A 38-year-old multiparous woman complains of progressive dysmenorrhea and menorrhagia over the past 3 years. Transvaginal ultrasound shows a heterogeneous, enlarged uterus with indistinct junctional zone. What is the most common cause of secondary dysmenorrhea in reproductive-age women?

Explanation

## Most Common Cause of Secondary Dysmenorrhea **Key Point:** Adenomyosis is the most common cause of secondary dysmenorrhea in multiparous women of reproductive age. It is characterized by ectopic endometrial glands and stroma within the myometrium, typically occurring after age 35–40. ### Causes of Secondary Dysmenorrhea: Comparative Epidemiology | Cause | Frequency | Age Group | Key Features | |-------|-----------|-----------|---------------| | Adenomyosis | 35–40% | 35–50 years | Dysmenorrhea + menorrhagia, thickened junctional zone | | Endometriosis | 30–35% | 25–40 years | Dysmenorrhea + chronic pelvic pain, chocolate cysts | | Uterine fibroids | 20–25% | 40–50 years | Menorrhagia > dysmenorrhea, submucosal/intramural | | PID sequelae | 5–10% | Variable | History of infection, adhesions | **High-Yield:** Adenomyosis is almost exclusively a disease of women who have had uterine instrumentation (D&C, curettage, hysteroscopy, termination of pregnancy). Multiparity is a major risk factor. The condition is often underdiagnosed because it requires histology for definitive diagnosis. **Clinical Pearl:** The classic triad of adenomyosis is: 1. **Dysmenorrhea** — often severe and progressive 2. **Menorrhagia** — heavy, prolonged menses 3. **Uterine enlargement** — typically 2–3× normal size, tender, boggy **Mnemonic:** **ADENO** — Adenomyosis, Dysmenorrhea, Enlarged uterus, Nulliparous (actually multiparous), Older women (>35 years). ### Pathophysiology of Adenomyosis 1. **Invagination theory** — Disruption of the endometrial–myometrial interface allows downward growth of basalis layer. 2. **De novo metaplasia** — Bone marrow–derived stem cells differentiate into endometrial tissue within myometrium. 3. **Tissue injury and repair (TIAR)** — Repeated uterine contractions and inflammation perpetuate the condition. ### Imaging Features **Transvaginal ultrasound (most sensitive):** - Thickened, indistinct junctional zone (>12 mm) - Heterogeneous myometrial echotexture - Myometrial cysts and striations - Asymmetric myometrial thickening **MRI (gold standard for diagnosis):** - T2-weighted: Low-signal junctional zone thickening - T1-weighted: Foci of hyperintensity (hemorrhage) ### Distinction from Endometriosis | Feature | Adenomyosis | Endometriosis | |---------|-------------|----------------| | Location | Within myometrium | Ectopic, outside uterus | | Age | >35 years (typically) | 25–40 years | | Parity | Multiparous | Nulliparous/infertile | | Dysmenorrhea | Progressive | Often stable | | Menorrhagia | Prominent | Variable | | Imaging | Junctional zone thickening | Ovarian cysts, nodules | [cite:DeCherney Gynecology 14e Ch 9, Berek & Novak's Gynecology 16e Ch 12, FIGO Classification of Adenomyosis 2018]