Top 15 Differential Diagnoses

These diagnoses span primary cyclic, secondary/structural, infectious, functional, and systemic etiologies — all capable of producing the described symptom cluster in this age group.

1. 🔴 Primary Dysmenorrhea

• Mechanism: Excess endometrial prostaglandins (PGE2, PGF2α) → exaggerated uterine contractions + myometrial ischemia
• Symptoms: Crampy lower abdominal pain beginning hours before or at onset of flow, lasting 48–72 hours; associated nausea, diarrhea, headache
• Key feature: Normal pelvic exam and pelvic ultrasound; pain has never started before the onset of menses; onset typically within 1–2 years of menarche
• Workup: Clinical diagnosis; urine βhCG negative; pelvic US normal
• Tx: NSAIDs (ibuprofen, naproxen), combined oral contraceptives, heat

Berek & Novak's Gynecology — The management of primary dysmenorrhea includes NSAIDs started at the onset of bleeding or cramping, and hormonal contraceptives that inhibit ovulation and decrease endometrial prostaglandin levels.

2. 🔴 Endometriosis

• Mechanism: Ectopic endometrial glands and stroma implant on ovaries, cul-de-sac, peritoneum, bowel; cyclical bleeding in ectopic sites → inflammation, adhesions, endometriomas
• Symptoms: Dysmenorrhea starting 1–2 weeks before menses and persisting after flow ends; dyspareunia; dyschezia; chronic pelvic pain; infertility
• Can cause: Endometriomas ("chocolate cysts") → severe ovarian cysts; heavy bleeding; dysmenorrhea
• Prevalence: ~10% of reproductive-age women; >30% of women with chronic pelvic pain
• Workup: Pelvic US (endometrioma: low-level internal echoes), MRI, definitive = diagnostic laparoscopy with biopsy
• Tx: NSAIDs, oral contraceptives, progestins, GnRH agonists/antagonists (elagolix, leuprolide), surgical excision

Berek & Novak's Gynecology — "The most common cause of secondary dysmenorrhea is endometriosis, followed by adenomyosis and nonhormonal intrauterine devices."

3. 🔴 Adenomyosis

• Mechanism: Endometrial glands and stroma invade the myometrium → uterus enlarges and bleeds heavily within its wall
• Symptoms: Progressive, severe dysmenorrhea; heavy, prolonged menstrual bleeding; diffusely enlarged, "boggy," tender uterus; uterine cramps
• Key feature: Typically described in older (>35) multiparous women but increasingly diagnosed in young nulliparous women; often coexists with endometriosis
• Workup: Transvaginal ultrasound (myometrial heterogeneity, asymmetric thickening), MRI (junctional zone >12 mm), definitive = hysterectomy pathology
• Tx: NSAIDs, LNG-IUD, GnRH agonists, combined OCP; surgery reserved for refractory cases

Harrison's Principles of Internal Medicine 22E — "Adenomyosis [is] a condition caused by the presence of endometrial glands within the myometrium, producing a diffusely enlarged, boggy uterus."

4. 🟠 Uterine Leiomyomas (Fibroids)

• Mechanism: Smooth muscle tumors distorting the uterine cavity (submucosal) or enlarging the uterus; increase uterine surface area and impair contractility → heavy bleeding; submucosal fibroids also cause dysmenorrhea
• Symptoms: Heavy menstrual bleeding, pelvic pressure, painful cramps, urinary frequency; submucosal = heaviest bleeding + worst dysmenorrhea
• Although uncommon at age 20, fibroids do occur in teenagers and young adults, particularly in those of African descent
• Workup: Pelvic US (hypoechoic solid masses), sonohysterography, hysteroscopy
• Tx: NSAIDs, tranexamic acid, GnRH agonists (pre-op), LNG-IUD; myomectomy for fertility preservation

Harrison's Principles — "Large fibroids can cause chronic pelvic pain or pressure, and submucosal fibroids may be associated with dysmenorrhea."

5. 🟠 Hemorrhagic Ovarian Cyst

• Mechanism: Failure of follicular rupture → follicular cyst continues enlarging; or corpus luteum fails to involute → hemorrhage into cyst wall causes acute pain
• Symptoms: Acute unilateral sharp pelvic pain, often in luteal phase or at mid-cycle; rupture can cause peritoneal signs; significant hemoperitoneum if large
• Types: Follicular cyst, corpus luteum cyst (most likely to cause hemoperitoneum on rupture), hemorrhagic cyst
• Workup: Pelvic US (complex cyst with internal echoes, "fishnet" or reticular pattern); serial hematocrit if bleeding suspected
• Tx: Expectant (most resolve in 6–8 weeks); surgical intervention if hemodynamically unstable or hemoperitoneum

Berek & Novak's Gynecology — "A hemorrhagic cyst can become symptomatic, causing worsening vital signs, and require surgery. The rapidly expanding ovarian capsule or, with rupture, the blood in the peritoneal cavity is responsible for the acute pain."

