Lesions on the mucous membranes may be more difficult to diagnose than lesions on the skin, and not merely because they are less easily and less often seen. There is less contrast of color and greater likelihood of alterations in the original appearance because of secondary factors, such as maceration from moisture, abrasion from food and teeth, and infection. Vesicles and bullae rapidly rupture to form…

Diseases of the Hair Normal human hairs can be classified according to cyclic phases of growth. Anagen hairs are growing hairs; catagen hairs are those undergoing transition from the growing to the resting stage; and telogen hairs are resting hairs, which remain in the follicles for variable periods before they fall out (teloptosis). The lag period between loss of the telogen hair and growth of a…

Cutaneous Lymphoid Hyperplasia (Lymphocytoma Cutis, Lymphadenosis Benigna Cutis, Pseudolymphoma) Benign cutaneous lymphoid hyperplasia can be caused by medications, injected foreign substances, infections, and arthropod bites, or it may be idiopathic. If there is a histologic resemblance to lymphoma, the term pseudolymphoma is often used. By standard techniques, most cases of cutaneous lymphoid hyperplasia will be found to lack clonality. Cases of monoclonal B-cell and T-cell cutaneous…

Granulatomatous reactions generally represent patterns of chronic inflammation that may take a long time to develop and a long time to respond to treatment. Granulomatous inflammation can occur in the setting of inflammatory disorders (autoimmune, autoinflammatory), medication reactions, malignancies, and infections. Palisaded Granulomatous Dermatoses Granuloma Annulare Granuloma annulare (GA) is a relatively common idiopathic disorder of the dermis and subcutaneous tissue. It occurs in all races…

Melanocytes originate in the embryonal neural crest and migrate to the epidermis, dermis, leptomeninges, retina, mucous membrane epithelium, inner ear, cochlea, and vestibular system. Nevus cells are a form of melanocyte with a tendency to aggregate into clusters of cells. Nevus cells lack dendritic processes but are otherwise similar to other melanocytes. Epidermal Melanocytic Lesions The melanocytes occurring at the dermoepidermal junction (DEJ) are dendritic cells…

Epidermal Nevi Epidermal nevi are hamartomatous growths of the epidermis that are present at birth in about half of patients or develop early in childhood. The term epidermal nevus includes several entities, including keratinocytic epidermal nevi, nevus sebaceus, and nevus comedonicus, depending on which epidermal cell or structure comprises the lesion. Epidermal nevi of all types are considered an expression of cutaneous mosaicism with genetic mutation…

In this chapter proliferations derived from vascular endothelial cells, fibroblasts, myofibroblasts, smooth muscle cells, Schwann cells, and lipocytes are reviewed. Also discussed are several neoplasms of cells invading or aberrantly present in the dermis, such as metastatic cancer, endometriosis, and meningioma. Cutaneous Vascular Anomalies Vascular anomalies are overgrowths of various types of blood or lymphatic vessels. They can either occur in isolation or as part of…

The genetic basis for common diseases such as atopic dermatitis and psoriasis, in addition to rare diseases, has been partially elucidated. Some genetic disorders are explained by mutations in a specific gene or genes that lead to a specific clinical phenotype that can be recognized based in part on the skin manifestations. These are termed genodermatoses, and recognizing the skin features can lead to earlier diagnosis…

Amyloidosis Amyloid is a material deposited in the skin and other organs that is eosinophilic, homogeneous, and hyaline in appearance. It represents beta-pleated sheet forms of various host-synthesized molecules processed into this configuration by host cells. Amyloidosis can be classified as systemic, localized, and heredofamilial types. The systemic types can deposit amyloid in multiple organs due to an overproduction of a host protein that cannot be…

Collagen Many types of collagen have been identified in tissues of vertebrates ( Table 25.1 ). Collagens help form the support structure and scaffolding for many parts of the body, including tissues, blood vessels, and bones. Fibrillar collagens (types I, II, III, V, and XI) form fibrils that are among the most abundant proteins in the body. Type I collagen accounts for 60%–90% of the dry…

