This week, we are sharing another USMLE® Step 1-style practice question to test your knowledge of medical topics. Today’s case involves a 28-year-old man who was diagnosed with with fever, generalized muscle aches, and inguinal ulcers. Three months ago, he was diagnosed with acute urethritis and treated with a course of oral antibiotics. Which of the following is the most likely organism responsible for this patient’s symptoms? Can you figure it out?
A 28-year-old man comes to a primary care clinic with fever, generalized muscle aches, and inguinal ulcers. Three months ago, he was diagnosed with acute urethritis and treated with a course of oral antibiotics. He is sexually active and began a monogamous relationship with a new partner three months ago. They use condoms inconsistently. Temperature is 37.0°C (98.6°F), pulse is 90/min, respirations are 20/min, and blood pressure is 120/75 mmHg. The abdomen is soft and nontender. External genital examination reveals multiple purulent, tender ulcers on the penile shaft. Tender inguinal lymphadenopathy is noted along with overlying ulcerative lesions. Histological analysis of one of these ulcers reveals an organism organized in parallel strands. Which of the following is the most likely organism responsible for this patient’s symptoms?
A. Herpes simplex virus-2B. Klebsiella granulomatis
C. Treponema pallidum
D. Haemophilus ducreyi
E. Chlamydia trachomatis
Scroll down to find the answer!
The correct answer to today’s USMLE® Step 1 Question is…
D. Haemophilus ducreyi
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…
A. Herpes simplex virus-2
Incorrect: The clinical presentation of genital herpes includes multiple, shallow, tender vesicular genital ulcers. Histology of vesicular fluid typically shows multinucleated cells with intracytoplasmic inclusion bodies. This patient’s presentation is more consistent with chancroid, which is caused by Haemophilus ducreyi.
B. Klebsiella granulomatis
Incorrect: Donovanosis is caused by Klebsiella granulomatis, a gram-negative rod-shaped bacterium. Clinically, infection with this organism results in the presence of painless, ulcerative genital lesions without associated lymphadenopathy. This patient has painful genital lesions with lymphadenopathy, which is more consistent with chancroid, caused by Haemophilus ducreyi.
C. Treponema pallidum
Incorrect: The classic clinical presentation of primary syphilis is a single, painless, indurated genital ulcer. This patient has multiple painful genital ulcers with lymphadenopathy, which is more consistent with chancroid, caused by Haemophilus ducreyi.
E. Chlamydia trachomatis
Incorrect: Serotypes L1-L3 of Chlamydia trachomatis are responsible for developing lymphogranuloma venereum. This clinical entity presents with multiple, painless genital ulcers with painful lymphadenopathy. Histologically, this disease is characterized by the presence of epithelial cells with intracytoplasmic inclusion bodies. This patient has multiple painful genital ulcers with lymphadenopathy, which is more consistent with chancroid, caused by Haemophilus ducreyi.
Main Explanation
This patient presents with multiple painful genital ulcers and tender lymphadenopathy. Microscopic analysis indicates the presence of organisms organized in parallel strands (or a “school of fish” appearance). This description and clinical features are characteristic of Haemophilus ducreyi, the causative agent of the sexually transmitted infection chancroid.
Haemophilus ducreyi is a gram-negative rod transmitted through sexual contact, and clinical manifestations of the infection include multiple painful genital ulcers with a gray exudate and tender regional inguinal lymphadenopathy. One way to remember these clinical findings is that patients “do cry” when infected with H. ducreyi. Most lesions involve the penile shaft, prepuce, and glans penis in individuals with male genitalia. In individuals with female genitalia, the areas involved include the labia majora and minora, vaginal introitus, and the perianal regions. Diagnostic evaluation via gram stain will reveal gram-negative rods organized in parallel strands.
Genital ulcers in sexually active individuals raise concern for infection from several organisms, which requires prompt identification and treatment. Recalling the nature of the ulcer (painful vs. painless, multiple vs. single) and features of lymphadenopathy can assist in diagnosis, as outlined in the table below.
Major Takeaway
Chancroid is a sexually transmitted infection caused by the gram-negative rod Haemophilus ducreyi which causes multiple painful genital ulcers and tender inguinal lymphadenopathy. Under gram stain analysis, the organism appears as gram-negative rods in parallel strands or a “school of fish” appearance.
References
Lewis DA. Epidemiology, clinical features, diagnosis and treatment of Haemophilus ducreyi – a disappearing pathogen? Expert Rev Anti Infect Ther. 2014 Jun;12(6):687-96. doi: 10.1586/14787210.2014.892414. Epub 2014 Mar 6. PMID: 24597521.
DiCarlo RP, Martin DH. The clinical diagnosis of genital ulcer disease in men. Clin Infect Dis. 1997 Aug;25(2):292-8. doi: 10.1086/514548. PMID: 9332527.
Lewis DA. Diagnostic tests for chancroid. Sex Transm Infect. 2000 Apr;76(2):137-41. doi: 10.1136/sti.76.2.137. PMID: 10858718; PMCID: PMC1758295. _________________________
Want more USMLE® Step 1 practice questions? Try Osmosis today! Access your free trial and find out why millions of current and future clinicians and caregivers love learning with us.
The United States Medical Licensing Examination (USMLE®) is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). Osmosis is not affiliated with NBME nor FSMB.
Leave a Reply