A 54-year-old man presents with a 3-year history of a gradually enlarging, asymptomatic lesion of the hand. He relates this to a cigar burn that he sustained from an irate girlfriend.

Annular plaque with a thin thready border of scale.

Differential diagnoses

TINEA MANUUM (superficial fungal infection of the hand) is typically annular and has a scaly border. The thin, thready border is somewhat atypical, but a microscopic examination or culture would be needed to absolutely rule this out.

GRANULOMA ANNULARE produces one or more annular plaques which often appear on the hands. With rare exceptions, a thready, scaly border is not seen in this purely dermal disease.

ANNULAR SARCOIDOSIS occasionally has scale on the border of the lesions, but seldom appears as a solitary plaque on the hand.

ERYTHEMA ANNULARE CENTRIFIGUM is one of the figurate erythemas which represents a hypersensitivity reaction to malignancy, infection, or drugs. It does have an annular configuration and is scaly at the border, but the scale trails after the advancing red rim rather than being on it, as seen here.

POROKERATOSIS is the correct diagnosis. This is a clonal disorder of keratinization that results in a thready scale on the advancing border of one or more skin lesions.

The lesion was treated by cryosurgery and the patient was then lost to follow-up.

Diagnostic pearl

Consider porokeratosis if there is an annular plaque with a thin, thready, scaly border.

Suggested reading

Pizzichetta MA, Canzonieri V, Massone C, Soyer HP. Clinical and dermoscopic features of porokeratosis of Mibelli. Arch Dermatol. 2009;145(1):91-92.

Goebeler M, Brocker EB, Hamm H. Keratotic plaques on the left trunk area and all extremities: porokeratosis. Arch Dermatol. 2006;142(8):1059-1064.

Dr Levine is in the private practice of dermatology in Tucson, Arizona.