Acanthosis nigricans. This is a descriptive term for a velvety or verrucous brown-to-black area of hyperkeratosis. The axilla and posterior are the most common locations, but lesions are also seen on the anterior neck and in the groin. Less commonly, there is involvement in the antecubital and popliteal fossae, on the knuckles, and in other, nonflexural areas. Onset may occur during childhood or adult life. The histologic pattern is that of hyperkeratosis and papillomatosis; the brownish discoloration seems to be caused by these surface changes rather than by any local increase in the amount of melanin. Illustrated here are lesions of acanthosis nigricans on the anterior neck and in the axilla.
Urticaria. Wheals with white-to-light-pink color centrally and peripheral erythema in a close-up view. These are the classic lesions of urticaria. It is characteristic that they are transient and highly pruritic.
Geographic tongue. There is a peculiar condition of the tongue that takes the form of denudations of the lingual surface in patches of redness that shift in position from time to time over hours and days. The cause of the condition is not known; there may be some relationship to psoriasis. No treatment is effective. The condition is largely asymptomatic except for slight tingling when sharp food is taken.