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Many skin conditions that affect the arms result from exposure to sunlight, contact allergens or irritants, trauma, bug bites, and other environmental insults. The arms are within close reach of the contralateral hand so patients can easily scratch pruritic dermatoses. Scratching or trauma may produce a linear streak of papules (Koebner reaction) in certain diseases such as lichen planus and psoriasis. Some skin diseases have a predilection for specific locations on the arms. While it is unknown why many dermatoses have a tendency to localize to certain anatomical locations, lesion distribution is frequently a very important clue to establish diagnosis.


Skin diseases primarily involving the arms can be broadly categorized according to their etiology. These include inflammatory, infectious, neoplastic, and photodermatoses (see Table 32-1). The distribution of skin lesions is often helpful in diagnosing skin diseases located on the arms. For example, psoriasis usually favors the extensor surface (especially the elbows), photodermatoses affect areas exposed to light, keratosis pilaris is typically seen on the proximal dorsal arms, and atopic dermatitis generally affects the extensor surface in infants and flexural surface in children and adults. Lichen planus is commonly located on the volar wrist and flexural surfaces and nummular dermatitis on extensor surfaces.

Table 32-1.Differential diagnosis for diseases of the arms.

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