Maria Isabel Romano Skin problems occur often in the general population and are the presenting complaint in many primary care patients.1 A large number of skin diseases manifest in similar ways. Factors such as age, ethnic and genetic makeup, risk factors, body habitus, skin surface, and self-care practices may complicate a diagnosis by altering the appearance and distribution of lesions that are characteristic of the skin disorder. Underlying systemic pathologic conditions may also contribute to the difficulty of making a definitive diagnosis of skin lesions. The primary functions of the skin are protection of the underlying body structures from the entrance of microorganisms, control of body heat and elimination of body waste through perspiration, and prevention of injury to core body structures. The skin protects the body from infectious agents; protects against loss of body heat through conduction, convection, and radiation; and provides a first-line defense against mechanical, chemical, and thermal injury. Glands in the dermal layer of the skin secrete a substance that lubricates the body surface and assists with a variety of body functions. The peripheral sense receptors contained in the skin alert the body to pain, temperature changes, pressure, and touch. The skin is composed of three layers: the epidermis, the dermis, and the hypodermis or subcutis. The outer epidermal, or cuticle, layer is avascular and is divided into an outer horny layer (the stratum corneum) and an underlying horny layer (the stratum mucosum). The stratum corneum consists of keratinocytes—cells that originate in the basal cell layer of the epidermis and migrate upward to the stratum corneum and slough off as dead cells, called squames. As long as the stratum corneum (the outer horny layer) is intact, normal skin bacteria are prevented from invading deeper skin and gaining access to the bloodstream. The lower layer of the epidermis contains the Langerhans cells, which function as antigen-presenting cells that migrate to the lymph nodes and play an important role in the allergic skin response. Melanocytes found in the basal layer of the epidermis constitute the body’s principal protection against ultraviolet (UV) radiation.2 The second layer of the skin, the dermis (also termed the cutis, corneum, or true skin), holds the epidermis in place. The dermis is composed of an outer papillary layer and an inner reticular layer that contains connective tissue and the blood supply as well as lymphatic vessels, peripheral nerves, elastic tissue, and a reservoir of water and electrolytes. The dermal appendages are contained within the reticular layer and include the eccrine sweat glands that serve to control body temperature by evaporation, the sebum-producing sebaceous glands that lubricate the stratum corneum through openings in the skin (called pores), the hair follicles, and the nail bed. Other appendages include apocrine glands attached to hair shafts located in the axillary, perianal, and genital areas. These glands respond to the increased hormone levels associated with puberty, adolescence, and young adulthood and decrease their activity with normal aging. A variation of the apocrine gland is the cerumen-producing glands lining the external auditory canal. The oily substance, cerumen, serves to protect the skin lining the ear canal from bacterial invasion. A third layer of the skin, the hypodermis or subcutis, functions to store fat, to insulate the body from extremes in temperature, and to provide a cushion against injury. It also contributes to the skin’s mobility over underlying body parts. With age, both structural and functional changes occur in the skin. These changes include decrease in the number of Langerhans cells; variation in size, shape, and staining of the keratinocytes; decrease in the thickness of the dermis; and loss of elastic tissue. There is a decrease in the number of sweat glands, hair follicles, and specialized nerve endings as well as decreased vascularity and increased fragility of existing capillaries. Functional changes in the skin include a decreased inflammatory response; increased time for wound healing; thinning of the skin, resulting in increased fragility and risk of injury; decreased sweat capacity; and increased dryness secondary to reduced sebum production.3 Formulation of a differential diagnosis for skin lesions is based on an in-depth knowledge of various common skin disorders and their characteristic physical properties, including location and morphologic appearance. In addition, knowledge of the associated history typical of common rashes is essential. Variations in color, texture, and continuity of a patient’s skin may be a normal genetic or ethnic variant, an indicator of a local skin pathologic condition, or an indicator of an underlying systemic disease process. A proper assessment forms the basis for an appropriate care plan, patient education for self-care of acute and chronic skin lesions, and prevention of recurrence. Assessment begins with a careful history and physical examination of basic features, including skin turgor, pigmentation, and degree of photodamage to sun-exposed surfaces.2 Additional investigative techniques, such as Wood light examination, laboratory data, and microscopic skin scraping examination, may be necessary to ensure a definitive diagnosis. Subjective components of a dermatologic history include taking a history from the patient or caregiver regarding the onset and progression of the rash, associated symptoms, any prior skin disorder, medications, travel history, lesions in close contacts, social and occupational factors, and dietary practices. The health care provider inquires about self-care practices, such as homeopathic remedies, lotions, soaps, any change in laundry products, new clothing or fabrics, use of rubber gloves, cosmetics, sunbathing, tanning salons, and the humidity of the patient’s typical ambient environment. In addition, a family history or self-history of skin disorders, allergy, atopy, asthma, or eczema in childhood is reviewed.
Examination of the Skin and Approach to Diagnosis of Skin Disorders
Definition and Epidemiology
Overview of Skin Function, Anatomy, and Structures
Changes in the Skin Associated with Aging
Assessment
History
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Examination of the Skin and Approach to Diagnosis of Skin Disorders
Chapter 38
