What are the differences between atopic dermatitis rash and scabies rash?

Distinguishing Atopic Dermatitis from Scabies

Atopic dermatitis presents with symmetrical, age-specific eczematous lesions and chronic relapsing pruritus, while scabies shows asymmetric distribution with characteristic burrows in interdigital spaces, axillary, inguinal, and genital areas. 1, 2

Key Distinguishing Features

Distribution Pattern

• Atopic dermatitis displays symmetrical distribution that varies by age: in infants, lesions commonly affect cheeks, scalp, and extensor surfaces of extremities 3, 1
• Scabies presents asymmetrically with predilection for interdigital web spaces, wrists, axillae, genitalia, and inguinal regions 2
• The symmetrical pattern is a core diagnostic criterion for atopic dermatitis, making asymmetric presentations highly suspicious for alternative diagnoses 2, 1

Morphology of Lesions

• Atopic dermatitis manifests as erythematous, eczematous patches with xerosis, erosions/excoriations, oozing, crusting, and lichenification depending on chronicity 1
• Scabies characteristically shows burrows (pathognomonic linear or serpiginous tracks), papules, and vesicles, particularly in finger web spaces 2
• Atopic dermatitis lesions are primarily inflammatory with dry, desquamating skin, while scabies burrows represent the mite's tunneling activity 1

Clinical Course and Timing

• Atopic dermatitis follows a chronic, relapsing course with approximately 80% developing symptoms within the first 5 years of life 1, 3
• Scabies has acute to subacute onset with rapid progression of intensely pruritic lesions over days to weeks 2
• Atopic dermatitis symptoms persist for months to years with exacerbations and remissions, whereas scabies continues to worsen without treatment 1

Pruritus Characteristics

• Atopic dermatitis causes chronic, persistent pruritus that worsens with triggers like sweating, temperature changes, and irritants 1, 3
• Scabies produces intense nocturnal pruritus that is classically worse at night when the mites are most active 2

Associated Features

• Atopic dermatitis commonly presents with personal or family history of atopy (asthma, allergic rhinitis), elevated IgE, and peripheral eosinophilia 1, 3
• Scabies often affects multiple household members or close contacts simultaneously, providing epidemiologic clues 2

Critical Diagnostic Pitfalls

Overlapping Presentations

• Scabies can coexist with or mimic atopic dermatitis, particularly in infants where both conditions cause widespread erythema and pruritus 4
• Failure to respond to appropriate atopic dermatitis therapy should prompt reconsideration of the diagnosis and evaluation for scabies or other conditions 2
• Iatrogenic immunosuppression from corticosteroid treatment of presumed atopic dermatitis can lead to crusted (Norwegian) scabies in misdiagnosed cases 4

Confirmatory Testing

• Skin scraping for microscopic examination is essential when scabies is suspected, looking for mites, eggs, or fecal pellets 2
• Atopic dermatitis diagnosis remains clinical without specific laboratory confirmation, based on characteristic features and distribution 1, 3

Age-Specific Considerations

• In neonates and young infants, the physiological inability to mount a scratching reaction combined with atopic predisposition can lead to atypical scabies presentations that are easily confused with atopic dermatitis 4
• Infants with scabies may show involvement of palms, soles, face, and scalp—areas less commonly affected in older children with scabies 4

When to Suspect Scabies Over Atopic Dermatitis

• Asymmetric or localized distribution rather than the expected symmetrical pattern 2, 1
• Presence of burrows on careful examination, particularly between fingers and toes 2
• Involvement of multiple family members with similar symptoms 2
• Predominant nocturnal pruritus out of proportion to visible skin changes 2
• Lack of response to appropriate topical corticosteroids and emollients after 2-4 weeks 2, 3