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Parasitic Infestions

1 Where and how does one acquire cutaneous parasitic diseases? Parasitic skin diseases may arise from systemic spread or direct penetration of the skin. Cutaneous parasitic infestations are a major source of morbidity, affecting millions worldwide. Tropical climates, crowding, poor nutrition, sanitation problems, and limited medical resources are all associated with increased variety and severity of parasitoses. Ecologically temperate climates and industrialized societies are also afflicted…

Deep Fungal Infections

Key Points: Deep Fungal Infections 1. Deep fungal infections can be divided into subcutaneous (localized), systemic, and opportunistic categories. 2. Neutropenic patients are particularly at risk for systemic phaeohyphomycosis, aspergillosis, fusariosis, and mucormycosis. 3. Patients with impaired cellular immunity are particularly at risk for disseminated sporotrichosis, histoplasmosis, coccidioidomycosis, penicilliosis, Cryptococcus , and Candida . 4. The differential diagnosis of lymphocutaneous (sporotrichoid) spread includes SLANTS : S…

Superficial Fungal Infections

1 What is a dermatophyte? A dermatophyte is a fungus that has developed the ability to live on the keratin (hair, nails, or skin scale) of animals. Dermatophytes are classed into three genera: Microsporum , Trichophyton , and Epidermophyton. 2 How are superficial fungal infections diagnosed? Superficial fungal infections can usually be suspected clinically, but definitive diagnosis requires the demonstration of fungal pathogens by microscopic examination…

Mycobacterial Infections

Acknowledgment The authors wish to acknowledge the invaluable input of Genevieve L. Egnatios, MD, Karen Warschaw, MD and Loren Golitz, MD, in coauthoring previous editions of this chapter. 1 What is the Runyon Classification system for mycobacteria? The Runyon Classification was created in the 1950s to organize the mycobacteria based on their rate of growth, ability to form pigment, and colony characteristics. 2 What are the…

Sexually Transmitted Diseases

“Know syphilis in all of its manifestations and relations, and all other things clinical will be added unto you.” –Sir William Osler, 1897 1 What causes syphilis? Syphilis is caused by the spirochete Treponema pallidum , ssp. pallidum , which belongs to the order Spirochaetales. T. pallidum ssp. endemicum is a subspecies that causes bejel, or endemic syphilis. Other pathogenic treponemes for humans include T. pallidum…

Bacterial Infections

Staphylococcal infections 1 Which bacterium is the most common cause of skin infections? Staphylococcus aureus . There are two types of S. aureus infections—methicillin-susceptible S. aureus (MSSA) infections and methicillin-resistant S. aureus (MRSA) infections. These two types of infections are differentiated by the classes of antibiotics to which they respond; however, clinically they look identical. 2 What kinds of skin infections does Staphylococcus aureus produce? Impetigo…

Warts and Molluscum Contagiosum

1 What causes warts? Warts are caused by the human papillomavirus (HPV), a nonenveloped double-stranded DNA virus. There are over 200 known HPV types, and over 100 have been totally sequenced. The virus infects basal keratinocytes, resulting in keratinocyte hyperproliferation. 2 Do any warts come from toads? No. There is no supportive scientific evidence—histologic, viral, or other—that the bumps on the skin of a toad are…

Bullous Viral Eruptions

1 What do herpes simplex virus (HSV) and varicella-zoster virus (VZV) have in common? HSV-1, HSV-2, and VZV are all members of the human herpesvirus family. Other members of this family include cytomegalovirus, Epstein-Barr virus, human herpesvirus-6, human herpesvirus-7, and human herpesvirus-8. The human herpesviruses all contain double-stranded DNA, share certain structural features and mechanisms for infection and replication, and have the capacity to establish latent…

Viral Exanthems

1 What is the difference between an exanthem and an enanthem? Any skin rash that appears abruptly and affects several areas of the body simultaneously is called an exanthem, from the Greek origin “ exanthema ,” which means “ breaking out .” If the rash occurs on mucosal surfaces, it is called an enanthem. 2 Which viruses cause exanthems? Of the hundreds of viruses that infect…

Urticaria and Angioedema

1 What percentage of the population experiences acute urticaria during their lifetime? An estimated 15% to 25% of the population will experience at least one episode of urticaria during their lifetime ( Fig. 23.1 ). 2 How is acute versus chronic urticaria defined? Classification of urticaria begins with duration and frequency of the wheals. Although arbitrary, 6 weeks of nearly daily symptoms has been chosen as…

