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Lichenoid Skin Eruptions

1 How do lichenoid eruptions differ from other papulosquamous conditions? Lichenoid skin eruptions are a subcategory of papulosquamous skin disease. While most papulosquamous eruptions present with scaling papules, lichenoid eruptions differ in that the scale is often subtle, and the papules tend to remain small and discrete. On occasion, confluent plaques may form. 2 What does “lichenoid” mean? The term lichenoid has at least three commonly…

Pustular Eruptions

1 How does a pustule differ from a vesicle or bulla? A pustule is a purulent vesicle or bulla. Whereas a vesicle contains clear or translucent fluid, a pustule is filled with neutrophils or, less commonly, eosinophils. Pustules are one of the primary lesions in skin. Most pustular eruptions begin as pustules, but others may pass through a transitory stage in which they appear vesicular (vesiculopustules).…

Vesiculobullous Disorders

1 What is the difference between a vesicle and a bulla? Size. If a blister is less than 5 mm in diameter, it is referred to as a vesicle. If a blister is 5 mm or larger, it is called a bulla. Some dermatologists require bulla be 1 cm or larger. The term “vesiculobullous” may be used for blistering disorders, as it encompasses blisters of varying…

Contact Dermatitis

1 Name the two pathogenic types of contact dermatitis Contact dermatitis refers to cutaneous inflammation resulting from the interaction of an external agent and the skin. These reactions occur through one of two mechanisms: a nonimmunologic irritant contact dermatitis (ICD) or an immunologic allergic contact dermatitis (ACD). ICD accounts for 80% of all reactions, while ACD is responsible for approximately 20%. Although over 3700 substances have…

Eczematous Dermatitis

1 What is eczematous dermatitis? Eczematous dermatitis is the clinical diagnosis used to designate a broad category of skin disorders that manifest with intensely pruritic, scaly, erythematous macules, papules, vesicles, or plaques, often with poorly defined margins. The base term eczema is taken from the Greek ekzema meaning “to boil over.” Eczema tends to have overlapping clinical phases: acute (vesicular), subacute (scaling and crusting), and chronic…

Papulosquamous Skin Eruptions

1 Name the papulosquamous skin eruptions Papulosquamous skin disorders are inflammatory reactions characterized by red or purple papules and plaques with scale. These diseases include psoriasis, pityriasis rubra pilaris (PRP), seborrheic dermatitis, pityriasis rosea, and pityriasis lichenoides et varioliformis acuta (PLEVA). Lichen planus and lichen nitidus are also considered papulosquamous disorders (see Chapter 12). 2 What is psoriasis? Psoriasis is a common, genetically determined, inflammatory, and…

Mechanobullous Disorders

Acknowledgment The author acknowledges the prior contributions of Drs. H. Alan Arbuckle and Ronald E. Grimwood to this chapter. 1 What are mechanobullous disorders? Mechanobullous disorders, either inherited or acquired, are skin conditions characterized by blister formation (vesicles, bullae, and resultant erosions) due to mechanical trauma to the skin and/or mucous membranes. Common friction blisters that develop on the feet due to tight-fitting shoes or boots…

Neurocutaneous Disorders

Acknowledgment Some of the clinical photographs were kindly provided by Drs. William Weston and Joseph Morelli. Neurofibromatosis 1 What are the two main forms of neurofibromatosis? Neurofibromatosis type 1 (NF-1 or von Recklinghausen's disease) and neurofibromatosis type 2 (NF-2). NF-1 accounts for 90% of all cases of neurofibromatosis and affects approximately 1 in 2600–3000 individuals. NF-2 is a genetically distinct entity with a prevalence of 1…

Disorders of Keratinization

1 What are the ichthyosiform dermatoses? The ichthyosiform dermatoses are a heterogeneous group of disorders presenting with excessive scaling of the skin. The inherited forms of the ichthyoses are most common, although the condition can occur secondary to other diseases. 2 What does “ichthyosis” mean? The term ichthyosis is derived from the Greek root ichthy, meaning fish, indicative of the scales on the skin of affected…

Diagnostic Techniques

1 What is the most sensitive office laboratory test for diagnosing dermatophyte infections of the skin? Microscopic examination of a potassium hydroxide (KOH) preparation of scrapings taken from the affected area is the most sensitive office laboratory test. A study of 220 specimens examined by both KOH and culture demonstrated positive KOH preparations and positive cultures in 45% of samples, a positive KOH preparation and negative…

