Viruses are obligatory intracellular parasites. The structural components of a viral particle (virion) consist of a central core of nucleic acid, a protective protein coat (capsid), and (in certain groups of viruses only) an outermost membrane or envelope. The capsid…
Syphilis Syphilis, also known as lues, is a contagious, sexually transmitted disease caused by the spirochete Treponema pallidum subspecies pallidum. The only known host is the human. The spirochete enters through the skin or mucous membranes, where the primary manifestations…
Epidemiology The World Health Organization (WHO) has committed itself to eliminating Hansen disease as a public health problem, but the disease remains endemic in certain regions, with 95% of cases reported from 16 countries. Brazil, India, and Indonesia account for…
Tuberculosis No ideal classification scheme exists for cutaneous tuberculosis (TB), but the system listed here is logical and takes into account the mechanism of disease acquisition. Unfortunately, unlike in Hansen disease, these categories do not correlate perfectly to host immunity.…
Superficial and Deep Mycoses Fungal infections, including dermatophytes and candida, are the most common type of infection worldwide. Cutaneous infections are divided into superficial (those that affect mostly the skin) and deep (those that are typically more invasive) mycoses. In…
Bacterial infections in the skin often have distinct morphologic characteristics that should alert the clinician that a potentially treatable and reversible condition exists. These cutaneous signs may be an indication of a generalized systemic process or simply an isolated superficial…
Acne Vulgaris Clinical Features Acne vulgaris is a chronic inflammatory disease of the pilosebaceous follicles, characterized by comedones, papules, pustules, nodules, and often scars. The comedo is the primary lesion of acne. It may be seen as a flat or…
Lichen Planus Lichen planus (LP) is a common, pruritic, inflammatory disease of the skin, mucous membranes, and hair follicles. It occurs throughout the world, in all races. Cutaneous LP affects 0.3% of men and 0.1% of women. Oral LP affects…
Pityriasis Rosea Clinical Features Pityriasis rosea is a mild inflammatory exanthem characterized by salmon-colored thin papules and plaques that are at first discrete but may become confluent ( Fig. 11.1 ). The individual patches are oval or circinate and covered…
Seborrheic Dermatitis Clinical Features Seborrheic dermatitis is common, occurring in 2%–5% of the population. It is a chronic, superficial, inflammatory disease with a predilection for the scalp, eyebrows, eyelids, nasolabial creases, lips, ears ( Fig. 10.1 ), sternal area, axillae,…