What are the differential diagnoses, evaluation steps, and first‑line treatments for vaginal pain in a reproductive‑age woman?

Vaginal Pain: Differential Diagnosis, Evaluation, and First-Line Treatment

Immediate First Steps

Obtain serum or urine β-hCG immediately in all reproductive-age women presenting with vaginal or pelvic pain—failure to do so can result in missed ectopic pregnancy (which carries a positive likelihood ratio of 111 when an adnexal mass is present without intrauterine gestation) and inappropriate radiation exposure. 1, 2

Differential Diagnosis by Pain Location

Entry (Superficial) Vaginal Pain

• Vulvodynia/vulvar vestibulitis: Localized burning reproduced by cotton-swab touch to vestibule 3
• Atrophic vaginitis: Associated with hypoestrogenism, common in postmenopausal or breastfeeding women 4
• Infectious vaginitis: Bacterial vaginosis, candidiasis (Candida albicans vs. non-albicans species), or trichomoniasis 4, 5
• Vaginismus: Involuntary pelvic floor spasm noted during speculum or digital examination 3
• Inadequate lubrication: Often situational or hormonal 3

Deep Vaginal/Pelvic Pain

• Pelvic inflammatory disease (PID): Accounts for 20% of acute pelvic pain cases; requires immediate empiric antibiotics when minimum criteria met (uterine + adnexal + cervical motion tenderness) 1, 2
• Endometriosis: Primary cause of chronic/recurrent pelvic pain in reproductive-age women 2
• Ovarian pathology: Cysts (most common gynecologic cause of acute pain), torsion, tubo-ovarian abscess 1, 2
• Ectopic pregnancy: Must be excluded when β-hCG positive 6, 1
• Adenomyosis: Common cause of deep dyspareunia 2
• Urologic causes: Interstitial cystitis/painful bladder syndrome, urethral diverticulum, recurrent UTI 7, 8

Diagnostic Evaluation Algorithm

Step 1: Pregnancy Testing

• β-hCG positive: Proceed immediately to combined transvaginal AND transabdominal ultrasound to evaluate for intrauterine vs. ectopic pregnancy 9, 1, 2
• β-hCG negative: Proceed to Step 2 1, 2

Step 2: First-Line Imaging (β-hCG Negative)

Combined transvaginal and transabdominal ultrasound with Doppler is the first-line imaging modality for suspected gynecologic causes of vaginal/pelvic pain, demonstrating 93% sensitivity and 98% specificity for tubo-ovarian abscess and 78.4% overall sensitivity for common pathologies including ovarian torsion, endometriotic cysts, and hemorrhagic cysts. 9, 1, 2

• Transvaginal component: Provides superior spatial resolution (93% sensitivity for tubal involvement in PID) 9, 2
• Transabdominal component: Visualizes high-lying adnexa, free pelvic fluid, and overall pelvic architecture 9
• Doppler assessment: Essential for detecting ovarian torsion (abnormal/absent venous flow has 100% sensitivity and 97% specificity) 9

Step 3: Office-Based Tests for Vaginitis

When superficial pain or discharge is present:

• Vaginal pH: Normal <4.5; elevated in bacterial vaginosis (>4.5) and trichomoniasis 5
• Whiff test: Positive (fishy odor with KOH) in bacterial vaginosis 5
• Saline wet mount: Identifies clue cells (bacterial vaginosis), motile trichomonads, or white blood cells 5
• 10% KOH preparation: Reveals budding yeast or pseudohyphae (candidiasis) 5
• Yeast culture with speciation: Crucial for recurrent cases to differentiate C. albicans from non-albicans species 4

Step 4: Second-Line Imaging

If ultrasound is nondiagnostic or equivocal, proceed to CT abdomen and pelvis with IV contrast, which demonstrates 89% sensitivity versus 70% for ultrasound when the differential is broad and includes non-gynecologic pathology. 9, 1

For suspected endometriosis or adenomyosis based on clinical presentation, MRI pelvis (with and without contrast) is first-line, demonstrating approximately 90.3% sensitivity and 91% specificity for endometriosis detection. 2

First-Line Treatment by Diagnosis

Pelvic Inflammatory Disease

Initiate empiric broad-spectrum antibiotics immediately when minimum clinical criteria are met (uterine + adnexal + cervical motion tenderness)—do not wait for culture results, as delay causes permanent reproductive damage. 1

• Coverage must include: N. gonorrhoeae, C. trachomatis, gram-negative facultative bacteria, anaerobes, and streptococci 1
• Obtain cervical cultures for gonorrhea/chlamydia to guide partner treatment 1

Infectious Vaginitis

• Bacterial vaginosis: Metronidazole is primary treatment; maintenance therapy for recurrent cases 4, 5
• Candida albicans: Topical antifungal agents first-line; maintenance fluconazole for recurrent cases 4, 5
• Non-albicans Candida (especially C. glabrata): Vaginal boric acid 600mg daily for 14 days is effective first choice 4
• Trichomoniasis: Metronidazole; high-dose tinidazole for resistant cases 4, 5

Atrophic Vaginitis

• Vaginal estrogen therapy is first-line for hypoestrogenism-related pain 4

Ovarian Torsion

• Urgent surgical consultation when ultrasound shows enlarged ovary with decreased/absent Doppler flow 1

Ectopic Pregnancy

• Immediate obstetric consultation for methotrexate vs. surgical management 1

Critical Pitfalls to Avoid

• Never skip pregnancy testing, even if patient reports contraceptive use or recent menses—missed ectopic pregnancy is life-threatening 1, 2
• Do not require multiple criteria before treating PID—requiring two or more findings reduces sensitivity and misses cases that cause infertility 1
• Do not order transvaginal ultrasound alone—may miss high-lying adnexal pathology and free fluid critical to diagnosis 9
• Do not use CT as first-line for gynecologic causes—ultrasound has equivalent or superior accuracy without radiation 9, 1
• Do not assume gynecologic origin—15-25% of pelvic pain has gastrointestinal or urologic causes 2
• Do not overlook urologic causes (interstitial cystitis, urethral diverticulum) when bladder symptoms coexist with pain 7