The skin shields the internal organs from harmful xenobiotics in the environment and maintains internal organ integrity. The adult skin covers an average surface area of 2 meters2. Despite its outwardly simple structure and function, the skin is extraordinarily complex. The skin can be affected by xenobiotic exposures that occur through any route. Dermal exposures account for a few percent of the cases and for approximately 1% of the fatalities reported to the American Association of Poison Control Centers (AAPCC) (Chap. 135). The principles of an adverse cutaneous reaction can be used to make relevant predictions, such as the physical and chemical properties of the xenobiotic and whether the effect of a response will be local or systemic. The clinician must obtain essential information as to the dose, timing, route, and location of exposure. The location of xenobiotic injury determines the histologic morphology, the severity of the reaction pattern, and the overall clinical findings. It should be noted, however, that different xenobiotics may produce clinically similar skin changes and conversely that many xenobiotics may produce diverse dermal lesions. The classical dermatologic lesions are defined in Table 29–1. The dermatology lexicon to assist the clinician is available at www.dermatologylexicon.org.
Table 29–1. Dermatologic Diagnostic Descriptions of Lesions of the Skin |Favorite Table|Download (.pdf)
Table 29–1. Dermatologic Diagnostic Descriptions of Lesions of the Skin
|Primary Cutaneous Lesions||Secondary Cutaneous Lesions|
|Bulla: a circumscribed collection of free fluid > 0.5 cm in diameter||Erosion: a loss of the epidermis up to the full thickness of the epidermis but not through the basement membrane|
|Comedone: open and closed dilated pores (blackheads and whiteheads)||Hypertrophy: a thickening of the skin|
|Macule: a circumscribed flat variation of color that may be brown, blue, yellow, red, or hypopigmented (no thickness)||Lichenification: a secondary process with noted accentuation of skin surface markings|
|Nodule: a circumscribed elevation of ≥ 0.5 cm in diameter||Scale: flaking that is separate from the original surface of a lesion|
|Papule: an elevation of < 0.5 cm in diameter||Scar: a thickened, often discolored, surface|
|Plaque: a circumscribed elevation of > 0.5 cm in diameter||Ulcer: a loss of full-thickness epidermis and papillary dermis, reticular dermis, or subcutis|
|Pustule: a circumscribed collection of leukocytes and free fluid that vary in size|
|Tumor: an elevation of > 0.5 cm in diameter|
|Vesicle: a circumscribed collection of free fluid ≥ 0.5 cm in diameter|
|Wheal: a firm edematous plaque resulting from infiltration of the dermis with fluid|
The skin has three main components that interconnect anatomically and interact functionally: the epidermis, the dermis, and the subcutis or hypodermis (Figure 29–1). The three reactive units are the superficial reactive unit; the reticular layer of the dermis; and the subcutaneous tissue.24 The primary physiologic role of the epidermis, the most external layer of the skin, is to maintain water homeostasis and to establish immunologic surveillance. It is composed of five layers: the ...