Morphology of Primary and Secondary Skin Lesions

1 Why do dermatologists use words that no one else understands? The language of dermatology is unique. It encompasses terms that rarely, if ever, are used in other medical specialties. The use of these correct dermatologic terms is important to accurately describe skin lesions to dermatologists during telephone calls and during rounds and teaching. A good description of a skin lesion enables the listener to formulate…

Structure and Function of the Skin

Key Points: Anatomy and Function of Skin 1. The skin is composed of an epidermis, dermis, and subcutis (composed mainly of subcutaneous fat). 2. The four primary functions of skin are: Barrier function and prevention of desiccation Immune surveillance Temperature control Cutaneous sensation 3. The main cell types in the epidermis are melanocytes, keratinocytes, Langerhans cells, and Merkel cells. 4. Genetic mutations in critical adhesion molecules…

Ulcers

Diabetic ulcers Diabetic wounds are multifactorial in etiology. Patients with long-standing diabetes develop polyneuropathy, which creates sensory, motor, and proprioceptive abnormalities and can lead to insensate skin and foot deformities. Combined with vascular disease and immunosuppression, patients have a high risk for trauma, subsequent ulceration, and infection. Most diabetic foot ulcers (DFUs) result from peripheral neuropathy (60%–70%), peripheral vascular disease (15%–20%), or a combination of both…

Dermatoses of pregnancy

Introduction There are four accepted entities included in the dermatoses of pregnancy. They are pemphigoid gestationis (PG; also known as “herpes gestationis” or “gestational pemphigoid”); polymorphic eruption of pregnancy (PEP; also known as “pruritic urticarial papules and plaques of pregnancy” or “PUPPP”); atopic eruption of pregnancy (AEP); and intrahepatic cholestasis of pregnancy (ICP; also known as “obstetric cholestasis” or “jaundice of pregnancy”). Nomenclature in this group…

Drug reactions with systemic symptoms

Acute generalized exanthematous pustulosis Clinical features Acute generalized exanthematous pustulosis (AGEP) is an uncommon, severe cutaneous eruption that is attributed to drugs in more than 90% of cases ( Fig. 18.1 ). It is characterized by the rapid development of numerous superficial sterile pustules on an erythematous base. It has an estimated incidence of 1 to 5 cases per million per year. AGEP commonly affects adults…

Drug rashes

Morbilliform drug eruption Clinical features Morbilliform drug eruption, also called “exanthematous” or “maculopapular drug eruption,” is the most common form of cutaneous drug eruption, accounting for more than 80% of drug eruptions. The term “morbilliform” is often used to describe this condition because the morphology and distribution of the rash looks similar to those of viral exanthems (i.e., measles). Morbilliform drug eruption is considered to be…

Multiple nails

Onychomycosis Douglas Albreski Clinical features A fungal infection of the nail, referred to as “onychomycosis” or “tinea unguium,” is an infection of the nail in which the organism changes the structure and shape of the nail plate, leading to thickening, changes in appearance, and/or discoloration. Changes in appearance are dependent on the organism and site of infection. There are five common types of onychomycosis. Distal dystrophic…

Conditions that frequently affect a single nail

Melanonychia Brett Sloan Clinical features Melanonychia is dark brown or black pigmentation on the nail plate. There are numerous causes, the most concerning being melanoma of the nail unit. Melanonychia can present as diffuse darkening of the nail plate or, more commonly, as a longitudinal line, which is known as “longitudinal melanonychia” (LM). Melanonychia is a misnomer because the nail pigmentation is not necessarily the result…

Focal hair loss

Alopecia areata Rana Abdat Clinical features Alopecia areata (AA) is a common cause of hair loss that affects men and women equally and can affect patients of all ages. AA is the second most common cause of nonscarring hair loss after androgenetic alopecia (AGA; also known as “male/female pattern hair loss”). It is of unclear etiology but is thought to be immune mediated via loss of…

Diffuse hair loss

Androgenetic alopecia Clinical features Androgenetic alopecia (AGA; also known as “female-pattern hair loss” and “male-pattern baldness”) is the most common type of hair loss in both men and women. It is caused by androgen-mediated effects on hair follicles, which result in miniaturization of hairs, decreased hair count, and observable hair thinning in a male-patterned scalp distribution. AGA presents differently in men and women and treatment differs,…