Teresa S. Wright

Viral and Rickettsial Diseases

Viral infection is a major source of cutaneous disease, and skin lesions are frequently biopsied. Viropathic changes help to identify various types of viruses, while in some cases secondary changes, such as keratinocyte dysplasia, identify the offending virus. Viral infections can be limited to the skin, but systemic infection may also give rise to cutaneous manifestations. Rickettsial infections are far less commonly biopsied. Skin involvement is generally associated with systemic disease that is often quite serious.

Dermatoses with Minimal Epidermal Changes

This group of skin disorders is clinically varied but characterized histologically by an inflammatory infiltrate primarily localized to the dermis. Some of the described conditions represent reactive cutaneous processes or phenotypic demonstrations of genetic mutations while others are idiopathic.

Melanocytic Proliferations and Other Pigmented Lesions

This chapter reviews pigmented skin lesions of varied etiology. Some are acquired while others are present at birth or inherited as part of a genetic syndrome.

Muscle and Bone Proliferations

This chapter discusses cutaneous presentations of benign and malignant proliferations of muscle and bone.

Keratinous Cysts and Hamartomas

There are many cysts and hamartomatous growths that present during childhood. The clinical and histologic features of these lesions are described in this chapter, along with discussions of pathogenesis and any associated syndromes.

Insect Bites and Infestations

The skin is susceptible to assault by a range of insects. In some conditions, such as Norwegian scabies, abundant organisms can be readily identified with routine stains. With most insect-induced eruptions, it is unusual to find the actual agent within a skin biopsy; however, characteristic reaction patterns can help to identify various types of insect bites.

Bacterial and Protozoal Diseases

Myriad microorganisms, including bacteria, mycobacteria and protozoa, infect the skin. The skin can be the primary target or secondarily infected as part of a systemic process. In many cases, special stains can be used to identify microorganisms. Other microorganisms can be identified based upon morphology observed with routine stains, although this is unusual with bacterial infections. Attention to the host reaction patterns can provide important clues as to the infecting microorganism.

Inflammatory Disorders of the Cutaneous Appendages

Inflammatory infiltrates centered on eccrine and apocrine structures and pilosebaceous units give rise to a range of cutaneous disorders. These conditions range from alopecia to acne vulgaris to blistering diseases of childhood, all of which have in common a peri-appendageal inflammatory infiltrate. The varying cell types and location of the infiltrates result in a wide range of cutaneous disorders.

Disorders of Pigmentation

Human variability is most strikingly defined by variations in skin and hair color. Skin pigmentation is primarily a result of melanocyte functioning. However, surrounding keratinocytes, extracellular matrix proteins and dermal fibroblasts also play a role in cutaneous homeostasis and the phenotypic demonstration of color.

Diseases of the Hair and Nails

Hair abnormalities can be of considerable psychosocial significance to both children and adults, and can serve as a marker for systemic disease, whether it be inherited or acquired. Similarly, nail changes, such as discoloration or thickening, can represent a local phenomenon (as seen in onychomycosis) or be a herald of general health.