How is atopic dermatitis diagnosed?

Currently, there is no test to diagnose atopic dermatitis and no single symptom or feature used to identify the disease. Each patient experiences a unique combination of symptoms, and the symptoms and severity of the disease may vary over time. The doctor will base his or her diagnosis on the symptoms the patient experiences and may need to see the patient several times to make an accurate diagnosis. It is important for the doctor to rule out other diseases and conditions that might cause skin irritation. In some cases, the family doctor or pediatrician may refer the patient to a dermatologist or allergist (allergy specialist) for further evaluation.

Medical history

Several tools help the doctor better understand a patient's symptoms and their possible causes. The most valuable diagnostic tool is a thorough medical history, which provides important clues. The doctor may ask about:

• Family history of allergic disease
• History of diseases such as hay fever or asthma
• Exposure to irritants
• Sleep disturbances
• Any foods that seem to be related to skin flares
• Previous treatments for skin-related symptoms
• Use of steroids
• The effect of symptoms on schoolwork, career, or social life

Medical tests

Biopsy

Sometimes it is necessary to do a biopsy of the skin or patch testing to see if the skin immune system overreacts to certain chemicals or preservatives in skin creams. A preliminary diagnosis of atopic dermatitis can be made if the patient has three or more features from each of two categories: major features and minor features. Some of these features are listed below.

Skin scratch/prick tests

Skin scratch/prick tests (scratching or pricking the skin with a needle that contains a small amount of a suspected allergen) and blood tests for airborne allergens generally are not as useful in the diagnosis of atopic dermatitis as a medical history and careful observation of symptoms. However, they may occasionally help the doctor rule out or confirm a specific allergen that might be considered important in diagnosis. Although negative results on skin tests are reliable and may help rule out the possibility that certain substances cause skin inflammation in the patient, positive skin scratch/prick test results are difficult to interpret in people with atopic dermatitis and are often inaccurate.

Blood tests

Blood tests, including measurements of certain antibodies to allergens, are not recommended in most cases because they have a high rate of false positives and are expensive. In some cases, where the type of dermatitis is unclear, blood tests to check the level of eosinophils (a type of white blood cell) or IgE (an antibody whose levels are often high in atopic dermatitis) are helpful.

Major and minor features of atopic dermatitis

Major features:

• Intense itching
• Characteristic rash in locations typical of the disease
• Chronic or repeatedly occurring symptoms
• Personal or family history of atopic disorders (eczema, hay fever, asthma)

Some minor features:

• Early age of onset
• Dry, rough skin
• High levels of immunoglobulin E (IgE), an antibody, in the blood
• Ichthyosis
• Hyperlinear palms
• Keratosis pilaris
• Hand or foot dermatitis
• Cheilitis
• Nipple eczema
• Susceptibility to skin infection
• Positive allergy skin tests