Step 1 topics → Reproductive → Chancroid and Granuloma Inguinale

Chancroid and Granuloma Inguinale

USMLE Step 1 trap: Confuses the painful chancroid ulcer with the painless syphilitic chancre. Chancroid (Haemophilus ducreyi) causes a painful, soft, purulent ulcer with ragged edges, in contrast to the painless, indurated chancre of syphilis.

Chancroid and granuloma inguinale are two STIs that show up on USMLE Step 1 primarily as contrast questions — the exam wants you to distinguish them from each other and from syphilis based on ulcer characteristics and pathologic findings. Chancroid is caused by Haemophilus ducreyi and produces a painful, soft, purulent genital ulcer. Granuloma inguinale is caused by Klebsiella granulomatis and is identified by its pathognomonic finding: Donovan bodies seen within macrophages on biopsy. Neither of these is high-yield on its own, but both appear in vignettes where the key move is differentiating ulcer types.

The main trap is the word 'chancroid' itself — students hear 'chancre' and assume painless. That's syphilis. Chancroid is the painful one. This distinction is the single most tested fact about chancroid on USMLE Step 1. For granuloma inguinale, the confusion usually involves Donovan bodies — students sometimes attribute them to Chlamydia trachomatis (which causes LGV), but Donovan bodies are specific to K. granulomatis infection, found inside macrophages on tissue biopsy.

The exam will typically present a clinical vignette with ulcer characteristics and ask you to identify the organism or the diagnostic finding. You won't be asked to memorize dosing regimens in depth, but knowing that azithromycin or ceftriaxone treats chancroid is fair game. The conceptual work here is building a clean mental map of ulcer STIs: painless and indurated = syphilis; painful with ragged edges = chancroid; beefy red ulcer with Donovan bodies in macrophages = granuloma inguinale.

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Common misconceptions

Common mistake
Wrong: The ulcer of chancroid is painless like the syphilitic chancre.
Right: Chancroid (Haemophilus ducreyi) causes a painful, soft, purulent ulcer with ragged edges, in contrast to the painless, indurated chancre of syphilis.
The name 'chancroid' sounds like 'chancre,' which is the painless syphilitic ulcer — that's exactly why students mix these up. But chancroid (H. ducreyi) causes a painful, soft, ragged-edged, purulent ulcer; the 'soft' descriptor is key and sometimes used as the distinguishing adjective in vignettes. Syphilis gives you a hard (indurated), painless ulcer. When you see 'painful genital ulcer,' think chancroid first.
Common mistake
Wrong: Donovan bodies are the inclusion bodies seen in Chlamydia trachomatis infection.
Right: Donovan bodies are intracellular rod-shaped organisms seen within macrophages on biopsy of granuloma inguinale (caused by Klebsiella granulomatis), not Chlamydia.
Donovan bodies are not related to Chlamydia — they are intracytoplasmic inclusions of Klebsiella granulomatis found inside macrophages on biopsy of granuloma inguinale lesions. Chlamydia trachomatis (serovars L1–L3) causes lymphogranuloma venereum, which has its own finding of tender inguinal lymphadenopathy (buboes), not Donovan bodies. Keep these two diseases separated: K. granulomatis = beefy red ulcer + Donovan bodies in macrophages; Chlamydia LGV = painful nodes, no Donovan bodies.
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What the exam tests

  1. Given a vignette describing a painful, soft, purulent genital ulcer with ragged edges, identify the causative organism (H. ducreyi) and distinguish it from the painless indurated chancre of syphilis.
  2. Recognize granuloma inguinale by its biopsy finding of Donovan bodies — intracellular rod-shaped organisms within macrophages — and correctly attribute this to Klebsiella granulomatis, not Chlamydia.

Can you avoid these mistakes?

A 28-year-old man presents with a painful genital ulcer with ragged, undermined edges and a purulent base. On exam the ulcer is soft. What is the causative organism, and how does this presentation differ from syphilitic chancre?
A biopsy of a genital ulcer shows large macrophages containing intracellular rod-shaped organisms. What is this finding called, what organism causes it, and what disease does this confirm?
A student says 'both chancroid and syphilis cause painless ulcers.' What is wrong with this statement, and what feature most reliably distinguishes the two ulcers clinically?
A vignette mentions Donovan bodies. Another student attributes this to Chlamydia trachomatis LGV. What is the correct organism, and what would you expect to find on biopsy histologically?

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