What are the primary differential diagnoses for a patient presenting with symptoms of a vulvovaginal yeast infection?

Differential Diagnoses for Vulvovaginal Yeast Infection

The primary differential diagnoses for vulvovaginal yeast infection are bacterial vaginosis and trichomoniasis, as these three conditions account for the vast majority of vaginitis cases and share overlapping symptoms that cannot be reliably distinguished by symptoms alone. 1

Key Differential Diagnoses

Bacterial Vaginosis (BV)

• BV is diagnosed when three of four Amsel criteria are present: homogeneous white non-inflammatory discharge adhering to vaginal walls, clue cells on microscopy, vaginal pH >4.5, and fishy odor before or after 10% KOH application (whiff test). 2
• Clue cells are the hallmark finding: vaginal epithelial cells with bacteria adhered to their surface creating a stippled appearance with obscured borders on saline wet mount. 2
• BV presents with thin, white discharge and musty or fishy vaginal odor, contrasting with the thick white "cottage cheese" discharge of candidiasis. 3
• Critical distinction: BV has elevated vaginal pH (>4.5) while VVC maintains normal pH (≤4.5). 1

Trichomoniasis

• Caused by the protozoan Trichomonas vaginalis, presenting with profuse yellow-green discharge and vaginal/vulvar irritation. 3
• Wet mount sensitivity is only 40-80%, making nucleic acid amplification testing (NAAT) the preferred diagnostic method. 2
• Microscopic detection of motile trichomonads on wet preparation is the most commonly used but least sensitive method. 4
• Like BV, trichomoniasis typically has elevated vaginal pH (>4.5). 4

Diagnostic Approach to Differentiate

Clinical Features Comparison

• VVC symptoms: Pruritus (most prominent), thick white discharge, vulvar burning, dyspareunia, external dysuria, normal pH (≤4.5). 1
• BV symptoms: Fishy odor, thin homogeneous discharge, minimal irritation, pH >4.5, clue cells present. 2, 4
• Trichomoniasis symptoms: Profuse yellow-green discharge, significant irritation, pH >4.5, motile organisms on wet mount. 3, 4

Laboratory Differentiation

• For VVC: Wet preparation or Gram stain showing yeasts or pseudohyphae, or positive culture for yeast species. 1
• For BV: Quantitative Gram stain (Nugent criteria) is the most specific procedure when wet mount is equivocal, showing replacement of lactobacilli by mixed anaerobic flora. 2
• For trichomoniasis: NAAT testing is superior to wet mount due to higher sensitivity. 2

Critical Clinical Pitfalls

Multiple Concurrent Infections

• VVC can occur concomitantly with sexually transmitted diseases, requiring evaluation for all three common causes of vaginitis. 1
• It is not uncommon for women to have more than one microbial source for vaginal symptoms simultaneously. 4
• A comprehensive vaginal examination should include appropriate tests for detection of all three agents (Candida, BV, Trichomonas). 4

Diagnostic Errors to Avoid

• Never diagnose BV without clue cells unless confirmed by Gram stain, as this leads to treating the wrong condition. 2
• Do not rely solely on symptoms or physical examination, as vaginitis cannot be adequately diagnosed without laboratory methods. 4
• Avoid treating asymptomatic patients with incidental bacterial findings and no clue cells. 2

Special Considerations

• Approximately 10-20% of asymptomatic women harbor Candida species in the vagina, so identifying Candida by culture without symptoms should not lead to treatment. 1
• Laboratory testing fails to identify the cause of vaginitis in a substantial minority of women, highlighting the importance of thorough microscopic examination. 2
• VVC frequently follows antibacterial vaginal or systemic therapy, which can precipitate infection in women with asymptomatic Candida colonization. 1