Dermatologic Disorders - Merck Manuals Professional Edition

Approach to the Dermatologic Patient

History and physical examination are adequate for diagnosing many skin lesions. Some require biopsy or other testing.
Principles of Topical Dermatologic Therapy

Topical dermatologic treatments are grouped according to their therapeutic functions and include
- Principles of Topical Dermatologic Therapy
Acne and Related Disorders

Acne vulgaris is the formation of comedones, papules, pustules, nodules, and/or cysts as a result of obstruction and inflammation of pilosebaceous units (hair follicles and their accompanying sebaceous gland). Acne develops on the face and upper trunk. It most often affects adolescents. Diagnosis is by examination. Treatment, based on severity, can involve a variety of topical and systemic agents directed at reducing sebum production, comedone formation, inflammation, and bacterial counts and at normalizing keratinization.
Bacterial Skin Infections

Bacterial skin infections can be classified as skin and soft-tissue infections (SSTI) and acute bacterial skin and skin structure infections (ABSSSI).
Benign Skin Tumors, Growths, and Vascular Lesions

Epidermal inclusion cysts are the most common cutaneous cysts. Milia are small epidermal inclusion cysts. Pilar cysts are usually on the scalp and may be familial.
Bullous Diseases

Bullae are elevated, fluid-filled blisters ≥ 10 mm in diameter.
Cancers of the Skin

Skin cancer is the most common type of cancer and commonly develops in sun-exposed areas of skin. The incidence is highest among outdoor workers, sportsmen, and sunbathers and is inversely related to the amount of melanin skin pigmentation; fair-skinned people are most susceptible. Skin cancers may also develop years after therapeutic x-rays or exposure to carcinogens (eg, arsenic ingestion).
Cornification Disorders

Calluses and corns are circumscribed areas of hyperkeratosis at a site of intermittent pressure or friction. Calluses are more superficial, cover broader areas of skin, and are usually asymptomatic. Corns are deeper, more focal, and frequently painful. Diagnosis is by appearance. Treatment is with manual abrasion with or without keratolytics. Prevention involves altering biomechanics, such as changing footwear. Rarely, surgery is required.
Dermatitis

The meaning of the word "dermatitis" is inflammation of the skin. However, in clinical dermatology, dermatitis is used to describe a variety of different skin conditions that share the same inflammatory reaction pattern with similar clinical manifestations.
Fungal Skin Infections

Candidiasis is skin and mucous membrane infection with Candida species, most commonly Candida albicans. Infections can occur anywhere and are most common in skinfolds, digital web spaces, genitals, cuticles, and oral mucosa. Symptoms and signs vary by site. Diagnosis is by clinical appearance and/or potassium hydroxide wet mount of skin scrapings. Treatment is with drying agents and antifungals.
Hair Disorders

Alopecia is defined as loss of hair from the body. Hair loss is often a cause of great concern to the patient for cosmetic and psychologic reasons, but it can also be an important sign of systemic disease.
Hypersensitivity and Reactive Skin Disorders

The immune system plays a significant role in most skin disorders. The following skin disorders can be primarily characterized by a hypersensitivity or other type of reaction, be it to a drug, infection, or cancer:
Nail Disorders

A variety of disorders can affect nails, including deformities, trauma, infections of the nail, paronychia, retronychia, and ingrown toenails. Nail changes may occur in many systemic conditions and genetic syndromes or result from trauma.
Parasitic Skin Infections

Bedbug bites are usually painless but cause reactions, often pruritic, in susceptible patients. Diagnosis is clinical. Treament is symptomatic treatment of bites and chemical and physical eradication of bedbugs.
Pigmentation Disorders

Melanin is the brownish pigment responsible for the color of skin, hair, and the iris of the eyes. It is produced by melanocytes. Most people have similar numbers of melanocytes, and the wide range of color shades of human skin is due to the amount of melanin that is produced rather than the number of melanocytes. There are different subtypes of melanin, the main ones in the skin being
Pressure Injury

Pressure injuries are areas of necrosis and often ulceration (also called pressure ulcers) where soft tissues are compressed between bony prominences and external hard surfaces. They are caused by unrelieved mechanical pressure in combination with friction, shearing forces, and moisture. Risk factors include age > 65, impaired circulation and tissue perfusion, immobilization, undernutrition, decreased sensation, and incontinence. Severity ranges from nonblanchable skin erythema to full-thickness skin loss with extensive soft-tissue necrosis. Diagnosis is clinical. Treatment includes pressure reduction, avoidance of friction and shearing forces, and diligent wound care. Advanced treatments, including negative-pressure wound therapy, cellular and tissue-based products, and surgical intervention, are sometimes needed. Prognosis is excellent for early-stage injuries; neglected and late-stage injuries pose risk of serious infection and are difficult to heal.
- Pressure Injuries
Psoriasis and Scaling Diseases

Psoriasis is an inflammatory disease that manifests most commonly as well-circumscribed, erythematous papules and plaques covered with silvery scales. Multiple factors contribute, including genetics. Common triggers include trauma, infection, and certain medications. Symptoms are usually minimal, but mild to severe itching may occur. Cosmetic implications may be major. Some people also develop psoriatic arthritis. Diagnosis is based on appearance and distribution of lesions. Treatment can include topical treatments (eg, corticosteroids, vitamin D3 analogs, calcineurin inhibitors, tazarotene, roflumilast, tapinarof, emollients, salicylic acid, coal tar, anthralin), phototherapy, and, when severe, systemic medications (eg, methotrexate, oral retinoids, cyclosporine, other immunosuppressants [biologics or small molecules]).
Reactions to Sunlight

The skin may respond to sunlight with chronic (eg, dermatoheliosis [photoaging], actinic keratosis) or acute (eg, photosensitivity, sunburn) changes.
Sweating Disorders

There are two types of sweat glands: apocrine and eccrine.
Viral Skin Diseases

Molluscum contagiosum is characterized by clusters of pink, dome-shaped, smooth, waxy, or pearly and umbilicated papules 2 to 5 mm in diameter caused by molluscum contagiosum virus, a poxvirus. Diagnosis is based on clinical appearance. Treatment is aimed at preventing spread or removing cosmetically unacceptable lesions and can include mechanical methods (eg, curettage, cryosurgery) and topical irritants (eg, cantharidin, tretinoin).