Skin Diseases of the Legs

INTRODUCTION TO CHAPTER

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The legs are predisposed to dermatoses that are gravity dependent, including stasis dermatitis and vascular conditions such as leukocytoclastic vasculitis, the pigmented purpuric dermatoses, and livedo reticularis. Legs are also the site of frequent trauma and thus are susceptible to conditions that may be induced by trauma including superficial thrombophlebitis, pyoderma gangrenosum, necrobiosis lipoidica, chronic ulcers, and cellulitis. In patients with preexisting vascular conditions affecting the lower extremities, including diabetes mellitus, venous insufficiency, and peripheral vascular disease, traumatic wounds may take longer to heal and may have an increased risk of infection.

APPROACH TO DIAGNOSIS

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Skin diseases primarily involving the legs can be broadly categorized into inflammatory conditions, infectious diseases, superficial vascular disorders, neoplastic lesions, and underlying systemic diseases (see Table 35-1). Differentiating between these conditions can usually be done based on an appropriate history and physical examination. Occasionally, dermatitis on the lower extremities may be difficult to distinguish from a cellulitis. Cellulitis of the lower extremities tends be unilaterally, as compared to dermatitis, which usually is bilateral.

Table 35-1.Differential diagnosis for diseases of the legs.

Disease	Epidemiology	History	Physical Examination
Inflammatory
Asteatotic dermatitis	Common M > F Age: typically >60 years	Pruritus and dry skin Waxing and waning course Worse in winter	Dry, fissured, cracking, mildly scaly and inflamed plaques on bilateral anterior lower legs (Figure 8-3)
Stasis dermatitis	Common F > M Age: middle-aged and elderly adults	Asymptomatic or pruritic Associated with leg swelling	Erythematous, scaly plaques, may be hyperpigmented, lichenified, or sclerotic on bilateral anterior lower legs, especially medial ankles (Figure 29-1)
Nummular eczema	Common M > F Age: Adults	Pruritus Chronic, waxing, and waning course Worse in fall and winter	Round, light pink, scaly, thin, 1-3 cm plaques on legs (Figure 8-11)
Psoriasis vulgaris	Common M = F. Onset at any age but peaks in 20s and 50s	Asymptomatic to mildly pruritic. Chronic course. May be associated with arthritis Family history of psoriasis	Red papules and plaques with silvery, thick, adherent scale, commonly on knees (Figure 9-1)
Erythema nodosum	Uncommon F > M Age: 20-40 years	Tender lesions Variable course May be associated with fevers and arthralgias	Indurated, tender, red, deep, poorly defined nodules, usually on bilateral shins (Figure 24-14)
Pyoderma gangrenosum	Rare F ≥ M Age: all ages, but typically 30-40 years	Painful. May last months to years Spontaneous healing may occur	Initially, a hemorrhagic pustule with surrounding erythema. Later, ulceration with granulation tissue, eschar and purulent material at the base, and a dusky red/purple border (Figure 2-13)
Infectious
Cellulitis	Common M = F Age: more common in older adults	Pain, swelling, fever, chills, and malaise Increased risk in diabetics	Localized warm, red, tender plaque with ill-defined borders, usually on lower leg (Figure 12-3)
Tinea corporis	Common M > F Age: any age	Mild pruritus History of concomitant tinea pedis	Solitary or grouped, well-demarcated red annular plaques with a raised border and peripheral scale (Figure 10-4). Sometimes peripheral vesicles or pustules
Neoplastic
Stucco keratoses	Common M > F Age: older adults	Asymptomatic and usually unnoticed	Keratotic, stuck on appearing, whitish-grey papules bilaterally on extensor surface (Figure 16-3)
Systemic
Diabetic dermopathy	Uncommon M:F unknown Age: usually >50 years	Asymptomatic Appears in crops. Slowly resolves with scarring	Well-circumscribed, round, atrophic, and hyperpigmented plaques that heal with scarring on bilateral shins
Necrobiosis lipoidica	Uncommon F > M Age: young adults	Usually asymptomatic, but may ulcerate and become painful. Gradual onset, may last years. One-third have history of diabetes or minor trauma	Well-demarcated, shiny plaque with a mildly elevated erythematous border and an atrophic, yellowish, waxy center on bilateral shins (Figure 24-8)
Thrombocytopenic purpura (TTP)	Uncommon M = F Age: any age, depending on etiology	Asymptomatic Onset: hours Associated with low platelets due to HIV, TTP, ITP, DIC, drugs, infections, and bone marrow dyscrasias	Petechiae: pinpoint, nonblanching, nonpalpable red macules (Figure 25-1) Ecchymosis: larger red macules and black-and-blue patches
Vascular
Superficial thrombophlebitis	Uncommon M:F unknown Age: young to middle aged adults	Asymptomatic or tender Idiopathic or due to trauma, infection, IV extravasation, or migratory thrombophlebitis	Red and tender subcutaneous cord with swelling along the course of a vein Can occur on the trunk or extremities, but most commonly occurs on the legs
Leukocytoclastic vasculitis.	Uncommon M = F Age: all ages	Asymptomatic, pruritic, or tender. Duration: days to years depending on etiology. Idiopathic or due to drugs, underlying CVD, infections, or malignancy	Classic presentation is palpable purpura/petechiae with bright red well-defined macules and scattered red papules on lower legs and ankles (Figure 25-4)
Pigmented purpuric dermatosis (Schamberg’s disease)	Common M > F Age: typically 30-60 years	Asymptomatic or mildly pruritic. Slowly evolving over months. Chronic course, lasting years	Characteristic purpuric, speckled, “cayenne pepper-like” macules or less commonly annular plaques and lichenoid papules on lower legs
Physiologic livedo (cutis marmorata)	Common M:F unknown Age: more apparent in neonates, infants, and children	Asymptomatic A physiologic phenomenon that occurs in the cold	Purple discoloration of the skin in a netlike distribution on the lower extremities that resolves with warming
Primary and secondary pathologic livedo reticularis (LR)	Uncommon M < F Age: 20-30 years of age	Asymptomatic. Secondary LR is associated with conditions that cause vasospasm, increased blood viscosity, vasculitis, or intravascular obstruction	Purple discoloration of the skin in a netlike distribution on the lower extremities that persists after rewarming (Figure 2-28)