(See also Overview of Dermatitis Overview of Dermatitis Dermatitis is inflammation of the upper layers of the skin, causing itching, blisters, redness, swelling, and often oozing, scabbing, and scaling. Known causes include dry skin, contact with... read more .)
The cause of nummular dermatitis is unclear. It often develops in people who have hay fever or asthma. Sometimes certain bacteria that inhabit the skin (called bacterial colonization) appear to cause nummular dermatitis. An allergic reaction to a substance a person has come in contact with is also a possible cause. Sometimes spots appear on an area of the body that is not the area where the infection or reaction first began.
Nummular dermatitis usually affects middle-aged and older people.
Symptoms of Nummular Dermatitis
The round spots start as red, itchy, and scaly spots that are shaped like coins. The spots may be widespread. Often, spots are more obvious on the backs of the arms or legs and on the buttocks, but they also appear on the torso.
Diagnosis of Nummular Dermatitis
A doctor's examination of the skin
Sometimes a skin biopsy
Sometimes a patch test to determine a contact allergy
Doctors base the diagnosis of nummular dermatitis on the characteristic appearance of the spots. They sometimes take samples of skin and send them to a laboratory ( biopsy Biopsy Doctors can identify many skin disorders simply by looking at the skin. A full skin examination includes examination of the scalp, nails, and mucous membranes. Sometimes the doctor uses a hand-held... read more ).
If people do not have atopy (a combination of atopic dermatitis Atopic Dermatitis (Eczema) Atopic dermatitis (commonly referred to as eczema) is chronic, itchy inflammation of the upper layers of the skin that often develops in people who have hay fever or asthma and in people who... read more , hay fever Seasonal Allergies Seasonal allergies result from exposure to airborne substances (such as pollens) that appear only during certain times of the year. Seasonal allergies cause itchy skin, a runny nose, sneezing... read more , and asthma Asthma Asthma is a condition in which the airways narrow—usually reversibly—in response to certain stimuli. Coughing, wheezing, and shortness of breath that occur in response to specific triggers are... read more ), they sometimes undergo patch testing. In patch testing Skin tests Doctors can identify many skin disorders simply by looking at the skin. A full skin examination includes examination of the scalp, nails, and mucous membranes. Sometimes the doctor uses a hand-held... read more , small patches containing standard contact allergens are placed on the skin of the upper back and left on for 48 hours to see whether a rash develops beneath one of them. After 48 hours, they are removed, and the doctor evaluates the skin underneath. The skin is evaluated again a day or two later.
Treatment of Nummular Dermatitis
Anti-itch drugs and corticosteroid creams
Treatment of nummular dermatitis is similar to that of atopic dermatitis Treatment Atopic dermatitis (commonly referred to as eczema) is chronic, itchy inflammation of the upper layers of the skin that often develops in people who have hay fever or asthma and in people who... read more and includes counseling about general skin care, anti-itch drugs, corticosteroids, and sometimes phototherapy.
Dupilumab injections, creams that contain tacrolimus or pimecrolimus, crisaborole ointment, or a combination may be given to some people.
Rarely, immunosuppressive drugs taken by mouth are needed.