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KEY POINTS

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  • In a patient with a dermatologic condition, observation and description of the lesions (morphology, distribution, and texture) are important for developing a differential diagnosis.

  • Mucous membranes (oral, ocular, nasal, genital, and perianal) should be examined in all patients.

  • The skin may provide clues to an underlying, life-threatening condition, such as endocarditis, graft-versus-host disease, bacterial and fungal sepsis, toxic shock syndrome, systemic vasculitis, or complications from the human immunodeficiency virus.

  • Drug-related dermatoses are prevalent in the intensive care unit. Clues to diagnosis include a rapidly developing eruption; generalized, symmetrical, predominantly truncal distribution; morbilliform, urticarial, or acneiform morphology; and accompanying pruritus.

  • Extensive skin disease can cause important fluid, electrolyte, and protein losses and predisposes the patient to life-threatening infections.

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BASICS OF DERMATOLOGY

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APPLICATION OF STRUCTURE AND FUNCTION TO DERMATOSES
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The basic anatomy of the skin is described in Figure 129-1. The skin is a complex organ whose major function is to provide a barrier against the environment. Other major functions include temperature regulation and sensation. The skin has three major layers: epidermis, dermis, and subcutaneous tissue. The outermost layer of the epidermis, the stratum corneum, is composed of dead, anucleate keratinocytes and serves as the first and major physical barrier. The stratum granulosum and stratum spinosum lie below the stratum corneum and are composed of keratinocytes in the process of differentiation. They are derived from the bottom layer of the epidermis, the basal cell layer. The epidermis is connected to the dermis by a complex of proteins and adhesion molecules in the basement membrane zone. Nutrients and products of metabolism are exchanged in the superficial and deep vascular networks located in the dermis. The dermis also contains nerve endings and supporting structures such as sebaceous glands, eccrine sweat glands, and hair follicles.

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FIGURE 129-1

Structure of normal skin. (Used with permission of Dr Jie Song.)

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Alteration of any layer or structure of the skin can result in primary dermatologic disease. Often the skin is secondarily affected in underlying comorbid conditions and may serve as a window to internal disease processes. The stratum corneum can be damaged in the intensive care setting by tape, electrocardiographic leads, defibrillator devices, dry environments, pressure, or adhesives. Alteration may impair barrier resistance to infectious agents or allow passage of antigens to deeper layers of the skin. Preparing the skin for invasive procedures with topical solutions exposes the patient to potential sensitizers. Metabolically active cells in the suprabasal layers are susceptible to inflammatory and cytotoxic reactions from medications and toxins. Disruption in cell adhesion clinically manifests as blisters and may result from medications, toxins, pressure, extremes in temperature, or autoimmune diseases. Infections and inflammatory processes can occur at any level or in any structure, leading to conditions such as impetigo, folliculitis, cellulitis, fasciitis, or vasculitis.

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