6. 🟠 Ovarian Torsion

• Mechanism: Ovary (often with an associated cyst) twists on its vascular pedicle → venous obstruction → edema → arterial compromise → ischemia/necrosis
• Symptoms: Sudden-onset severe unilateral pelvic pain, often intermittent (partial torsion); nausea and vomiting; low-grade fever late
• Risk factor: Large ovarian cyst (>5 cm increases risk), endometrioma, dermoid cyst
• Workup: Pelvic US with Doppler (absent or reversed blood flow is diagnostic but absent flow is not always present); diagnosis often clinical → laparoscopy
• Tx: Emergency surgical detorsion ± cystectomy; salpingo-oophorectomy if necrosis confirmed

Berek & Novak's Gynecology — "Ovarian torsion typically presents as acute onset of unilateral, intermittent pain and is a diagnosis of exclusion unless absent blood flow to the ovary is demonstrated via Doppler ultrasound imaging."

7. 🟠 Pelvic Inflammatory Disease (PID) / Salpingo-Oophoritis

• Mechanism: Ascending infection from cervix (Chlamydia trachomatis, Neisseria gonorrhoeae, anaerobes) → endometritis → salpingitis → oophoritis → tubo-ovarian abscess
• Symptoms: Bilateral lower abdominal/pelvic pain, abnormal vaginal discharge, fever; cervical motion tenderness + uterine + adnexal tenderness on exam; abnormal uterine bleeding in ~1/3 of patients
• Atypical presentation: Subacute or partially treated → minimal fever, chronic pelvic pain, dysmenorrhea
• Workup: NAAT for chlamydia/gonorrhea, wet mount, pelvic US (rule out TOA), βhCG
• Tx: Cefoxitin + doxycycline (outpatient); cefotetan + doxycycline IV (inpatient); add metronidazole for anaerobes

Harrison's Principles — "PID is associated with age <25 years and history of multiple sexual partners... Abnormal uterine bleeding may occur in about one-third of patients."

8. 🟠 Cervical Stenosis / Obstructive Outflow Tract Anomaly

• Mechanism: Narrowing or obstruction of the cervical canal (congenital or acquired) → menstrual blood cannot drain freely → hematometra → severe colicky dysmenorrhea; increased retrograde flow → promotes endometriosis
• Symptoms: Severe cyclic dysmenorrhea; scant or no menstrual flow; if complete obstruction → amenorrhea with cyclical pelvic pain; palpable midline pelvic mass (hematometra)
• Congenital causes in young women: Transverse vaginal septum, imperforate hymen, cervical atresia, Müllerian duct anomalies (bicornuate/unicornuate/didelphys uterus with obstructed horn)
• Workup: Pelvic exam (bulging hymen, vaginal mass), pelvic US (fluid-filled uterus), MRI (best for Müllerian anatomy)
• Tx: Cervical dilation, hysteroscopic incision; correction of Müllerian anomaly

Goldman-Cecil Medicine — "Congenital abnormalities, such as atresia of a portion of the distal genital tract and cystic duplication of the paramesonephric ducts; and cervical stenosis" are causes of secondary dysmenorrhea.

9. 🟡 Polycystic Ovary Syndrome (PCOS)

• Mechanism: Chronic anovulation → prolonged unopposed estrogen → endometrial proliferation → irregular heavy breakthrough bleeding; multiple small follicular cysts on ovaries
• Symptoms: Irregular heavy periods (oligomenorrhea/menorrhagia), dysmenorrhea, pelvic fullness; acne, hirsutism; bilateral "necklace" follicles on US
• Key distinction: Ovarian cysts in PCOS are multiple small follicles (<10 mm each), not single large cysts; however, large dominant follicle cysts can develop
• Workup: LH:FSH ratio >2:1, elevated free testosterone, US (≥12 follicles/ovary or ovarian volume >10 mL), rule out thyroid disease, late-onset CAH
• Tx: Combined OCP, weight management, metformin; progestins for endometrial protection

10. 🟡 Endometrial Polyps

• Mechanism: Focal overgrowth of endometrial glands and stroma forming a pedunculated mass → abnormal bleeding (intermenstrual, heavy); if large, may cause dysmenorrhea
• Symptoms: Menorrhagia, intermenstrual spotting, dysmenorrhea; may be asymptomatic
• Less common in 20-year-olds but does occur; associated with tamoxifen use, estrogen excess
• Workup: Pelvic US may miss small polyps; saline infusion sonohysterography (SIS) is best noninvasive test; hysteroscopy is gold standard + allows polypectomy
• Tx: Hysteroscopic polypectomy

11. 🟡 Coagulation Disorder (e.g., von Willebrand Disease)

