Nummular eczema is commonly noted in adults, many of whom also have an atopic predisposition. It may also be seen in children as a clinical variant of atopic dermatitis. The word nummular comes from the same root as numismatic, meaning “coin-shaped” because lesions are round and have the shape of coins.

Prurigo nodularis appears most often on the shins and is seen mainly in adults 20 to 60 years of age. The cause is unknown; however, most patients, but not all, have a personal or family history of atopic dermatitis, asthma, or hay fever. It also may appear in patients with systemic conditions causing persistent itching, such as renal failure. It is seen in the same clinical context as lichen simplex chronicus and may be considered a nodular form of it. Prurigo nodularis tends to be one of the more resistant skin conditions to treat.

Xerosis, or dry skin, is a common occurrence in winter climates, particularly in conditions of cold air, low relative humidity, and indoor heating. In Western societies, where people tend to overbathe and live in overheated spaces, dry skin is a common complaint. The plethora of moisturizing skin care products are testimony to the prevalence of this condition. Xerosis is believed to be caused by diminished production of sebum (asteatosis), as well as by reduced eccrine sweat activity.

Xerosis becomes especially common in the elderly and tends to be most apparent on the hands and lower legs. The word “dry” is sometimes misapplied. Skin that appears to be dry (i.e., showing a buildup of scale) may not always be suffering from a lack of water but from an overadherence or hyperproliferation of scale, which also occurs in patients with ichthyosis (see below).

Asteatotic eczema, also referred to as winter eczema, appears exclusively in adults and most commonly arises on the thighs and shins. This form of eczema is a common, sometimes pruritic, low-grade dermatitis. It is caused by a relative loss of water from the skin through evaporation, a lack of normal desquamation, and, possibly, a decline in the production of sebum.

Ichthyosis vulgaris, the most common form of ichthyosis, first evident in early childhood, is a common disorder that is associated with atopy. Inheritance is autosomal dominant. The term ichthyosis is derived from the Greek root ichthys, meaning fish, because of the resemblance to fish scales.

Typically, shedding of skin occurs unnoticed; however, individuals with ichthyosis produce new skin cells at a rate faster than they can shed them or produce them at a normal rate but shed them too slowly. In either case, there is a buildup of dry, scaly skin. Many patients with hereditary ichthyosis vulgaris have associated atopic manifestations (e.g., asthma, eczema, hay fever). Such atopic conditions can be found in family members, with or without signs of ichthyosis.

Tinea corporis (“ringworm”) is most often acquired by contact with an infected animal or human. It may also be autoinoculated from other areas of the body that are infected by tinea. Majocchi granuloma, a variant of tinea corporis, is defined as a granulomatous folliculitis due to a cutaneous dermatophyte infection. Majocchi granuloma is most commonly due to Trichophyton rubrum infection and less commonly to Trichophyton mentagrophytes and Epidermophyton floccosum. Majocchi granuloma tends to occur in women who frequently shave their legs and it also may appear as a result of the use of potent topical steroids on unsuspected tinea, so-called “tinea incognito.”

Localized plaques of psoriasis on the knees (Fig. 18-9) are similar to those on the elbows where they can be quite hypertrophic (see also Figs. 13-5 and 13-6).

Folliculitis of the legs is seen most often in young adults (see also Mandibular Area and Neck). Causes include actions such as shaving, as well as irritants such as waxing, depilatories, and electrolysis.

Lichen planus (LP) often appears on the shins where it tends to be hypertrophic, less often, atrophic (see Glossary G-9). Its morphology may be characterized by the typical “seven P’s” (see also Arms).

Erythema nodosum (EN) is a type of panniculitis, an acute inflammatory reaction of the subcutaneous fat. It is considered a delayed hypersensitivity reaction to various antigenic stimuli. EN is three times more common in females than in males and has a peak incidence between 20 and 30 years of age.

The most common causes of EN in the United States are sarcoidosis, streptococcal infections, pregnancy, and the use of oral contraceptives. In children, streptococcal pharyngitis is the most likely underlying cause. Approximately 40% of cases are idiopathic. EN also is associated with a variety of other conditions: deep fungal infections in endemic areas, including coccidioidomycosis, histoplasmosis, and blastomycosis; tuberculosis; Yersinia enterocolitica infection; inflammatory bowel disease, including ulcerative colitis and Crohn disease; malignant disease, including lymphoma and leukemia; post-radiation therapy; and Behçet syndrome. In addition, drugs such as sulfonamides, penicillin, gold, amiodarone, and opiates have been implicated as causes of EN.

Nodular vasculitis is an idiopathic panniculitis and vasculitis. When associated with Mycobacterium tuberculosis, it is known as erythema induratum. Erythema induratum is due to the tubercle bacillus and is rare in Western countries. Nodular vasculitis refers to the idiopathic type.