What is the differential diagnosis for a localized, scaly lesion that is slightly greasy and easily removed by curettage (curettage), particularly in an adult or elderly individual?

Differential Diagnosis of Localized Scaly Lesions That Are Slightly Greasy and Easily Removed by Curettage

The primary differential diagnosis for a localized, scaly, slightly greasy lesion that is easily removed by curettage includes seborrheic keratosis, actinic keratosis (particularly hypertrophic variants), Bowen's disease (squamous cell carcinoma in situ), and superficial basal cell carcinoma.

Primary Diagnostic Considerations

Seborrheic Keratosis (Most Likely)

• Seborrheic keratosis is the most common benign skin tumor in humans and characteristically presents as a "stuck-on," waxy, keratotic lesion that is easily removed by curettage 1, 2.
• These lesions typically have a slightly greasy appearance and can be removed with simple curettage, making this the most likely diagnosis given the clinical description 3.
• SK affects approximately 83 million Americans and shows increasing prevalence with age, though it can occur in younger individuals 1.
• The lesions are biologically benign and do not require removal for medical reasons unless histologic confirmation is needed or they become symptomatic 1.

Clinical pitfall: Pigmented and inflamed seborrheic keratoses may mimic melanoma, basal cell carcinoma, or pigmented actinic keratosis, and dermoscopic examination may be inconclusive 4. When clinical features are atypical or the lesion shows recent changes, biopsy is mandatory 5, 4.

Actinic Keratosis (Hypertrophic Variant)

• Actinic keratoses present as discrete patches of erythema and scaling on sun-exposed skin in middle-aged and elderly individuals 6.
• Hypertrophic AKs are thicker, more keratotic lesions that may be amenable to curettage, though they require more aggressive treatment than thin AKs 6.
• These lesions occur predominantly on chronically sun-exposed areas such as the face, scalp, and dorsa of hands in fair-skinned individuals 6.
• For hypertrophic AKs where squamous cell carcinoma is in the differential diagnosis, curettage with two or three cycles may be warranted to ensure adequate treatment 6.

Critical distinction: If a lesion fails to respond to standard AK therapy, further evaluation with histology is essential to rule out invasive squamous cell carcinoma 6.

Bowen's Disease (SCC in situ)

• Bowen's disease represents full-thickness epithelial atypia and can be difficult to distinguish histologically from bowenoid actinic keratosis 6.
• Curettage with cautery is a simple, inexpensive, safe, and effective method for treating SCC in situ, with better outcomes than cryotherapy in terms of pain, healing, and recurrence rate 6.
• These lesions may present as scaly, erythematous patches that can be localized 6.

Superficial Basal Cell Carcinoma

• Superficial BCC can present as scaly patches and may be confused with actinic keratosis 6.
• Curettage and electrodesiccation achieves 5-year cure rates of 91-97% for properly selected low-risk BCCs 6.
• However, this technique should not be used in areas with terminal hair growth or if the subcutaneous layer is reached during surgery 6.

Algorithmic Approach to Diagnosis

Step 1: Patient Demographics and Location

• Age over 50 years + non-sun-exposed areas → favor seborrheic keratosis 1, 2
• Middle-aged/elderly + chronically sun-exposed skin (face, scalp, hands) → favor actinic keratosis 6

Step 2: Lesion Characteristics

• "Stuck-on" appearance, waxy, easily removed with minimal bleeding → seborrheic keratosis 1, 3
• Rough, sandpaper-like texture with erythema on sun-damaged skin → actinic keratosis 6
• Persistent, slowly enlarging scaly patch → consider Bowen's disease 6

Step 3: Response to Curettage

• If the lesion removes easily in one pass with clear demarcation → likely seborrheic keratosis 2, 3
• If firm dermis is not reached or tissue appears soft → consider malignancy and perform excision instead 6
• If curettage specimen shows atypical features → perform two additional cycles to ensure adequate treatment if SCC is possible 6

Step 4: Mandatory Histologic Evaluation

Always obtain histology in the following scenarios:

• Lesions failing to respond to standard therapy 6
• Diagnostic uncertainty between benign and malignant lesions 6
• Recent change in color, size, or symptoms 4
• Atypical clinical or dermoscopic features 5, 4
• Hypertrophic or isolated lesions that could represent invasive SCC 6

Treatment Implications Based on Diagnosis

If Seborrheic Keratosis

• Removal is for cosmetic purposes only; no medical necessity unless symptomatic 1
• Curettage is an effective and commonly employed removal method 1, 2
• Cryosurgery is the most common removal method used by dermatologists 1

If Actinic Keratosis

• For hypertrophic AKs, curettage is rated as the best treatment option (••••) compared to other modalities 6
• Histology may be required, and formal excision may be preferred for isolated hypertrophic lesions 6
• Curettage addresses focal lesions but does not treat the field of actinic damage 6

If Bowen's Disease or BCC

• Curettage with cautery or electrodesiccation is effective for properly selected lesions 6
• Avoid curettage in high-risk locations or if subcutaneous fat is reached 6
• Consider excision with margin assessment for definitive treatment 6

Critical Pitfalls to Avoid

• Never assume a "benign-appearing" lesion is seborrheic keratosis without considering malignancy, especially in sun-exposed areas 5, 4
• Do not use curettage in areas with terminal hair growth (scalp, beard, pubic areas) due to risk of incomplete removal of follicular extension 6
• If subcutaneous fat is reached during curettage, stop and perform surgical excision instead 6
• Pigmented and inflamed seborrheic keratoses may lack typical dermoscopic features and mimic melanoma—biopsy all equivocal lesions 4
• Failure to obtain histology on treatment-resistant lesions may miss invasive squamous cell carcinoma 6