A 24-year-old man presents with a painless genital ulcer for the past 2 weeks. He reports that he recently has been having unprotected sex with multiple partners. Past medical history is unremarkable. On physical examination, a single ulcer is present on the dorsal shaft of the penis which is circumscribed, indurated, and partially healed. There is moderate inguinal lymphadenopathy but no buboes. Which of the following tests would confirm the most likely diagnosis in this patient?

Perform a darkfield microscopic examination of a swab from the chancre

Swab the chancre and perform a saline wet mount

Fluorescent treponemal antibody absorption (FTA-ABS) test

Venereal Disease Research Laboratory (VDRL) test

A 28-year-old woman comes to the emergency department for a rash that began 3 days ago. She has low-grade fever and muscle aches. She has no history of serious illness and takes no medications. She has had 5 male sexual partners over the past year and uses condoms inconsistently. Her temperature is 38.1°C (100.6° F), pulse is 85/min, and blood pressure is 126/89 mm Hg. Examination shows a diffuse maculopapular rash that includes the palms and soles. The remainder of the examination shows no abnormalities. A venereal disease research laboratory (VDRL) test is positive. Which of the following is the next appropriate step in management?

Fluorescent treponemal antibody absorption test

An endocervical swab is performed and nucleic acid amplification testing via polymerase chain reaction is conducted. It is positive for Chlamydia trachomatis and negative for Neisseria gonorrhoeae. Which of the following is the most appropriate pharmacotherapy?

Intramuscular ceftriaxone plus oral azithromycin

Intravenous cefoxitin plus oral doxycycline

Sexually transmitted infections for USMLE Step 2 CK: High-Yield Internal Medicine Lessons

Syphilis - The Great Pretender

Organism: Treponema pallidum (spirochete).
Transmission: Sexual contact, vertical.

Darkfield microscopy of Treponema pallidum

Diagnosis:
- Screen: VDRL, RPR.
- Confirm: FTA-ABS, TP-PA.
Treatment: Penicillin G (IM/IV).

⭐ Jarisch-Herxheimer reaction: Acute, self-limited febrile reaction within 24 hours of antibiotic therapy, due to massive cytokine release from dying spirochetes. Not an allergic reaction.

Gonorrhea & Chlamydia - The Urethritis Duo

Organisms: Neisseria gonorrhoeae (Gram-negative diplococcus) vs. Chlamydia trachomatis (obligate intracellular).
Presentation: Often asymptomatic. Men: urethritis (purulent vs. watery discharge). Women: cervicitis, PID.
Diagnosis: NAAT (Nucleic Acid Amplification Test) is the gold standard for both.
- Gram stain: Shows intracellular diplococci in gonorrhea.

Treatment: Co-infection is common; treat both.
- Ceftriaxone for Gonorrhea.
- Doxycycline (or Azithromycin) for Chlamydia.
Complications: PID, infertility, ectopic pregnancy. Disseminated gonococcal infection (arthritis, dermatitis). Chlamydia can cause reactive arthritis.

⭐ Fitz-Hugh-Curtis Syndrome: Perihepatitis (violin-string adhesions) seen in women with PID caused by either organism.

Genital Ulcer Diseases - Painful Decisions

📌 Mnemonic: Herpes & Haemophilus are Hurtful (Painful).

Condition	Organism	Ulcer Characteristics
Herpes	HSV-1/2	Multiple, painful vesicles on erythematous base
Chancroid	H. ducreyi	Single, painful, purulent, ragged edges
Syphilis	T. pallidum	Single, painless, indurated, clean base

⭐ Co-infection with HIV is common in patients with genital ulcers, especially syphilis and chancroid. The ulcer serves as a portal of entry for HIV.

HPV & Trichomonas - Warts & Protozoa

Human Papillomavirus (HPV): DNA virus; causes warts (condylomata acuminata) & dysplasia.
- High-risk: Types 16, 18 → Cervical, penile, anal, oropharyngeal SCC.
- Low-risk: Types 6, 11 → Anogenital warts.
- Dx: Pap smear shows koilocytes (perinuclear halos).
- Rx: Podophyllin, cryotherapy, imiquimod. Prevention via Gardasil-9 vaccine.
Trichomonas vaginalis: Motile protozoan.
- Presentation: Frothy, yellow-green, foul-smelling discharge.
- Dx: Saline wet mount shows motile trophozoites.
- Rx: Metronidazole for patient AND partner.

⭐ Exam Favorite: A "strawberry cervix" (colpitis macularis) is pathognomonic for Trichomoniasis.

Koilocytes vs. Trichomonas on Pap Smear

High‑Yield Points - ⚡ Biggest Takeaways

Chlamydia is the most common bacterial STI, often asymptomatic, and can lead to Pelvic Inflammatory Disease (PID).

Gonorrhea can cause purulent arthritis in sexually active young adults; treat with ceftriaxone.

Syphilis (Treponema pallidum) is diagnosed with RPR and confirmed with FTA-ABS; penicillin G is the universal treatment.

A painless genital ulcer suggests primary syphilis, whereas painful vesicles point towards Herpes (HSV).

PID classically presents with cervical motion tenderness (Chandelier sign).

Trichomonas features a strawberry cervix and motile organisms on wet mount; treat patient and partner with metronidazole.

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