Although skin lesions may represent only a dermatologic disorder, the skin often serves as a marker for underlying internal disease, such as internal cancers, endocrinopathies, and GI disorders. Although the history and physical examination are often adequate for diagnosing many skin lesions, good clinical acumen is essential and diagnostic tests are sometimes needed.
Dermatologic Disorders Sections (A-Z)
Acne and Related Disorders
Acne vulgaris (acne) 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.
Approach to the Dermatologic Patient
Bacterial Skin Infections
Benign Skin Tumors, Growths, and Vascular Lesions
Bullae are elevated, fluid-filled blisters ≥ 10 mm in diameter. Bullous diseases include bullous pemphigoid, dermatitis herpetiformis, epidermolysis bullosa acquisita, herpes gestationis (pemphigoid gestationis—see Pemphigoid Gestationis), linear IgA disease, pemphigus vulgaris, pemphigus foliaceus, staphylococcal scalded skin syndrome (see Staphylococcal Scalded Skin Syndrome), toxic epidermal necrolysis (see Stevens-Johnson Syndrome (SJS) and Toxic Epidermal Necrolysis (TEN)), severe cellulitis, and certain drug eruptions. Mucous membrane pemphigoid (sometimes called benign mucous membrane pemphigoid) is a heterogeneous group of disorders that tends to cause waxing and waning bullous lesions that affect the mucous membranes, often with subsequent scarring and morbidity.
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).
Fungal Skin Infections
Candidiasis (moniliasis) is skin infection with Candida sp, 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 potassium hydroxide wet mount of skin scrapings. Treatment is with drying agents and antifungals.
Hypersensitivity and Inflammatory Disorders
The immune system plays a significant role in a large number of skin disorders, including dermatitis, sunlight reactions, and bullous diseases. Although all of these disorders involve some level of inflammation, certain skin disorders are primarily characterized by their inflammatory component or as a hypersensitivity reaction, be it to a drug, infection, or cancer.
A variety of disorders can affect nails, including deformities, infections of the nail, paronychia, and ingrown toenails (see Ingrown Toenail). Nail changes may occur in many systemic conditions and genetic syndromes or result from trauma.
Parasitic Skin Infections
Parasitic skin infections can cause severe itching and be distressing. Most skin parasites are insects (see Cutaneous Myiasis, Bedbugs, and Lice), mites (see Scabies), or worms (see Cutaneous Larva Migrans) that burrow into the skin for part or all of their life cycle. Also, some systemic parasitic infections have cutaneous manifestations; these include nematodes (eg, ancylostomiasis, dracunculosis, strongyloidiasis, toxocariasis, onchocerciasis—see Introduction to Nematodes) and flukes (eg, schistosomiasis—see Schistosomiasis). Very rarely, patients have delusional parasitosis, in which no parasites are present, but patients are convinced they are infested (see Delusional Parasitosis).
Pressure ulcers (PUs) are areas of necrosis and ulceration where tissues are compressed between bony prominences and hard surfaces. They are caused by pressure in combination with friction, shearing forces, and moisture. Risk factors include age > 65, impaired circulation, immobilization, undernutrition, and incontinence. Severity ranges from nonblanchable skin erythema to full-thickness skin loss with extensive soft-tissue necrosis. Diagnosis is clinical. Prognosis is excellent for early-stage ulcers; neglected and late-stage ulcers pose risk of serious infection and are difficult to heal. Treatment includes pressure reduction, avoidance of friction and shearing forces, and diligent wound care. Sometimes, skin grafts or myocutaneous flaps are needed to facilitate healing.
Principles of Topical Dermatologic Therapy
Psoriasis and Scaling Diseases
Psoriasis (see Psoriasis), parapsoriasis (see Parapsoriasis), pityriasis rosea (see Pityriasis Rosea), pityriasis rubra pilaris (see Pityriasis Rubra Pilaris), pityriasis lichenoides (see Pityriasis Lichenoides), lichen planus (see Lichen Planus), and lichen sclerosus (see Lichen Sclerosus) are dissimilar disorders grouped together because their primary lesions have similar morphologic characteristics: sharply marginated, scaling papules or plaques without exudates, crusts, or fissures. Lesion appearance and distribution distinguish these diseases from each other.
Reactions to Sunlight
Viral Skin Diseases
Many systemic viral infections cause skin lesions. Molluscum contagiosum and warts are the 2 most common primary viral skin diseases without systemic manifestations. For herpes simplex virus infection, see Overview of Herpesvirus Infections.