Differentials
Seborrheic dermatitis
SIGNS / SYMPTOMS
Characteristic greasy scale that is not pruritic. Often affects cheeks, scalp, extremities, and trunk. Unlike atopic dermatitis, the diaper area is often affected.
INVESTIGATIONS
Clinical exam is the best tool to differentiate between these lesions.
Irritant contact dermatitis
SIGNS / SYMPTOMS
Common in diaper area, face, and extensor surfaces in children; results from exposure to irritating substances. Typically less pruritic than atopic dermatitis.
INVESTIGATIONS
Elimination of irritants will result in clinical improvement.
Patch testing may be positive for relevant irritants.
May be limited role for skin biopsy (e.g., patch tests are negative, chronic disease, uncertain diagnosis), which can identify whether contact dermatitis is present. Skin biopsy does not distinguish irritant contact dermatitis from allergic contact dermatitis.
Allergic contact dermatitis
SIGNS / SYMPTOMS
Well-circumscribed erythematous lesions, often with spongiotic papules, vesicles, and crusting. Lesions are usually pruritic and asymmetric (unlike those associated with atopic dermatitis, which are typically symmetric). Eruptions are due to contact with specific allergen, and removal of offending agent results in resolution of symptoms.
INVESTIGATIONS
Elimination of allergic stimuli results in resolution of dermatitis.
Patch testing may be positive for relevant allergen.
May be limited role for skin biopsy (e.g., patch tests are negative, chronic disease, uncertain diagnosis), which can identify whether contact dermatitis is present. Skin biopsy does not distinguish irritant contact dermatitis from allergic contact dermatitis.
Scabies
SIGNS / SYMPTOMS
Severe pruritus, particularly at night. In addition to papules or vesicles, burrows may be evident and will help to make the diagnosis. The wrists, ankles, palms, soles, interdigital spaces, axillae, waist, and groin are the most commonly affected sites. Patients will often report similar symptoms in family members or other close contacts.[66]
INVESTIGATIONS
Microscopy may reveal mites, eggs, or scybala (mite feces).
Psoriasis
SIGNS / SYMPTOMS
Well-circumscribed, erythematous lesions with silver scale that show a predilection for extensor surfaces, particularly elbows and knees.
The nail pitting seen in psoriasis has smaller pits and is more common than that seen in patients with atopic dermatitis.
INVESTIGATIONS
This is usually a clinical diagnosis. No laboratory testing is typically necessary to distinguish between atopic dermatitis and psoriasis.
If the diagnosis is uncertain, there may be a limited role for skin biopsy, which may not always reveal the classic features of psoriasis.
Mycosis fungoides
SIGNS / SYMPTOMS
The initial stages of mycosis fungoides (cutaneous T-cell lymphoma) may look similar to atopic dermatitis. Erythematous plaques in random distribution are common and scale is often present. As opposed to patients with atopic dermatitis, patients with mycosis fungoides tend to be older at the time of diagnosis, with an average age ≥50 years.[67]
INVESTIGATIONS
Skin biopsy is necessary to make the diagnosis of mycosis fungoides.
Additional studies that encompass cell flow cytometry may be used to confirm the diagnosis.
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