The skin interacts with the endocrine system in many ways. Some of these are discussed in this chapter. Leventhal JS, et al: Skin manifestations of endocrine and neuroendocrine tumors. Semin Oncol 2016; 43: 335. Quatrano NA, et al: Dermatologic manifestations of endocrine disorders. Curr Opin Pediatr 2012; 24: 487. Acromegaly Excess growth hormone (GH) in prepubertal children leads to gigantism, whereas once the epiphyseal growth plates close, such…

An inflammatory disorder that is primarily localized in the subcutaneous fat is termed a panniculitis. This group of disorders may be challenging for both the clinician and the dermatopathologist. Clinically, in all forms of panniculitis, lesions present as subcutaneous nodules. Histopathologically, the subcutaneous fat is a rather homogeneous tissue, and inflammatory processes may show considerable overlap. One way of classifying panniculitis is to separate them into…

A nutritional disease is caused either by insufficiency or, less often, by excess of one or more dietary essentials. Nutritional deficiencies are particularly common in developing countries but can also occur due to fad diets or restrictive eating practices in patients with behavioral or autism spectrum disorders. Infants and children are particularly at risk for deficiency states, especially malnutrition. Infants diagnosed with multiple food allergies who…

In noninherited chronic blistering (vesicular or bullous) dermatoses, the cause of blistering is usually an autoimmune reaction, and the location where antibodies bind determines the clinical, histologic, and immunofluorescent pattern. A thorough understanding of the basement membrane zone (BMZ) structure and location of specific autoantigens and the target proteins of autoantibodies is critical. The desmoglein compensation hypothesis, based on the differential expression of desmoglein 1 and…

The major groups of animals responsible for bites, stings, and parasitic infections in humans belong to the phyla Arthropoda, Chordata, Cnidaria (formerly Coelenterata), Nemathelminthes, Platyhelminthes, Annelida, and Protozoa. This chapter reviews parasitic diseases and the major causes of bites and stings, as well as strategies for prevention. Phylum Protozoa The protozoa are one-celled organisms, divided into classes according to the nature of their locomotion. Class Sarcodina…

Viruses are obligatory intracellular parasites. The structural components of a viral particle (virion) consist of a central core of nucleic acid, a protective protein coat (capsid), and (in certain groups of viruses only) an outermost membrane or envelope. The capsid of the simplest viruses consists of many identical polypeptides (structural units) that fold and interact with one another to form morphologic units (capsomeres). The number of…

Syphilis Syphilis, also known as lues, is a contagious, sexually transmitted disease caused by the spirochete Treponema pallidum subspecies pallidum. The only known host is the human. The spirochete enters through the skin or mucous membranes, where the primary manifestations are seen. In congenital syphilis, the treponeme crosses the placenta and infects the fetus. The risk of acquiring infection from sexual contact with an infected partner…

Epidemiology The World Health Organization (WHO) has committed itself to eliminating Hansen disease as a public health problem, but the disease remains endemic in certain regions, with 95% of cases reported from 16 countries. Brazil, India, and Indonesia account for 80% of all cases worldwide. Although 90% of diagnosed U.S. cases are imported, Hansen disease is endemic in the coastal southeastern United States and in Hawaii.…

Tuberculosis No ideal classification scheme exists for cutaneous tuberculosis (TB), but the system listed here is logical and takes into account the mechanism of disease acquisition. Unfortunately, unlike in Hansen disease, these categories do not correlate perfectly to host immunity. The four major categories of cutaneous TB are as follows: 1 Inoculation from an exogenous source (primary inoculation TB, TB verrucosa cutis) 2 Endogenous cutaneous spread…

Superficial and Deep Mycoses Fungal infections, including dermatophytes and candida, are the most common type of infection worldwide. Cutaneous infections are divided into superficial (those that affect mostly the skin) and deep (those that are typically more invasive) mycoses. In addition immunosuppressed patients are at high risk for opportunistic fungal infections, including from molds and other saprophytic fungi that are not typically pathogens in normal hosts.…