eMedicine Specialties > Dermatology > Allergy & Immunology

Atopic Dermatitis: Differential Diagnoses & Workup

Author: Bernice R Krafchik, MBChB, FRCPC, Professor Emeritus, Department of Pediatrics, Section of Dermatology, University of Toronto
Contributor Information and Disclosures

Updated: Jan 19, 2010

Differential Diagnoses

Contact Dermatitis, Allergic
Nummular Dermatitis
Contact Dermatitis, Irritant
Psoriasis, Plaque
Immunodeficiency
Relative zinc deficiency
Lichen Simplex Chronicus
Scabies
Mollusca contagiosa with dermatitis
Seborrheic Dermatitis
Mycosis fungoides
Tinea Corporis

Other Problems to Be Considered

Atopic dermatitis is indistinguishable from other causes of dermatitis. In infancy, the most common difficulty is distinguishing it from SD. This entity is not seen with the same frequency as a decade ago. Both atopic dermatitis and SD are associated with cradle cap (a retention hyperkeratosis) found on the vertex of the scalp, which is greasy and yellow in individuals with SD and dry and crusted in individuals with atopic dermatitis. Other areas of involvement in SD are the intertriginous areas and diaper area; erythema and a greasy scale can be seen over the eyebrows and the sides of the nose. In atopic dermatitis, xerosis of the skin and pruritus occur, which are not usually features of SD. Both conditions should be distinguished from psoriasis.

Scabies manifests in infancy or childhood as a pruritic eruption. Other members of the family are usually itchy, and the primary sites of involvement are moist, warm areas. The eruption is polymorphic with a dermatitis, nodules, urticaria, and 6-10 burrows. Pustules on the hands and feet are almost diagnostic of scabies in infancy. Facial involvement is rare, and xerosis does not occur.

Allergic contact dermatitis from nickel in infants and children is sometimes difficult to distinguish from atopic dermatitis. A central area of dermatitis on the chest from nickel snaps in undershirts or around the umbilicus from snaps in jeans is helpful for making the diagnosis, although a dermatitic eruption may occur as an id reaction in other areas, particularly the antecubital fossae. Xerosis and facial involvement are absent. Atopic dermatitis usually starts earlier than contact dermatitis.

Infants with a severe itch and generalized dermatitis in the setting of recurrent infections should be investigated for evidence of an immunodeficiency. Failure to thrive and repeated infections help distinguish the eruption from atopic dermatitis. In Wiskott-Aldrich syndrome, bleeding may be prominent with the dermatitis, because of the associated thrombocytopenia. In older children, mycosis fungoides (a form of T-cell lymphoma) often presents with hypopigmented patches associated with a dermatitis. This entity is being recognized with increased frequency as physicians become more aware of the disease, and it is sometimes difficult to distinguish between the 2 entities.

Tinea corporis usually manifests as a single lesion, but inappropriate treatment with steroids may cause a widespread dermatitis. Facial involvement, the presence of xerosis, the age of appearance, and an early onset (in atopic dermatitis) help distinguish between the 2 conditions.

One report describes localized varicella lesions developing in preexisting infectious or inflammatory dermatitis; no clear evidence of full-blown chickenpox was seen. The authors suggest viral testing may be needed if vesicular or ulcerative lesions develop within a preexisting dermatitis.13

Workup

Laboratory Studies

  • No chemical marker for the diagnosis of atopic dermatitis is known.
  • Laboratory testing is seldom necessary. A swab of infected skin may help with the isolation of a specific organism and antibiotic sensitivity.
  • Allergy and radioallergosorbent testing is of little value.
  • A platelet count for thrombocytopenia helps exclude Wiskott-Aldrich syndrome, and testing to rule out other immunodeficiencies may be helpful.
  • Scraping to exclude tinea corporis is occasionally helpful.

Histologic Findings

Biopsy shows an acute, subacute, or chronic dermatitis, but no specific findings are demonstrated.

More on Atopic Dermatitis

Overview: Atopic Dermatitis
Differential Diagnoses & Workup: Atopic Dermatitis
Treatment & Medication: Atopic Dermatitis
Follow-up: Atopic Dermatitis
Multimedia: Atopic Dermatitis
References
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References

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Further Reading

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Keywords

atopic dermatitis, eczema, infantile eczema, Besnier's prurigo, intrinsic eczema, extrinsic eczema, atopiform eczema, asthma, food allergy, peanut allergy, allergic reaction

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Contributor Information and Disclosures

Author

Bernice R Krafchik, MBChB, FRCPC, Professor Emeritus, Department of Pediatrics, Section of Dermatology, University of Toronto
Bernice R Krafchik, MBChB, FRCPC is a member of the following medical societies: American Academy of Dermatology, American Dermatological Association, Canadian Medical Association, College of Physicians and Surgeons of Ontario, Royal College of Physicians and Surgeons of Canada, and Society for Pediatric Dermatology
Disclosure: Nothing to disclose.

Medical Editor

Peter Fritsch, MD, Chair, Department of Dermatology and Venereology, University of Innsbruck, Austria
Peter Fritsch, MD is a member of the following medical societies: American Dermatological Association, International Society of Pediatric Dermatology, and Society for Investigative Dermatology
Disclosure: Nothing to disclose.

Pharmacy Editor

Richard P Vinson, MD, Assistant Clinical Professor, Department of Dermatology, Texas Tech University School of Medicine; Consulting Staff, Mountain View Dermatology, PA
Richard P Vinson, MD is a member of the following medical societies: American Academy of Dermatology, Association of Military Dermatologists, Texas Dermatological Society, and Texas Medical Association
Disclosure: Nothing to disclose.

Managing Editor

Van Perry, MD, Assistant Professor, Department of Medicine, Division of Dermatology, University of Texas Health Science Center
Van Perry, MD is a member of the following medical societies: American Academy of Dermatology and American Society for Laser Medicine and Surgery
Disclosure: Nothing to disclose.

CME Editor

Catherine M Quirk, MD, Clinical Assistant Professor, Department of Dermatology, University of Pennsylvania
Catherine M Quirk, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Dermatology
Disclosure: Nothing to disclose.

Chief Editor

Dirk M Elston, MD, Director, Department of Dermatology, Geisinger Medical Center
Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology
Disclosure: Nothing to disclose.

 
 
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