• Mechanism: Deficiency of von Willebrand factor or platelet dysfunction → inadequate hemostasis at endometrial shedding → severe, prolonged menorrhagia
• Prevalence: vWD affects ~1% of the population; up to 13–20% of women with menorrhagia have an underlying coagulopathy
• Symptoms: Menorrhagia since menarche; easy bruising, gingival bleeding, prolonged bleeding after surgery/dental work; family history
• Workup: CBC (thrombocytopenia?), PT/INR, aPTT, vWF antigen, vWF activity (ristocetin cofactor), Factor VIII
• Tx: Tranexamic acid, DDAVP (desmopressin), vWF concentrate, combined OCP

12. 🟡 Interstitial Cystitis / Bladder Pain Syndrome (IC/BPS)

• Mechanism: Chronic bladder inflammation → referred pelvic pain that worsens cyclically with menses (prostaglandin-mediated); shares innervation with uterus/ovaries
• Symptoms: Suprapubic/pelvic pain, urinary urgency and frequency, dysuria; pain worsens premenstrually; often coexists with endometriosis (up to 40% overlap)
• Workup: Urinalysis (negative culture), cystoscopy with hydrodistension (glomerulations, Hunner ulcers), exclusion of infection
• Tx: Intravesical DMSO, pentosan polysulfate, tricyclic antidepressants, bladder training

Berek & Novak's Gynecology — Interstitial Cystitis/Bladder Pain Syndrome listed as a urologic etiology of chronic pelvic pain, alongside endometriosis and adenomyosis.

13. 🟡 Irritable Bowel Syndrome (IBS)

• Mechanism: Visceral hypersensitivity and dysmotility → crampy lower abdominal/pelvic pain; pain worsens premenstrually due to prostaglandin-mediated bowel hypersensitivity; shares referred pain pathways with uterus
• Symptoms: Crampy lower abdominal pain relieved by defecation, alternating constipation and diarrhea, bloating; symptoms overlap with dysmenorrhea and endometriosis
• Key feature: Gastrointestinal problems account for up to 60% of cases referred for pelvic pain evaluation
• Workup: Rome IV criteria; colonoscopy/stool studies to exclude IBD, celiac; no structural findings
• Tx: Low-FODMAP diet, antispasmodics, antidepressants, cognitive-behavioral therapy

Harrison's Principles — "In up to 60% of cases, pelvic pain can be attributed to gastrointestinal problems, including appendicitis, cholecystitis, infections, intestinal obstruction, diverticulitis, and inflammatory bowel disease."

14. 🟡 Müllerian Duct Anomaly (e.g., Obstructed Uterine Horn)

• Mechanism: Incomplete fusion or canalization of Müllerian ducts → unicornuate uterus with obstructed rudimentary horn, uterus didelphys with obstructed hemivagina, or other partial obstructions → menstrual blood accumulates (hematometra/hematosalpinx) → severe cyclic pain
• Symptoms: Severe dysmenorrhea since menarche; apparently normal cycles in non-obstructed horn; pelvic mass; infertility; associated renal anomalies (~30%)
• Workup: MRI pelvis (gold standard for Müllerian anatomy), pelvic US, renal US
• Tx: Surgical excision of obstructed horn, septum resection, or reconstruction depending on type

15. 🟡 Pelvic Congestion Syndrome (PCS)

• Mechanism: Incompetent ovarian and pelvic veins → venous pooling/engorgement in pelvic plexus → dull aching pelvic pain that worsens with prolonged standing, late in the day, and with menstruation
• Symptoms: Dull, aching, heaviness-type pelvic pain worst premenstrually and with standing; dyspareunia; dysmenorrhea; may have associated vulvar or lower limb varices; worsens postcoitally
• Key distinction: Pain is non-cyclic but exacerbated premenstrually; worsens with prolonged standing (unlike endometriosis)
• Workup: Pelvic US (dilated tortuous ovarian veins >6 mm), MRI, ovarian vein venography (gold standard), CT
• Tx: Medroxyprogesterone acetate (suppresses ovarian activity), GnRH agonists, gonadal vein embolization, surgical ligation

Berek & Novak's Gynecology — "Pelvic Congestion" is listed as a distinct reproductive tract cause of chronic pelvic pain.

Summary Table

Clinical Prioritization in a 20-Year-Old

• Ectopic pregnancy → βhCG first (confirmed negative = proceed)
• Ovarian torsion → emergency US with Doppler
• Hemorrhagic cyst with hemoperitoneum

1. Endometriosis — explains ovarian cysts, severe dysmenorrhea, heavy bleeding together
2. Adenomyosis — explains heavy bleeding + progressive dysmenorrhea
3. Cervical stenosis with outflow obstruction — explains severe cramps + heavy retained menstruation
4. Primary dysmenorrhea — if all structural causes excluded

1. βhCG (exclude pregnancy)
2. CBC, coagulation screen (exclude vWD)
3. STI screen (NAAT for CT/GC)
4. Transvaginal ultrasound
5. MRI pelvis (Müllerian anatomy, adenomyosis, deep endometriosis)
6. Diagnostic laparoscopy ± hysteroscopy (gold standard for endometriosis, polyps)