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Bacterial Diseases

Key features ▪ Roughly 20% of outpatient dermatology visits are for bacterial skin infections ▪ Staphylococci and streptococci cause the majority of bacterial skin conditions, which range from common infections (e.g. impetigo) to multisystem disorders (e.g. toxic shock syndrome) ▪ An increase in the prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) remains a concern ▪ Various systemic diseases and immunodeficiency states predispose patients to bacterial skin…

Anogenital (Non-venereal) Disease

Introduction The diagnosis and management of skin diseases in the anogenital region may be complex. The juxtaposition of urinary, genital and alimentary tracts gives rise to special considerations at this site ( Fig. 73.1 ), and disease of any of these major systems may present with cutaneous manifestations. A number of systemic diseases such as Crohn disease and zinc deficiency preferentially affect the anogenital area. Local…

Oral Disease

Introduction From both a clinical and histologic standpoint, the oral cavity is an amazingly diverse anatomic region. This is not surprising when one considers the various tasks and environmental interactions that take place within the mouth. Sites that are associated with the friction of mastication, such as the hard palate and attached gingivae, are bound to underlying periosteum and are referred to as attached mucosa or…

Nail Disorders

Anatomy Key features ▪ Nail matrix → nail plate production proximal matrix → dorsal nail plate distal matrix (lunula) → ventral nail plate ▪ Proximal nail fold → nail matrix protection ▪ Nail bed and hyponychium → nail plate adhesion and distal detachment ▪ Nail growth rate: fingernails: 3 mm/month; toenails: 1 mm/month The nail plate is a fully keratinized structure produced by the germinative epithelium of the…

Hypertrichosis and Hirsutism

Key features ▪ Hypertrichosis refers to excessive growth of hair anywhere on the body, whereas hirsutism represents excessive hair growth within androgen-dependent sites in girls and women ▪ Hypertrichosis may be generalized or localized, with etiologies ranging from genodermatoses to underlying hamartomas to repeated trauma ▪ Hirsutism is related to hormonal factors, in particular an increase in circulating androgen levels and/or enhanced sensitivity of hair follicles…

Alopecias

Introduction In this chapter, the major non-cicatricial (non-permanent) alopecias will be reviewed first, followed by a discussion of cicatricial alopecias and a review of structural hair shaft abnormalities. Chapter 68 reviews the structure and function of the hair follicle as well as regulation of the hair cycle. Table 69.1 outlines the historical information of importance in the evaluation of alopecias while Figs 69.1 and 69.2 depict…

Biology of Hair and Nails

Key features ▪ The pilosebaceous unit and nail apparatus are epidermal derivatives that produce two of the hardest epithelial structures in mammalian biology ▪ The hair follicle is the only continuously cycling organ in mammals, while the nail exhibits uninterrupted growth ▪ Hair and nails serve multiple functions, including protection, sensation, and social communication ▪ Hair shafts and nail plates largely consist of dead, terminally differentiated…

Disorders of Hyperpigmentation

Skin color depends upon the amount and distribution of melanin and other pigments such as hemoglobin, which can influence light absorption, reflection, and scattering. Disorders of hyperpigmentation usually result from an increase in melanin production and, on occasion, from an increase in the density of active melanocytes. Discoloration of the skin may also be caused by deposition of exogenous substances such as drugs, drug complexes (e.g.…

Vitiligo and Other Disorders of Hypopigmentation

Key features ▪ Leukoderma and hypopigmentation refer to lightening of the skin, which is classically due to decreased epidermal melanin (hypomelanosis) ▪ Melanocytopenic hypomelanosis, characterized by a reduction in the number of melanocytes, can result from a variety of defects in pigment cell differentiation, proliferation, migration, and/or survival ▪ Melanopenic hypomelanosis features a normal number of melanocytes but decreased melanin synthesis or transfer to keratinocytes, and…

Melanocyte Biology

Key features ▪ The major determinant of normal skin color is the activity of melanocytes, i.e. the quantity and quality of pigment production, not the density of melanocytes ▪ Melanocytes contain a unique intracytoplasmic organelle, the melanosome, which is the site of melanin synthesis and deposition ▪ Compared with lightly pigmented skin, darkly pigmented skin has melanosomes that contain more melanin and are larger; once transferred…

Developmental Anomalies

Key features ▪ The human neural tube is thought to close in an intermittent, multisite pattern, and neural tube defects that present as midline cutaneous lesions (e.g. cephaloceles, heterotopic brain tissue, rudimentary meningoceles) typically occur at the junction between two closure sites ▪ Midline lesions of the nose and scalp have a high likelihood of representing developmental defects with a potential intracranial connection, and an evaluation…

