Do you recognize this annular lesion?

A 42-year-old man presents with an asymptomatic, annular, keratotic lesion of several months’ duration on his upper arm.

Can you identify this condition?

A. Actinic keratosis.
B. Seborrheic keratosis.
C. Porokeratosis.
D. Granuloma annulare.
E. Keratoacanthoma.

(Answer on next page.)

Dermclinic—Answer

Case 2:  Porokeratosis

A lesion with a keratotic rim and central clearing is typical of porokeratosis, C, which usually develops on sun-exposed skin. Typically, actinic keratoses are not as well-defined as these lesions and do not feature central clearing. Seborrheic keratoses are well-defined, flat, verrucous papules and plaques. Granuloma annulare is not keratotic; keratoacanthoma is an erythematous nodule with a central keratotic core.

Thought to be caused by a defect in keratinization, porokeratotic lesions rarely undergo malignant degeneration; therefore, treat as you would actinic keratoses, with 5-fluorouracil or cryosurgery. Shave excision is effective but usually not necessary. Some practitioners report success in treating this condition with tretinoin. ■