Autoimmune Connective Tissue Diseases

1 Discuss the skin changes of lupus erythematosus Skin changes occur in about 855 of patients with lupus erythematosus (LE) and in this condition are second in frequency only to musculoskeletal complaints. Skin eruptions in LE may be categorized based upon diagnostic and prognostic significance. Skin lesions diagnostic of LE are called “lupus-specific eruptions.” On biopsy, such lesions show characteristic histopathologic changes of cutaneous LE. In…

Acne and Acneiform Eruptions

Key Points: Acne 1. In acne, the pilosebaceous unit is the target of disease. The microcomedone is the earliest lesion. 2. Combination therapy including a retinoid plus benzoyl peroxide or an antimicrobial agent is the preferred approach for almost all patients with acne. A topical keratolytic (benzoyl peroxide or topical retinoids) should always be used with a topical or oral antibiotic in treating inflammatory acne. 3.…

Alopecia

1 How is alopecia classified? Alopecia (hair loss) can be divided into (1) disorders of the hair shaft and (2) all other forms of hair loss. Abnormalities of the hair shaft can produce alopecia because the shafts are fragile and “break off.” The other forms of alopecia can be divided into cicatricial (scarring) and noncicatricial alopecia. In cicatricial alopecia, hair is lost permanently. In noncicatricial alopecia,…

Panniculitis

Acknowledgments The author wishes to acknowledge the contribution of prior authors, Melissa D. Darling, MD, and James W. Patterson, MD Key Points: Panniculitis 1. Given the similar clinical appearance among panniculitides, histopathologic characterization is often critical for a correct diagnosis. 2. An incisional biopsy with a wide base in the fat is far more likely to be diagnostic than a deep shave or punch biopsy. 3.…

Disorders of Pigmentation

1 Are some disorders of pigmentation markers for systemic disease? Yes. Examples include the following: Generalized depigmentation: Albinism. Generalized hyperpigmentation: Addison's disease. Ash-leaf hypopigmented macules: Tuberous sclerosis. Axillary and inguinal freckles: Neurofibromatosis. Lentigines: Peutz-Jeghers syndrome. 2 How do you diagnose a pigmentation disorder? The clinical history is the most important aspect when considering a pigmentation disorder. It should focus on the time of onset (such as…

Photosensitive Dermatitis

1 What is “photosensitivity”? Photosensitivity is defined as development or exacerbation of a skin eruption and/or skin symptoms (such as pruritus or pain) after exposure to light (particularly to sunlight, but possibly due to an artificial light source of similar wavelength). Admittedly, the patient may not always directly relate an eruption to light exposure, and there may also be a delay in the onset of signs…

Deposition Disorders

Acknowledgments The author wishes to acknowledge the contributions of the previous authors, Lisa E. Maier, MD, and Lori Lowe, MD. Key Points: Cutaneous Deposition Disorders 1. Amyloid deposition can result in both localized and systemic disease. 2. Pretibial myxedema is associated with Graves' disease. 3. The porphyrias are a group of diseases caused by defects in heme biosynthesis–related enzymes. 4. Lesions of lichen myxedematosus result from…

Vasculitis

1 How are vasculitic disorders defined and classified? Vasculitis is defined as inflammation of blood vessels. Vasculitis may be confined to the skin; however, the majority of cases of cutaneous vasculitis are part of multisystemic disorders that in addition to involving skin also involve other organ systems. Classification is problematic due to the lack of standardization and definition. The most accepted classification scheme for systemic vasculitis…

Drug Eruptions

1 A patient presents to your office with a 10-page typed-out medical history. She states that she is “allergic” to 20 different medicines. Is she likely to have drug allergies or drug intolerances to most of these drugs? Drug intolerances account for 90% of adverse drug reactions. An adverse reaction to a drug is an undesirable and usually unanticipated response independent of the intended therapeutic purpose…

Granulomatous Diseases of the Skin

1 What is meant by “granulomatous diseases of the skin”? Granulomatous disorders of the skin comprise a broad category of diseases that are characterized by the accumulation of activated macrophages with an epithelioid appearance in the dermis or subcutaneous tissue. A granuloma is a distinct aggregate composed of epithelioid macrophages with or without multinucleated giant cells. These aggregates are typically surrounded by a rim of lymphocytes…