Most Likely Diagnosis: Uterine Fibroids (Leiomyoma)
The most likely cause is uterine fibroids (leiomyoma), given the classic presentation of prolonged menorrhagia with an enlarged, irregular uterus on physical examination.
Clinical Reasoning
The key diagnostic features that point to uterine fibroids include:
- Enlarged, irregular uterus on palpation - This physical finding is pathognomonic for fibroids, as the irregular contour reflects multiple fibroid nodules distorting the normal uterine architecture 1
- Prolonged, excessive menstrual bleeding for 6 months - Fibroids are among the most common structural causes of abnormal uterine bleeding in premenopausal women, with heavy or prolonged menstrual bleeding being a cardinal symptom 1, 2
- Chronicity of symptoms - The 6-month duration suggests a structural rather than hormonal etiology 3
Differential Diagnosis Analysis
Why Not Dysfunctional Uterine Bleeding (DUB)?
- DUB is a diagnosis of exclusion that requires ruling out structural causes first 3
- The enlarged, irregular uterus on exam definitively indicates structural pathology, making DUB incompatible with this presentation 3
- DUB typically presents with a normal-sized, regular uterus 3
Why Not Adenomyosis?
- While adenomyosis can cause menorrhagia and an enlarged uterus, the uterus is typically uniformly enlarged and boggy, not irregular 1
- Adenomyosis may coexist with fibroids but the irregular contour specifically suggests discrete fibroid masses 1
- The irregular surface is the distinguishing feature favoring fibroids over adenomyosis 1
Why Not Endometrial Carcinoma?
- Endometrial cancer typically does not cause significant uterine enlargement or irregularity on physical exam 1
- While endometrial cancer causes abnormal bleeding, the uterus usually remains normal in size until very advanced disease 1
- The irregular, enlarged uterus is inconsistent with typical endometrial cancer presentation 1
Epidemiology Supporting This Diagnosis
- Uterine fibroids are the most common benign tumors in women of reproductive age, with prevalence reaching 70% by age 50 4
- Fibroids are the most common tumor of the reproductive tract and frequently present with abnormal uterine bleeding 5, 6
- In premenopausal women with abnormal uterine bleeding, leiomyomas are one of the three most common structural causes alongside polyps and adenomyosis 1
Clinical Pitfalls to Avoid
Do not assume DUB without excluding structural causes - The physical examination finding of an enlarged, irregular uterus mandates imaging to characterize the structural abnormality 3
Do not delay imaging - Transvaginal ultrasound should be performed as first-line imaging to confirm fibroids and exclude other pathology 1, 7
Consider endometrial sampling if risk factors present - If the patient is >45 years old, obese, diabetic, hypertensive, or has other risk factors for endometrial cancer, endometrial biopsy is mandatory despite the likely fibroid diagnosis 3