Solitary patches of keratosis may develop in the elderly, usually upon the face or the hands (Fig. 4). They start as papules from 1 to 3 mm. in diameter, and are of great surface hardness, due to a piling up of the horny layer. This thickening of the keratin soon becomes black in color. The crust is very adherent, and usually becomes detached only once or twice a year. They rarely grow to more than 5 mm. in diameter, and are sometimes multiple, although it is rare to find more than three or four such lesions in any one person.
Histologically, the changes are very similar to those described as occurring in senile warts, but there are no signs of an undue amount of fat being present.
These patches niay become malignan the finrt change noted being ulceration and serous discbarge.
Fig. i.-patient, a very old man. has had this horny growth upon his hand for about a year. It was cured by excision. (Author's collection).
Treatment is identical with that described under senile warts.