Benign Lichenoid Keratosis

This asymptomatic lesion on the upper arm of a 60-year-old man had been present for 2 years. The patient had used several over-the-counter antifungal and hydrocortisone creams to treat what he thought was ringworm.

When the patient finally sought medical advice, the lesion was excised in the office, writes Robert P. Blereau, MD of Morgan City, La. Microscopic pathologic examination revealed a psoriasiform lichenoid process with superficial and deep perivascular lymphocytic infiltrate, which suggested a lichen planus–like keratosis. Similar patterns can be seen in lichenoid dermatitis-such as fixed drug eruption-and, less commonly, in lupus erythematosus, parapsoriasis en plaques, and regressing melanocytic lesions.

This lesion is a variant of actinic keratosis. It may progress to basal cell or squamous cell carcinoma; these lesions' potential for malignant transformation is controversial.