.0b013e31824e26ff.
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