Causes of Bilateral Inguinal Lymphadenopathy in Young Reproductive-Age Women

1. Sexually transmitted infections (most common cause overall)

• Primary syphilis (Treponema pallidum) - Regional inguinal lymphadenopathy accompanies the chancre within about a week of the lesion appearing. Nodes are firm, non-suppurative, and painless, and involvement is classically bilateral - Harrison's Principles of Internal Medicine, 22E.
• Genital herpes (HSV-1/2) - Primary infection causes painful, punched-out vulvar/perineal ulcers with tender, painful inguinal lymphadenopathy that is usually bilateral and accompanied by fever, headache, and malaise - Harrison's Principles of Internal Medicine; Tintinalli's Emergency Medicine.
• Lymphogranuloma venereum (LGV, Chlamydia trachomatis L1-L3) - Produces firm, matted, "heaped-up" inguinal/femoral nodes; when nodes above and below the inguinal ligament are both involved this gives the "groove sign," and involvement is often bilateral, described as "bilateral, firm, immovable masses above the Poupart ligament" - Fitzpatrick's Dermatology; Robbins & Kumar Basic Pathology. LGV is also an increasing cause of proctocolitis in women who have receptive anal intercourse.
• Chancroid (Haemophilus ducreyi) - Painful ulcer with tender, suppurative inguinal adenopathy ("bubo") - classically unilateral, though bilateral cases occur - Washington Manual of Medical Therapeutics; Rosen's Emergency Medicine.
• Granuloma inguinale / Donovanosis (Klebsiella granulomatis) - True lymphadenopathy is uncommon; presents more with subcutaneous "pseudobuboes" - Smith and Tanagho's General Urology.
• HIV (acute seroconversion) - Generalized lymphadenopathy that can include inguinal nodes.

2. Local/regional skin and soft-tissue infections

• Vulvar or perineal cellulitis, folliculitis, or infected insect/shaving-related lesions
• Tinea cruris, scabies, pubic lice (bilateral groin involvement is typical since the whole groin/vulvar skin is exposed)
• Lower-extremity infections (bilateral cellulitis, infected insect bites, or dermatophyte infections of both feet/legs) draining to bilateral inguinal nodes
• Bartholin gland abscess/infection

3. Systemic infections causing generalized (including bilateral inguinal) lymphadenopathy

• Epstein-Barr virus (infectious mononucleosis) - classically involves bilateral posterior cervical, axillary, and inguinal nodes - Peripheral Lymphadenopathy: Approach and Diagnostic Tools, PMC.
• Cytomegalovirus, toxoplasmosis, acute HIV
• Tuberculosis (regional nodal TB, endemic areas)
• Filariasis (in endemic tropical regions - causes inguinal lymphadenopathy/lymphedema) - Fitzpatrick's Dermatology.

4. Malignant causes (less common at this age but must be excluded)

• Vulvar, vaginal, or anal squamous cell carcinoma metastasizing to inguinal nodes (rare in young women, but vulvar intraepithelial neoplasia/HPV-related lesions can occur in reproductive-age women)
• Lymphoma (Hodgkin or non-Hodgkin) - inguinal presentation alone is uncommon, but bilateral involvement can occur as part of more widespread disease - Peripheral Lymphadenopathy: Approach and Diagnostic Tools.
• Melanoma of the lower limb/vulva

5. Autoimmune / miscellaneous

• Sarcoidosis, SLE, and other connective tissue diseases (uncommon presentation site but part of the MIAMI framework - Malignancy, Infection, Autoimmune, Miscellaneous, Iatrogenic)
• Reactive, benign, self-limited lymphadenopathy - inguinal nodes up to 1-2 cm are a normal finding in many healthy young adults, especially those who walk barefoot; this is more prominent in the inguinal region than any other nodal basin - AAFP, "Unexplained Lymphadenopathy."

Practical diagnostic approach

1. History: sexual history and partner symptoms, genital ulcer or discharge, dysuria, fever/systemic symptoms, pruritus/rash, recent shaving or skin trauma, travel/exposure history, B-symptoms (fever, weight loss, night sweats).
2. Examination: inspect vulva, vagina, and perineum for ulcers (painful vs painless), vesicles, discharge; characterize nodes (size, tenderness, consistency, fixation, fluctuance/bubo); examine lower limbs for cellulitis or dermatophyte infection; check for hepatosplenomegaly or other lymph node groups (generalized lymphadenopathy points away from a purely local STI cause).
3. Work-up: syphilis serology (RPR/VDRL + treponemal test), HSV PCR/culture of any ulcer, chlamydia/LGV NAAT, HIV testing, dark ulcer exudate for H. ducreyi if suspected, CBC with peripheral smear/monospot if systemic features, and consider excisional biopsy if nodes are firm, matted, non-tender, enlarging, or persist beyond 4-6 weeks despite treatment (to exclude lymphoma or metastatic carcinoma).

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