Nummular dermatitis is a persistent, usually itchy rash and inflammation of the skin characterized by coin-shaped spots and scale.
(See also Overview of Dermatitis.)
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.
MION/PHANIE/SCIENCE PHOTO LIBRARY
Image courtesy of Karen McKoy, MD.
Image courtesy of Karen McKoy, MD.
MION/PHANIE/SCIENCE PHOTO LIBRARY
Image courtesy of Karen McKoy, MD.
Image courtesy of Karen McKoy, MD.
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).
If people do not have atopy (a combination of atopic dermatitis, hay fever, and asthma), they sometimes undergo patch testing. In patch testing, 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
Skin care
Anti-itch medications and corticosteroid creams
Sometimes phototherapy
Treatment of nummular dermatitis is similar to that of atopic dermatitis and includes counseling about general skin care, anti-itch medications, corticosteroids, and sometimes phototherapy.
Rarely, immunosuppressive medications taken by mouth are needed.
