In a 35-year-old woman with green‑yellow purulent vaginal discharge that began after menstruation, multifocal rounded erythematous macules on the vaginal mucosa, and pelvic tenderness, which is the most likely diagnosis: vaginal candidiasis, bacterial vaginosis, atrophic vaginitis, or vaginal trichomoniasis?

Vaginal Trichomoniasis

The most likely diagnosis is vaginal trichomoniasis (Option D), based on the classic triad of greenish-yellow purulent discharge, multifocal rounded erythematous macules on the vaginal mucosa (strawberry cervix), and pelvic tenderness in a reproductive-age woman. 1

Diagnostic Reasoning

Key Clinical Features Supporting Trichomoniasis

• The greenish-yellow purulent discharge is pathognomonic for Trichomonas vaginalis infection, as the CDC defines this as the hallmark presentation of trichomoniasis—a diffuse, malodorous, yellow-green discharge with vulvar irritation. 1

• The multifocal rounded macular erythematous lesions represent the classic "strawberry cervix" (punctate red lesions on the vaginal mucosa), which is a highly specific finding for trichomoniasis on speculum examination. 1

• Pelvic tenderness indicates ascending infection, which is consistent with trichomoniasis as a sexually transmitted infection that can cause upper genital tract inflammation. 1

• The timing after menstruation is significant, as menstrual blood raises vaginal pH and can trigger symptomatic trichomoniasis in previously asymptomatic carriers. 2

Why Other Options Are Excluded

Vaginal candidiasis (Option A) is ruled out because:

• Candidiasis presents with thick, white "cottage cheese-like" discharge, not greenish-yellow purulent discharge 1, 3
• Candidiasis causes intense vulvar pruritus and maintains normal vaginal pH (3.8-4.2), not the elevated pH expected with purulent discharge 4, 3
• The strawberry cervix finding is not seen in candidiasis 1

Bacterial vaginosis (Option B) is excluded because:

• BV produces a thin, homogeneous white or gray discharge, not greenish-yellow purulent discharge 4, 5
• BV is characterized by a fishy odor (positive whiff test) and clue cells, not erythematous macules 4, 6
• BV is a noninflammatory condition without the punctate hemorrhagic lesions seen here 3

Atrophic vaginitis (Option C) is inappropriate because:

• This occurs in postmenopausal women due to estrogen deficiency, not in a 35-year-old reproductive-age woman 2, 6
• Atrophic vaginitis presents with vaginal dryness, dyspareunia, and minimal discharge, not purulent discharge 6

Diagnostic Confirmation

• Wet-mount microscopy should reveal motile flagellated trichomonads, though this test has only 50-75% sensitivity and may miss 30-50% of infections. 1, 3

• Nucleic acid amplification testing (NAAT) for Trichomonas vaginalis is recommended by the CDC due to superior sensitivity compared to wet mount microscopy. 5, 7

• Vaginal pH will be elevated (>4.5), distinguishing trichomoniasis from candidiasis. 2, 6

Treatment Algorithm

• Administer metronidazole 2 g orally as a single dose to the patient for microbiologic cure. 4, 1

• Treat all sexual partners simultaneously with the same metronidazole 2 g single-dose regimen to prevent reinfection, as treatment failure is usually due to untreated partners. 1, 5, 3

• Instruct the patient to abstain from sexual intercourse until both she and her partner have completed therapy and are asymptomatic. 4, 1

Critical Clinical Considerations

• Trichomoniasis increases HIV acquisition and transmission risk, making partner treatment and safe sex counseling essential. 1

• Screen for concurrent sexually transmitted infections (Chlamydia trachomatis and Neisseria gonorrhoeae) using NAAT, as STIs frequently coexist. 5, 7

• In pregnancy, trichomoniasis is associated with preterm delivery and premature rupture of membranes, though treatment with metronidazole 2 g single dose is safe and recommended. 4, 1