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Chapter 32: Skin Diseases of the Arms

Steven W. Lin; Noah Goldfarb

INTRODUCTION TO CHAPTER

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.

APPROACH TO 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.

Table 32-1.Differential diagnosis for diseases of the arms.
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Table 32-1. Differential diagnosis for diseases of the arms.
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

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