What is Seborrheic Keratosis?

Seborrheic Keratosis: Clinical Overview

Seborrheic keratosis (SK) is the most common benign epidermal tumor in humans, presenting as stuck-on, waxy, keratotic lesions that increase in frequency with age and affect approximately 83 million Americans. 1, 2

Clinical Presentation

Appearance and Distribution:

• SK lesions typically appear as symmetric, waxy, keratotic growths with a characteristic "stuck-on" appearance 3
• Most commonly occur on the face and upper trunk, but can develop on any body site except palms and soles 1
• Lesions are macular or papular, often pigmented, and gradually increase in size, thickness, and pigmentation over time 2
• Color ranges from tan to brown to black, with yellow-brown variations possible 3

Epidemiology:

• Extremely common in individuals over age 50, though can occur in younger adults and adolescents 1, 4
• Shows male gender preponderance 4
• Most patients have multiple lesions; 33% of SK patients have more than 15 lesions 2

Clinical Variants and Symptoms

Common Presentations:

• Multiple clinical and histological subtypes exist based on appearance 1
• Irritated seborrheic keratosis can show inflammation and commonly presents with itching 5
• Pruritus (itching) is a common feature of SK lesions and was historically overemphasized as a melanoma warning sign, leading to excessive referrals 5

Pathogenesis

Contributing Factors:

• Age is an independent risk factor 4
• Genetic predisposition plays a role 1
• Ultraviolet radiation exposure is a likely contributing factor, altering biochemical concentrations of factors like glutamine deaminases, endothelin, and stem cell factor 1, 4
• Oncogenic mutations involving FGFR-3 and FOXN1 have been identified, though these do not carry risk of malignant transformation 6, 4
• Genital involvement has been associated with human papillomavirus infection 4

Diagnostic Considerations

Clinical Diagnosis:

• Diagnosis is usually made clinically based on the characteristic stuck-on, symmetric, keratotic appearance 1
• Dermoscopy is a valuable noninvasive diagnostic tool that improves diagnostic accuracy and helps differentiate SK from malignant lesions 3, 4
• Reflectance confocal microscopy (RCM) may be used in specialized settings, though it has limitations for very thickened or ulcerated lesions 7

Critical Pitfall - Mimicry of Malignancy:

• Many SK lesions manifest morphology resembling melanoma or squamous cell carcinoma, and cases of melanoma mimicking SK have been documented 3, 7
• Photographic evaluation alone is not sufficient for definitive diagnosis 7
• Skin cancers can mimic SK or arise in association with SK 3

When to Suspect Malignancy:

• Apply the revised checklist for suspected malignant melanoma: change in size, change in shape, change in color, diameter ≥ 7 mm, inflammation, sensory change, and crusting or bleeding 7
• For uncertain diagnosis, complete excision with a narrow 2 mm rim of normal skin should be performed, with tissue sent for histopathological examination 7

Management

Indications for Treatment:

• SK is biologically benign and does not require removal for medical reasons 2
• Most patients seek removal for cosmetic concerns, particularly for facial lesions 2, 4
• Treatment may be indicated for traumatized or symptomatic lesions 2

Treatment Options:

• Dermatologists treat approximately 43% of SK patients to remove lesions 2
• Cryosurgery is the most commonly employed removal method 2
• Other effective methods include shave excision, electrodesiccation, curettage, or combinations thereof 2
• Ablative laser therapy is effective 6
• Topical treatment with 40% hydrogen peroxide and nitric-zinc complex has been investigated 6
• Nanosecond-pulsed electric field technology is a promising new technique with fewer side effects 4

Treatment Considerations:

• Each removal method has potential drawbacks including post-procedure depigmentation, scarring, and recurrence 2, 4
• Careful patient selection is required to optimize cosmetic results, particularly in skin of color patients and those with thick or numerous lesions 2
• No effective topical therapeutic agent has been fully developed, representing an area of unmet need 2