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Many skin conditions that affect the arms result from their direct exposure to sunlight, contact with 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 phenomenon) in certain diseases such as psoriasis and lichen planus. Some skin diseases have a predilection for specific locations on the arms. While it is unknown why many dermatoses tend to localize to certain anatomical locations, lesion distribution is frequently a very important clue to establish diagnosis.
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APPROACH TO DIAGNOSIS
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Skin diseases involving the arms can be broadly placed into the following categories starting with the most common diseases (Table 37-1).
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Inflammatory Dermatoses
Infectious Diseases
Infestations and bites
Immunobullous Diseases
Autoimmune Diseases
Neoplastic
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