Seborreic Keratosis

Introduction

Seborrheic keratosis (SK) is a common benign epidermal tumor that presents as a well-demarcated, pigmented, verrucous, or waxy lesion with a “stuck-on” appearance. It typically occurs in middle-aged and older adults and can be found on the face, trunk, and extremities.

While seborrheic keratoses are harmless, they are often mistaken for malignant lesions, such as melanoma. Proper diagnosis and patient reassurance are essential, though lesions can be removed if symptomatic or for cosmetic reasons.

Epidemiology and Risk Factors

Prevalence:

• One of the most common benign skin tumors.
• More common after age 40 (incidence increases with age).
• Affects all ethnicities, but more noticeable in fair-skinned individuals.
• No malignant potential (does not progress to skin cancer).

Risk Factors:

• Aging – Incidence increases with age.
• Genetics – Family history may predispose individuals to multiple SKs.
• Sun exposure – May contribute but is not the primary cause.
• Friction or irritation – SKs are common in skin folds (intertriginous areas).
• Pregnancy or hormonal changes – Can trigger sudden SK development.

Pathophysiology

1. Epidermal Proliferation
   • SK results from clonal expansion of basal keratinocytes, leading to hyperkeratosis and acanthosis.
2. Activation of Oncogenes (FGFR3 Mutations)
   • Genetic studies suggest that mutations in FGFR3 (Fibroblast Growth Factor Receptor 3) play a role in keratinocyte overgrowth.
3. Accumulation of Melanin in Lesions
   • Some SKs become pigmented due to melanin deposits in keratinocytes.
4. Lack of Malignant Potential
   • SKs do not progress to skin cancer, but sudden onset of multiple lesions (Sign of Leser-Trélat) may indicate an underlying malignancy.

Clinical Features

1. General Characteristics

• Waxy, verrucous, or velvety texture.
• Well-demarcated, round, or oval lesion.
• Colors range from tan to dark brown or black.
• “Stuck-on” or “pasted” appearance.

2. Common Locations

• Trunk (most common), face, scalp, neck, upper extremities.
• Intertriginous areas (under breasts, axillae, groin).
• Palms and soles are spared.

3. Variants of Seborrheic Keratosis

Variant	Key Features
Common SK	Waxy, scaly, brown/tan plaque
Stucco keratosis	White/gray, flat, scaly plaques, often on legs
Dermatosis papulosa nigra (DPN)	Small, dark papules on face (common in darker skin tones)
Irritated SK	Inflamed, red, itchy lesion (may mimic skin cancer)

4. Sign of Leser-Trélat (Rare Paraneoplastic Syndrome)

• Sudden onset of multiple seborrheic keratoses.
• Associated with internal malignancies (e.g., gastric, lung, colorectal cancer).
• Requires further investigation if symptoms such as weight loss, night sweats, or systemic signs are present.

Diagnosis

1. Clinical Diagnosis (Most Common Approach)

• Classic “stuck-on” appearance.
• Uniform color and texture.
• No ulceration, bleeding, or rapid growth.

2. Dermoscopy (For Uncertain Cases)

• Milia-like cysts (white-yellow keratin-filled cysts).
• Comedo-like openings.
• Network-like ridges (cerebriform pattern).
• Sharp demarcation from surrounding skin.

3. Biopsy (If Malignancy Is Suspected)

• Indications for biopsy:
  • Atypical features (irregular border, rapid growth, ulceration, bleeding, asymmetry).
  • Concern for melanoma or pigmented basal cell carcinoma.
• Histopathology Findings:
  • Hyperkeratosis, acanthosis, papillomatosis.
  • Horn cysts (keratin-filled invaginations).

4. Differential Diagnosis

Condition	Key Differences
Actinic keratosis	Pre-malignant, rough texture, occurs on sun-exposed areas
Basal cell carcinoma (BCC)	Pearly border, telangiectasia, slow-growing
Melanoma	Asymmetry, irregular borders, rapid growth
Verruca vulgaris (wart)	Caused by HPV, filiform projections

Management and Treatment

1. Conservative Management (Most Cases)

• Reassurance – SKs are benign and do not require treatment.
• Monitor for changes (irregular growth, ulceration, bleeding).

2. Indications for Removal

• Symptomatic (pain, irritation, itching).
• Cosmetic concerns (especially on the face).
• Recurrent inflammation or infection.
• Uncertain diagnosis requiring biopsy.

3. Removal Techniques (For Symptomatic or Cosmetic Cases)
4. Cryotherapy (Most Common Non-Surgical Method)

• Liquid nitrogen (-196°C) applied for 5–10 seconds.
• Effective for small SKs but may cause temporary hypopigmentation.

1. Curettage (Scraping the Lesion with a Curette)

• Often combined with electrocautery for hemostasis.
• Used for larger, thicker SKs.

1. Shave Excision

• Performed for raised lesions using a scalpel.
• Minimal scarring.

1. Laser Therapy (Carbon Dioxide or Erbium-YAG Laser)

• Good for facial SKs and dermatosis papulosa nigra.
• Less risk of scarring but expensive.

1. Topical Treatments (Limited Use)

• Hydrogen peroxide 40% (Eskata) – FDA-approved for superficial SKs.
• Retinoids (e.g., Tretinoin, Calcipotriol) – May help flatten lesions.

Complications

• Post-treatment hypopigmentation or hyperpigmentation (especially in darker skin tones).
• Bleeding or scarring after removal.
• Misdiagnosis of a malignant lesion (e.g., melanoma masquerading as SK).

Prevention Strategies

• Sun protection (broad-spectrum sunscreen, sun-protective clothing).
• Avoid friction or trauma to predisposed areas.
• Routine skin checks for new lesions.

Prognosis and Follow-Up

• Benign condition with no malignant potential.
• New lesions may continue to develop with aging.
• Patients should be advised to seek medical review if lesions change rapidly.

Conclusion

Seborrheic keratosis is a common, benign skin lesion characterized by a “stuck-on” appearance, waxy texture, and slow growth. It has no malignant potential, but sudden multiple lesions may indicate paraneoplastic syndrome (Sign of Leser-Trélat). Diagnosis is clinical, with biopsy reserved for atypical cases. Treatment is unnecessary unless symptomatic or cosmetically concerning, with cryotherapy, curettage, or laser therapy as removal options. Patient education and reassurance are crucial to avoid unnecessary anxiety.