Porth's Essentials of Pathophysiology, 4e

1157

Disorders of Skin Integrity and Function

C h a p t e r 4 6

FIGURE 46-7. Cellulitis on leg infected with Staphylococcus aureus and Pseudomonas.

(Bactroban), which has few side effects, may be effective for limited infections. If the area is large or if there is concern about complications, systemic antibiot- ics are used. Another form of impetigo exists, bullous impetigo, which is usually caused by Staphylococcus aureus . 10 Bullous impetigo is more common among children and occurs intermittently, with some cases transmitted among family members, but most often found among the institutionalized. Thin bullae erupt that appear clear to cloudy and coalesce. The bullae open, leaving the original bullous rim with central thin, flat, honey- colored crusts, or in some cases denuded areas. The face is often affected, but bullous impetigo may occur anywhere on the body. The treatment measures are the same as for nonbullous impetigo. Cellulitis. Cellulitis is a deeper infection affecting the dermis and subcutaneous tissues. 11 It is usually caused by group A β -hemolytic streptococci or S. aureus, but can be caused by bacteria specific to certain activities, such as fish handling, swimming in fresh or salt water, or from animal bites or scratches. Preexisting wounds (e.g., ulcers, erosions) and tinea pedis are often portals of entry. Legs are the most common sites, followed by the hands and pinnae of the ears, but cellulitis may occur on many body sites. The lesion consists of an expanding red, swollen, tender plaque with an indefinite border, covering a variety of widths (Fig. 46-7). Cellulitis is fre- quently accompanied by fever, erythema, heat, edema, and pain. Cellulitis often involves the lymph system and, once compromised, repeat infections may impair lym- phatic drainage, leading to chronically swollen legs, and eventually dermal fibrosis and lymphedema. Incorrectly treated, it may result in septicemia, nephritis, or death. Treatment measures (oral and intravenous antibiotics) are aimed at the invasive organisms and the extent of the infection. FIGURE 46-6. The lesions on this patient’s forearm proved to be a dermatological condition caused by Staphylococcus aureus bacteria. Note the blister-like rash and the crusted lesion that resulted from the golden brown discharge as it dried. (From the Centers for Disease Control and Prevention Public Health Image Library. No. 14927. Courtesy of Dr. Herman Miranda, Univ. of Trujello, Peru; A. Chambers.)

Viral Infections Viruses are intracellular pathogens that rely on live cells of the host for reproduction. They have no organized cell structure but consist of a deoxyribonucleic acid (DNA) or ribonucleic acid (RNA) core surrounded by a protein coat. The viruses seen in dermatoses tend to con- tain DNA. They invade the keratinocyte, begin to repro- duce, and cause cellular proliferation or cellular death. The incidence of viral dermatoses is increasing. This has been attributed to the use of corticosteroid drugs, which have immunosuppressive properties, and the use of anti- biotics, which alter the bacterial flora of the skin. As the number of bacterial infections has decreased, there has been a proportional rise in viral skin diseases. Verrucae. Verrucae, or warts, are common benign pap- illomas caused by the DNA-containing human papillo- mavirus (HPV). 12 As benign papillomas, warts represent an exaggeration of the normal skin structures. There is an irregular thickening of the stratum spinosum and greatly increased thickening of the stratum corneum. The classification of warts is based largely on morphol- ogy and location. Although warts vary in appearance depending on their location, it is now recognized that the clinically distinct types of warts result not simply because of the anatomic sites in which they arise, but also because of the distinct type of HPV. There are more than 80 types of HPV found on the skin and mucous membranes of humans that cause several different kinds of warts, including skin warts and genital warts. Many of the HPV types that cause genital warts are sexually transmitted, some of which (types 6, 11, 16, and 18) may increase the risk of cervical cancer (discussed in Chapter 41). Nongenital warts often occur on the hands and feet. They are commonly caused by HPV types 1, 2, 3, 4, 27, and 57, and are not considered precancerous lesions. They are classified as common warts, flat warts, and plantar or palmar warts. Common warts, or verrucae vulgaris, are the most common type. The lesions can occur anywhere, but most frequently occur on dorsal surfaces of the hands, especially the periungual area,