How is the PALM‑COEIN classification system used to evaluate abnormal uterine bleeding in a reproductive‑age woman?

PALM-COEIN Classification System for Abnormal Uterine Bleeding

The PALM-COEIN classification system is a standardized framework that divides causes of abnormal uterine bleeding in reproductive-age women into structural (PALM) and nonstructural (COEIN) etiologies, serving as the foundation for systematic evaluation and treatment planning 1.

Understanding the Classification Structure

The acronym systematically categorizes all potential causes:

PALM - Structural Causes (Imaging-Detectable)

• P = Polyp (endometrial)
• A = Adenomyosis
• L = Leiomyoma (submucosal or other myoma)
• M = Malignancy and hyperplasia (endometrial or myometrial)

COEIN - Nonstructural Causes (Not Imaging-Detectable)

• C = Coagulopathy (bleeding disorders)
• O = Ovulatory dysfunction (oligo-ovulation/anovulation)
• E = Endometrial (primary endometrial disorders, molecular deficiencies in hemostasis regulation)
• I = Iatrogenic (exogenous hormones, intrauterine devices, medications)
• N = Not yet classified (other causes not fitting above categories)

2, 1

Clinical Application Algorithm

Step 1: Initial Assessment

After excluding pregnancy and assessing hemodynamic stability, obtain:

• Pregnancy test (beta-hCG)
• Complete blood count (assess anemia)
• Thyroid-stimulating hormone (TSH) and prolactin levels
• Coagulation studies if bleeding disorder suspected 1, 3, 4

Step 2: Risk Stratification for Endometrial Sampling

Perform endometrial biopsy in:

• All women ≥45 years old
• Women <45 years with unopposed estrogen exposure (obesity, PCOS, chronic anovulation)
• Women with risk factors for endometrial cancer regardless of age

Endometrial biopsy is preferred over dilation and curettage—it's less invasive, safer, and lower cost 1, 4.

Critical caveat: Endometrial biopsy sensitivity varies with lesion type (focal vs. diffuse), size, and location. Focal lesions like polyps may be missed 1.

Step 3: Imaging Selection

Transvaginal ultrasound (TVUS) is first-line imaging for structural evaluation 2, 4.

When TVUS is inadequate:

• Uterine position, body habitus, or pathology (adenomyosis, large leiomyomas) may limit visualization
• Upgrade to MRI with diffusion-weighted imaging for complete endometrial assessment—MRI's multiplanar capability and tissue contrast resolution overcome TVUS limitations 2
• Saline infusion sonohysterography has 96-100% sensitivity for intracavitary pathology 1

Avoid transvaginal ultrasound in virgins; use transabdominal imaging instead, though it's less sensitive for endometrial assessment 1.

Step 4: Hysteroscopy Consideration

If medical treatment fails or imaging is inconclusive, hysteroscopy allows direct visualization of the endometrial cavity and can diagnose focal lesions missed by blind endometrial sampling 1.

Prevalence Patterns and Clinical Implications

Research demonstrates that ovulatory dysfunction (AUB-O) is the most common identifiable cause (24.7-31.6%), followed by leiomyoma (13.2-16.8%) 5, 6. However, a substantial proportion (36.1%) may fall into the "not yet classified" category, highlighting diagnostic challenges 6.

Age-specific considerations:

• Younger women: Ovulatory dysfunction predominates
• Older reproductive-age women: Structural causes (leiomyoma, adenomyosis) and malignancy risk increase
• Women with AUB-M classification tend to be older 6

Associated findings:

• Anemia is more prevalent in AUB-P (polyp) cases
• Hypothyroidism and elevated TSH levels are highest in AUB-O (ovulatory dysfunction) group
• Obesity/overweight status affects 64.2% of AUB patients 5, 6

Treatment Decision Framework

Once classification is established:

For nonstructural causes (COEIN): Medical management is first-line, as imaging cannot diagnose these etiologies 2.

For structural causes (PALM): Treatment depends on specific pathology, patient age, fertility desires, and symptom severity. Hormonal treatments show effectiveness even with structural causes (OR=2.15 for improved outcomes), though leiomyoma presence decreases treatment success odds (OR=0.55) 5.

Common Pitfalls to Avoid

1. Don't use outdated terminology: Abandon terms like "menorrhagia," "metrorrhagia," and "dysfunctional uterine bleeding"—they're poorly defined and inconsistently used 7.

2. Don't skip endometrial sampling in high-risk patients: Age ≥45 years or unopposed estrogen exposure mandates tissue diagnosis to exclude malignancy 1, 4.

3. Don't rely solely on TVUS when visualization is incomplete: Adenomyosis and endometrial hyperplasia are frequently underdiagnosed by ultrasound alone; consider MRI or hysteroscopy 2, 8.

4. Don't assume single etiology: Multiple PALM-COEIN categories can coexist in the same patient—comprehensive evaluation is essential 7, 9.

The PALM-COEIN system's strength lies in its universal applicability and standardization, facilitating research comparability and clinical communication globally 7, 9. While some studies note diagnostic challenges in low-resource settings (65% preoperative accuracy), the system remains valuable for treatment planning when applied systematically 8.