Atopic dermatitis

Overview

• A chronic, pruritic, relapsing inflammatory skin disease classically described as "the itch that rashes," with the flexural surfaces as its home territory.
• Pathogenesis is multifactorial, related to a compromised skin barrier and an underlying immune response, with S. aureus secondary infection favored by a decrease in antimicrobial peptides in affected skin.
• Part of the atopic triad: dermatitis, asthma, and allergic rhinitis frequently coexist in the same patient.
• Presentation differs by stage: acute lesions weep and crust, chronic lesions become scaled, lichenified, and hyperpigmented from repeated scratching.
• Treatment is directed at barrier repair and controlling inflammation, stepping up from topical measures to systemic therapy in recalcitrant disease.

Epidemiology

• A common condition seen across primary care and dermatology, with flares recurring over a patient's lifetime rather than a single self-limited episode.
• Frequently associated with the other atopic diseases, allergic rhinitis and asthma, which should be sought on history in any patient with atopic dermatitis.
• Can persist into or recur in adulthood, with continued mild flares requiring intermittent treatment in some patients despite childhood-predominant onset.

Risk factors

• A personal or family history of atopy (asthma, allergic rhinitis, atopic dermatitis), reflecting the shared genetic and immune predisposition of the atopic triad.
• Compromised skin barrier function, which allows increased transepidermal water loss and antigen penetration that drive the inflammatory response.
• Use of fragranced or soap-based cleansers and moisturizers, which can provoke irritation and flares in barrier-impaired skin, the rationale for fragrance-free, non-soap-based skin care.
• Reduced antimicrobial peptide activity in affected skin, which predisposes to secondary S. aureus infection and flare.

Pathophysiology

• A compromised epidermal skin barrier allows increased water loss and easier penetration of irritants and allergens into the skin.
• An underlying immune response amplifies inflammation once the barrier is breached, producing the pruritic, eczematous eruption.
• Decreased antimicrobial peptides in affected skin create a favorable environment for S. aureus colonization and secondary infection, which is why acute worsening with pustules and honey-colored crusting signals bacterial superinfection rather than a simple flare.
• Chronic scratching in response to pruritus drives lichenification, the thickened, hyperpigmented skin change that marks longstanding disease.

Clinical features

• Intense pruritus is the defining symptom, driving the scratch-itch cycle that shapes the clinical picture from an acute weeping flare into chronic lichenified disease.
• Face and flexural surfaces (popliteal and antecubital fossae) are the classic distribution.
• Acute atopic dermatitis: pruritic, erythematous patches or plaques with weeping and crusting.
• Chronic atopic dermatitis: scaling with lichenification and hyperpigmentation of the skin from repeated scratching.
• Bacterial superinfection (S. aureus): acute worsening of established dermatitis with pustules and honey-colored crusting, a distinct pattern from an uncomplicated flare.
• Associated atopic triad features, allergic rhinitis and asthma, are frequently present in the same patient and support the diagnosis when the skin findings are equivocal.

Differential diagnosis

• Allergic contact dermatitis: sharply marginated, geometric or linear patches confined to the site of contact with an allergen (for example a new facial product), unlike the ill-defined, symmetric flexural distribution of atopic dermatitis.
• Irritant contact dermatitis: favors the hands and sites of repeated wet work, non-immune mediated, rather than the flexural, atopy-associated pattern of atopic dermatitis.
• Seborrheic dermatitis: greasy, yellowish scale on the scalp, nasolabial folds, and eyebrows, without the flexural popliteal and antecubital involvement typical of atopic dermatitis.
• Psoriasis: well-demarcated, erythematous plaques with silvery scale, typically on extensor surfaces and scalp, unlike the ill-defined, flexural, intensely pruritic lesions of atopic dermatitis.
• Scabies: intensely pruritic papules with burrows, favoring finger webs, wrists, and genitals, with a history of similarly affected close contacts, unlike the classic flexural atopic dermatitis distribution.
• Tinea corporis: an annular plaque with central clearing and an active scaling border, confirmed by a positive potassium hydroxide preparation, unlike the ill-defined, non-annular plaques of atopic dermatitis.
• Dyshidrotic eczema: intensely pruritic, deep-seated vesicles on the palms, soles, and lateral fingers rather than the popliteal and antecubital flexures of classic atopic dermatitis.
• Nummular eczema: coin-shaped, well-demarcated plaques rather than the ill-defined flexural patches of atopic dermatitis, though both can coexist in the same patient.
• Psoriasis or atopic dermatitis flaring to erythroderma: diffuse erythema and scale following injudicious use and abrupt cessation of systemic glucocorticoids, distinguished from a routine flare by its diffuse, whole-body extent and the preceding steroid taper.

Diagnosis

• This is a clinical diagnosis established by the combination of intense pruritus, the characteristic face and flexural distribution, and a personal or family history of the atopic triad (dermatitis, asthma, allergic rhinitis).
• First, stage the presentation as acute or chronic: weeping, crusting, erythematous patches point to an acute flare, while scaling, lichenification, and hyperpigmentation point to chronic disease.
• Then, examine for signs of bacterial superinfection: pustules with honey-colored crusting on a background of established dermatitis indicate S. aureus superinfection and change management, warranting a low threshold to treat.
• If the distribution is atypical (sharply geometric, confined to a contact site, or annular with an active border), reconsider the diagnosis and evaluate for allergic contact dermatitis or tinea corporis before treating as atopic dermatitis.

