Many skin conditions that affect the arms result from exposure to sunlight, contact allergens or irritants, trauma, bug bites, and other environmental insults. The arms are within close reach of the contralateral hand so patients can easily scratch pruritic dermatoses. Scratching or trauma may produce a linear streak of papules (Koebner reaction) in certain diseases such as lichen planus and psoriasis. Some skin diseases have a predilection for specific locations on the arms. While it is unknown why many dermatoses have a tendency to localize to certain anatomical locations, lesion distribution is frequently a very important clue to establish diagnosis.
Skin diseases primarily involving the arms can be broadly categorized according to their etiology. These include inflammatory, infectious, neoplastic, and photodermatoses (see Table 32-1). The distribution of skin lesions is often helpful in diagnosing skin diseases located on the arms. For example, psoriasis usually favors the extensor surface (especially the elbows), photodermatoses affect areas exposed to light, keratosis pilaris is typically seen on the proximal dorsal arms, and atopic dermatitis generally affects the extensor surface in infants and flexural surface in children and adults. Lichen planus is commonly located on the volar wrist and flexural surfaces and nummular dermatitis on extensor surfaces.
| Disease | Epidemiology | History | Physical Examination |
|---|---|---|---|
| Inflammatory | |||
| Atopic dermatitis | Common M ≥ F Age: usually presents in childhood, but may persist | Pruritic. Chronic course with exacerbations Usually worse in winter Family or personal history of atopy | Infants: red papules, scaly plaques, and excoriations on extensor arms Children and adults: red lichenified plaques, prurigo nodules, and excoriations on flexor arms, especially antecubital fossae (Figure 8-8) |
| Keratosis pilaris | Very common. Often seen with atopic dermatitis | Usually asymptomatic. Rarely, mildly pruritic | Follicular-based keratotic papules with peripheral erythema. Stippled or “goosebumps” appearance on extensor surfaces (Figure 8-9) |
| Allergic contact dermatitis | Common F > M Age: any age | Pruritic and painful fissures. Onset is hours to days after contact with allergen | Acute: papules and vesicles on an erythematous base (Figures 8-4 and 8-5) Chronic: xerosis, fissuring, hyperpigmentation, and lichenification at sites of direct contact with allergen (Figure 8-6) |
| Psoriasis vulgaris | Common. M = F Onset at any age but peaks in 20s and 50s | Asymptomatic or mildly pruritic. Chronic Associated with arthritis Family history of psoriasis | Red papules and plaques with silvery, thick, adherent scale on elbows and extensor surface (Figure 9-1) |
| Lichen planus | Uncommon F > M Age: 30-60 years | Pruritic or symptomatic Lasts months to years May be drug-induced or associated with hepatitis C | Classically flat-topped, well-defined, polygonal, violaceous, shiny papules on volar wrist and flexor arms (Figures 9-10 and 9-11) |
| Lichen simplex chronicus | Common F > M Age >20 years. More common in atopic patients | Paroxysmal episodes of pruritus disproportionate to external stimuli (eg, changing clothes). Emotional stress may exacerbate | Sharply defined round, oval, or linear plaque(s) comprised of confluent dull pink-red papules with excoriations on extensor arms (Figure 8-13) |
| Nummular eczema | Common M > F Age: bimodal; peaks in young adults and the elderly | Pruritic Chronic waxing and waning course Associated with dry skin | Round, light pink, scaly, thin, 1-3 cm plaques on extensor arms (Figure 8-11) |
| Infectious | |||
| Tinea corporis | Common M:F unknown Age: all. More common in hot humid areas, farms, and crowded living conditions | Mild pruritus History of contact with infected people or animals. Outbreaks seen in daycare facilities, schools, and wrestlers | Solitary or grouped well-demarcated red annular plaques with raised border with peripheral scale (Figure 10-4) |
| Photodermatoses. See Chapter 31 (Skin Diseases of the Face) | |||
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