Isomorphic Response in Seborrheic Keratosis

An 18-year-old white female abraded the upper right side of her back on the wall of a salt-water swimming pool in Florida in August, 1956. One year later, the patient noted the onset of multiple pigmented lesions confined to the area of the previous abrasion. During the past 4 years the lesions have become more numerous and have increased very slowly in size. The lesions have been asymptomatic. Examination of the remainder of the integument revealed numerous nevi but no other seborrheic keratoses. Biopsy of a lesion revealed hyperkeratosis, papillomatosis, a few keratin cysts, and increased amounts of pigment in the basal-cell layer throughout the lesion. The lesions, both clinically and histologically, were typical of seborrheic keratosis. Because of the often repeated suspicion of the infectious etiology of this and other types of tumors,1it was felt this case would be of interest, especially in view of the