Clinical pearl. Honey-colored crust superimposed on established eczema is impetiginization from S. aureus, not just a bad flare, have a low threshold to treat the infection, since topical steroids alone will still help the surrounding eczema but will not clear the bacterial component.

Management

• First, use fragrance-free, non-soap-based cleansers and bland emollients, applied consistently as the foundation of therapy for all severities.
• For an active flare, apply a topical glucocorticoid, for example triamcinolone acetonide 0.1% cream or ointment, a thin layer to active lesions twice daily until clear, avoiding prolonged use on the face, folds, and genital skin.
• If disease affects the face or skin folds where prolonged or potent topical glucocorticoid use risks atrophy, switch to a topical calcineurin inhibitor: tacrolimus ointment 0.1% (0.03% for children age 2 to 15 years), a thin layer twice daily, stopping when signs and symptoms resolve and re-examining if not improved by 6 weeks; pimecrolimus cream 1% is an alternative, applied twice daily and re-examined if symptoms persist beyond 6 weeks.
• Proactive maintenance therapy with a topical glucocorticoid once to twice weekly in areas that commonly flare can be used to prevent relapse once the acute flare has cleared.
• If bacterial superinfection is present (pustules, honey-colored crusting), treat the S. aureus infection while continuing topical glucocorticoids for the surrounding eczema.
• Avoid systemic glucocorticoids when possible, since flares commonly follow discontinuation; reserve them for severe exacerbations or as a bridge to another systemic therapy.
• If disease remains moderate to severe and is recalcitrant to topical agents, escalate to systemic therapy:
  • Dupilumab, an initial 600 mg subcutaneous dose given as two 300 mg injections, then 300 mg subcutaneously every 2 weeks, effective at decreasing pruritus and disease activity.
  • Phototherapy as a nonpharmacologic escalation option.
  • Steroid-sparing systemic agents, cyclosporine, methotrexate, azathioprine, or mycophenolate mofetil, as additional options for recalcitrant disease.

Complications

• Bacterial superinfection with S. aureus, presenting as acute worsening with pustules and honey-colored crusting, the most common infectious complication.
• Lichenification and hyperpigmentation from chronic scratching, a marker of longstanding, inadequately controlled disease.
• Erythroderma, which can follow injudicious use and abrupt cessation of systemic glucocorticoids in a patient with atopic dermatitis.
• Permanent skin atrophy, striae, or telangiectasia from prolonged or potent topical glucocorticoid use, particularly on thin facial or flexural skin, which is why topical calcineurin inhibitors are preferred for these sites in extended use.
• Rare skin cancer or cutaneous lymphoma risk with topical calcineurin inhibitors, reflected in a black-box warning for tacrolimus and pimecrolimus despite their steroid-sparing benefit.

Prognosis

• Most disease is well controlled with emollients and topical anti-inflammatory therapy, with acute flares clearing over the twice-daily glucocorticoid course.
• Disease tends to relapse without maintenance care, which is why proactive once- to twice-weekly topical glucocorticoid application to flare-prone areas reduces recurrence.
• Recalcitrant, moderate to severe disease responds to dupilumab, with decreased pruritus and disease activity in patients who have failed topical agents.
• Systemic glucocorticoid use is followed by a high risk of flare on discontinuation, reinforcing that these agents are a bridge rather than a durable solution.

Prevention

• Routine use of fragrance-free, non-soap-based cleansers and bland emollients, applied immediately after bathing, as the ongoing barrier-protective measure that reduces flare frequency.
• Proactive maintenance topical glucocorticoid application once to twice weekly in historically flare-prone areas to prevent relapse after a flare has cleared.
• Avoiding abrupt discontinuation of systemic glucocorticoids, using a taper instead, to prevent rebound flare or erythroderma.
• Prompt treatment of bacterial superinfection when honey-colored crusting appears, to prevent escalation of an infected flare.

Key points

• Atopic dermatitis is a chronic, relapsing, intensely pruritic eczema of the face and flexural surfaces, part of the atopic triad with asthma and allergic rhinitis.
• Acute disease weeps and crusts; chronic disease lichenifies and hyperpigments from repeated scratching.
• Honey-colored crusting on established eczema signals S. aureus superinfection, not just a worse flare, and warrants a low threshold to treat.
• First-line therapy is barrier care (fragrance-free cleansers, emollients) plus a topical glucocorticoid for active flares, applied twice daily until clear.
• Topical calcineurin inhibitors (tacrolimus, pimecrolimus) are steroid-sparing options for the face and folds, avoiding the atrophy risk of prolonged topical steroids.
• Dupilumab is reserved for moderate to severe disease recalcitrant to topical therapy, dosed as a 600 mg subcutaneous load then 300 mg every 2 weeks.