Seborrheic keratosis vs Actinic keratosis and solar lentigo
How to tell Seborrheic keratosis and Actinic keratosis and solar lentigo apart when a board question makes them look alike.
Seborrheic keratosis is stuck-on waxy; actinic keratosis is rough premalignant scale; solar lentigo is flat sun macule.
Side by side
Seborrheic keratosis is a benign waxy stuck-on plaque with horn cysts, common in older adults.
Actinic keratosis is a rough scaly premalignant UV-induced lesion; solar lentigo is a benign flat tan macule from sun exposure.
Benign epidermal proliferation creates stuck-on keratin-filled lesions.
Actinic keratosis reflects atypical keratinocytes from UV damage; solar lentigo reflects increased melanocytes/melanin without keratinocyte dysplasia.
Stuck-on waxy appearance and horn cysts support seborrheic keratosis.
Gritty scale and atypical basal keratinocytes support actinic keratosis; flat uniform sun spot supports solar lentigo.
The trap
Pigmented sun-exposed lesions overlap, but texture and premalignant keratinocyte atypia separate them.
The repair move
For pigmented plaques, decide stuck-on waxy growth versus gritty premalignant scale versus flat lentigo.
Try a free question
CoreA 64-year-old woman has multiple 1-2 cm well-circumscribed waxy, 'stuck-on' brown plaques on her trunk and face. The lesions have a verrucous surface and feel greasy. They have been slowly enlarging over years and are not painful or pruritic. Biopsy shows a benign keratinocyte proliferation with horn cysts. Which diagnosis is most likely?
Show answer and explanation
Answer: A. Seborrheic keratosis. Seborrheic keratosis is a benign 'stuck-on' waxy plaque with horn cysts on histology; common after age 50; not premalignant; sudden eruption of multiple SKs (Leser-Trelat sign) may indicate underlying malignancy; treatment options are cryotherapy or curettage for cosmesis.
Why the other choices are tempting
- B. Actinic keratosis is rough scaly premalignant lesion in sun-exposed areas.
- C. Solar lentigo is a FLAT brown macule in sun-exposed skin, without the verrucous waxy appearance.
- D. Melanoma has ABCDE features and pagetoid melanocyte proliferation.
- E. Verruca vulgaris is HPV-induced wart with HPV cytopathic changes.
Flashcards
Tap a card to flip it.
What appearance supports seborrheic keratosis?
A waxy stuck-on plaque supports seborrheic keratosis.
What lesion can progress to SCC?
Actinic keratosis can progress to squamous cell carcinoma.
Quick answers
What is the fastest way to tell Seborrheic keratosis from Actinic keratosis and solar lentigo?
Seborrheic keratosis is stuck-on waxy; actinic keratosis is rough premalignant scale; solar lentigo is flat sun macule.
What is the key clue for Seborrheic keratosis?
Seborrheic keratosis is a benign waxy stuck-on plaque with horn cysts, common in older adults.
What is the key clue for Actinic keratosis and solar lentigo?
Actinic keratosis is a rough scaly premalignant UV-induced lesion; solar lentigo is a benign flat tan macule from sun exposure.
What is the common trap with Seborrheic keratosis vs Actinic keratosis and solar lentigo?
Pigmented sun-exposed lesions overlap, but texture and premalignant keratinocyte atypia separate them.