Other Genodermatoses

Introduction In this chapter, a number of genodermatoses are discussed that are not covered in other chapters of this textbook ( Table 63.1 ). Table 63.1 Genodermatoses. See also Chapter 55 . GENODERMATOSES Hereditary connective tissue disorders ( Chs 64 , 95 , 97 , 98 ) Disorders of keratinization ( Chs 57 , 58 , 59 ) Hereditary epidermolysis bullosa ( Ch. 32 ) Hereditary…

Mosaicism and Linear Lesions

Key features ▪ Mosaicism for genes expressed in the skin presents as a patchy distribution of affected and unaffected skin ▪ The classical pattern follows the lines of Blaschko but varies according to cell type and timing of mosaicism ▪ Epidermal and vascular nevi represent mosaicism for a variety of genes with corresponding associated features ▪ Some linear disorders are recognizable as localized forms of autosomal…

Neurofibromatosis and Tuberous Sclerosis Complex

Introduction Neurofibromatosis (NF) and tuberous sclerosis (TS) are neurocutaneous disorders, or phakomatoses. They are characterized by cutaneous lesions as well as peripheral and/or central nervous system neoplasms. Like most hereditary cancer syndromes, NF and TS are autosomal dominant in inheritance. Despite a high penetrance for both diseases, new cases of NF type 1 (NF1) and TS frequently represent de novo mutations. The pleiotropic nature of these…

Primary Immunodeficiencies

Introduction Primary immunodeficiencies represent a heterogeneous group of inherited disorders characterized by immune system defects that result in susceptibility to infections as well as additional manifestations such as autoimmunity, allergy, and malignancy. The molecular bases have been defined for >200 monogenic primary immunodeficiency diseases, providing valuable insight into the functions of the human immune system . Patients with genetic immunodeficiency disorders often manifest with cutaneous abnormalities…

Darier Disease and Hailey–Hailey Disease

Darier Disease Synonyms ▪ Darier–White disease ▪ Keratosis follicularis ▪ Dyskeratosis follicularis Key features ▪ Autosomal dominant disorder in which mutations in the ATP2A2 gene result in dysfunction of an endoplasmic reticulum Ca 2+ ATPase (SERCA2), thus interfering with intracellular Ca 2+ signaling ▪ Keratotic and crusted papules and plaques favor seborrheic areas; additional features include palmoplantar papules, variable nail changes, and whitish oral mucosal papules…

Palmoplantar Keratodermas

Key features ▪ Palmoplantar keratodermas can be inherited or acquired ▪ The three major patterns of involvement are diffuse, focal, and punctate ▪ The clinical presentation may be different on the hands and feet, e.g. diffuse on the soles and focal on the palms ▪ Additional distinguishing features include an erythematous border, transmigration to areas beyond the palmoplantar skin, and digital constrictions (pseudoainhum) ▪ Patients may…

Ichthyoses, Erythrokeratodermas, and Related Disorders

Key features ▪ Ichthyoses and erythrokeratodermas are heterogeneous groups of disorders of cornification ▪ Ichthyoses are characterized by scaling of the skin in a widespread distribution ▪ Erythrokeratodermas feature discrete areas of erythema and hyperkeratosis, usually without substantial scale ▪ Most inherited ichthyoses and erythrokeratodermas are evident at birth or manifest in infancy ▪ Clinical features and pattern of inheritance as well as the underlying structural,…

Biology of Keratinocytes

Key features ▪ The epidermis functions as a barrier that provides protection against harmful substances and water loss ▪ Through a complex terminal differentiation program, the progeny of epidermal stem cells undergo molecular and biochemical changes that generate the morphologically different strata of the epidermis ▪ Keratinocyte terminal differentiation culminates in the replacement of the plasma membrane with the cornified cell envelope ▪ Keratin intermediate filaments,…

Genetic Basis of Cutaneous Diseases

Key features ▪ Advances in molecular technology have led to elucidation of the genetic bases of many single-gene inherited and mosaic skin disorders, greatly improving our understanding of these conditions ▪ McKusick's Online Mendelian Inheritance in Man (OMIM) database provides easily accessible, up-to-date information on human genes and genetic diseases; each gene or phenotype entry is assigned a specific six-digit MIM number ▪ Genotype–phenotype correlations in…