What are the differential diagnoses for a female patient with left lower quadrant (LLQ) pain, improved with ibuprofen (ibuprofen) 400-600mg every 8 hours, accompanied by spotting between periods and heavy menstrual bleeding?

Differential Diagnoses for Left Lower Quadrant Pain with Menstrual Irregularities

Three Most Likely Diagnoses

Based on the presentation of severe LLQ pain (8/10) that responds completely to NSAIDs, combined with spotting between periods and heavy menstrual bleeding, the three most likely diagnoses are: (1) endometriosis with deep infiltrating disease, (2) adenomyosis, and (3) ovarian endometrioma.

1. Endometriosis (Deep Infiltrating Endometriosis)

• Endometriosis is a common cause of cyclical pelvic pain and abnormal uterine bleeding in reproductive-age women 1
• The combination of severe dysmenorrhea with spotting between periods increases the likelihood of endometriosis to 59-63% when combined with other symptoms 2
• Deep infiltrating endometriosis, particularly involving the uterosacral ligaments, presents with severe pain that characteristically responds well to NSAIDs like ibuprofen 3, 2
• In young women with severe dysmenorrhea (VAS ≥7), ultrasound-detected endometriosis features are found in 35.3% of cases, with uterosacral ligament fibrotic thickening present in 48.1% 2
• NSAIDs are first-line therapy for endometriosis-related pain, which explains the complete relief with ibuprofen every 8 hours 3
• Heavy menstrual bleeding occurs due to endometrial polyps, adenomyosis, or leiomyomas that frequently coexist with endometriosis 1

2. Adenomyosis

• Adenomyosis is a structural cause of abnormal uterine bleeding that commonly presents with heavy menstrual bleeding and pelvic pain 1
• In young women with severe dysmenorrhea, adenomyosis is detected in 51.1% of patients with endometriosis features on ultrasound, and appears as an isolated finding in 21.4% 2
• Adenomyosis causes both heavy menstrual bleeding and intermenstrual spotting due to ectopic endometrial tissue within the myometrium 1
• The pain responds well to NSAIDs because adenomyosis involves prostaglandin-mediated inflammation 4
• Transvaginal ultrasound can diagnose adenomyosis even in young patients, showing myometrial thickening and heterogeneity 1, 2

3. Ovarian Endometrioma

• Ovarian endometriomas are found in 41.2% of young women with ultrasound-detected endometriosis, and can present as isolated lesions in 16.8% of cases 2
• Endometriomas cause pain through local inflammation, adhesion formation, and mass effect on surrounding structures 3
• The left-sided location matches the LLQ pain distribution 2
• Associated abnormal uterine bleeding occurs through disruption of normal ovarian function and coexisting endometrial pathology 1
• Ibuprofen provides relief by inhibiting prostaglandin synthesis, which is elevated in endometriosis 4, 5

Critical Diagnostic Approach

Immediate Next Steps

• Order transvaginal ultrasound (or transrectal if not sexually active) as the first-line imaging modality 1, 2
• Transvaginal ultrasound has high specificity for detecting endometriomas, adenomyosis, and deep infiltrating endometriosis when performed by an expert sonographer 2
• Young patients with severe dysmenorrhea should be referred to an expert sonographer to minimize diagnostic delay 2

If Ultrasound is Inconclusive

• MRI abdomen and pelvis should be considered if ultrasound cannot completely visualize the endometrium or if deep infiltrating endometriosis is suspected 1
• MRI has excellent tissue contrast resolution and multiplanar capability for visualizing endometriosis, adenomyosis, and endometriomas even when leiomyomas are present 1
• However, MRI has poor sensitivity (56%) for identifying structural gynecologic causes of chronic pelvic pain and may miss 46% of cases 6

Alternative Diagnoses to Exclude

• Diverticulitis is unlikely given the patient's age, menstrual symptom correlation, and complete response to ibuprofen alone 1, 7
• Diverticulitis typically requires CT imaging and presents with fever, leukocytosis, and does not correlate with menstrual cycles 1
• Functional bowel disorders become likely only after structural pathology has been excluded by imaging and colonoscopy 8

Management Implications

• Continue ibuprofen 400 mg every 8 hours during menstruation, as this is FDA-approved for dysmenorrhea and provides effective pain control 4
• Ibuprofen inhibits prostaglandin synthesis, reducing both pain and menstrual blood flow 4, 5
• Prophylactic ibuprofen starting 24 hours before expected menstruation significantly reduces pain intensity from 9.47 to 3.0 (mild) over 48 hours 5
• If endometriosis is confirmed, oral contraceptives should be considered as second-line therapy after NSAIDs 3
• Surgical management (laparoscopy) should be reserved for cases where medical therapy fails or when fertility preservation is a concern 3, 6

Red Flags Requiring Urgent Evaluation

• Development of fever, inability to pass gas/stool, severe tenderness with guarding, vomiting, or bloody stools would require immediate CT imaging to exclude diverticulitis, perforation, or other surgical emergencies 8, 7
• Weight loss, anemia, or change in bowel habits warrant colonoscopy to exclude malignancy 8