Often appearing after a skin injury,
such as a burn, abrasion, or insect bite, the hallmark of this
common eczema is unique, coin-shaped (nummular) or oval lesions. One
or many patches can develop that may last for weeks or months.
dermatitis causes distinct coin-shaped or oval lesions that
often itch and burn.
nummular dermatitis more frequently than women and tend to
have their first outbreak between 55 and 65 years of age.
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National Library of Dermatologic Teaching Slides)
Signs and Symptoms
One or several patches may appear and
Begin as a group of tiny reddish
spots and blister-like lesions that enlarge and grow together to
form a reddened, coin-shaped patch that ranges in size from less
than 1 inch to more than 4 inches.
Weep fluid in the beginning and
then become crusty. Long-term patches are scaly.
Be pink, red, or brown and
Develop on the legs, but also occur
on the torso, arms, hands, and feet.
Clear in the center, forming a
“ring” around the clear skin that causes the patch to resemble a
Patches often itch and burn. Itching
and burning range from severe to barely noticeable. The itch may
intensify at night, disturbing sleep.
A yellowish crust may develop on the
patches if a Staphylococcus aureus (staph) infection
While the skin between the patches
usually remains clear, the skin may be very dry and easily
When this type of eczema clears, it
often leaves the skin a bit darker (hyperpigmentation) or lighter
(hypopigmentation) than the surrounding skin. The discoloration
may never fade completely when a lesion occurs below the knee.
In the United States, approximately 2
out of every 1,000 people develop nummular eczema.
Men develop it more frequently and
tend to have their first outbreak between 55 and 65 years of age.
Another peak period for developing nummular dermatitis is between
the ages of 15 and 25 years. Women are more likely to develop the
Rare in children.
While the cause remains unknown, researchers believe that
heightened sensitivity plays a role in most cases. Some patients
show sensitivity to:
Mercury. It is believed that
in rare cases, exposure to mercury, which is a common component of
dental fillings, can cause nummular dermatitis. Research shows
that a few patients with nummular dermatitis only cleared, despite
numerous treatments, when all of their mercury-containing fillings
were removed. Even handling the materials in a dental office or
lab has been shown to cause an outbreak, which leads researchers
to believe that inhaling the mercury vapor may be the cause in
Rubber, nickel, formaldehyde, or
neomycin. If the patient has an allergy to any of these, the
skin will only clear when the substance is avoided.
The following seem to increase the risk of developing nummular
Medical condition. A history
of very dry skin (xerosis) or eczema, especially atopic dermatitis
or stasis dermatitis, increases the risk as does having poor blood
flow and/or swelling in the legs.
Environment. A low-humidity
environment, especially one that also is cold seems to increase
the risk as well as worsen existing nummular dermatitis.
Injury to the skin. An insect
bite, contact with chemicals, or an abrasion may trigger an
Bacterial skin infection.
Isotretinoin, a prescription medication used to treat severe acne
that proves resistant to other treatments, seems to increase the
risk. Some patients who are treated for hepatitis C with
interferon develop severe, generalized (widespread lesions on the
body) nummular dermatitis.
Visual examination. Diagnosis
usually begins with a visual exam of the patient’s skin. During
the exam, the dermatologist may take samples if a skin infection
Patch testing. If an allergy
is suspected, patch testing (medical testing to find allergies) is
advised. Patch testing also is advised when treatment does not
effectively clear the condition.
With proper treatment, nummular dermatitis can clear completely.
However, lesions on the lower extremities often take longer to heal
and tend to leave spots. The treatment plan for nummular eczema
Protecting the skin from further
Hydrating the skin. Taking a
short, lukewarm bath or shower once a day and immediately applying
a cream or ointment to still-damp skin can help hydrate dry skin
as well as relieve the itch and scaling. Adding a bath oil to the
water also may help.
Using medication as directed.
Topical corticosteroids and tar preparations help reduce
inflammation and itch. If a bacterial skin infection develops, it
is treated with an antibiotic. An antihistamine can help a patient
When a patient develops severe or generalized (widespread lesions)
nummular dermatitis, treatment may require special dressings,
phototherapy (treatment with ultraviolet light), oral antibiotics,
systemic (taken by mouth or injected) corticosteroids, and bed
rest in a cool, moist environment.
To prevent nummular dermatitis from
recurring once the skin clears, dermatologists recommend:
Moisturizing. Applying a
moisturizer at least daily, and after bathing helps, especially in
a dry climate. Moisturizer helps trap water in the skin. A
dermatologist can recommend suitable products that will not
irritate the skin.
Avoiding certain activities.
Anything that dries, heats, or irritates the skin, such as hot
baths, frequent bathing, or sitting next to a fire, can cause a
Modifying skin care. Using
only a mild, non-drying cleanser (not soap) when bathing helps.
Using a humidifier. When
heating or air-conditioning is necessary, use a humidifier to add
moisture to the air.
Dressing for success. Wear
loose clothing, and avoid wearing rough fabrics, such as wool,
which can irritate the skin.
Adachi A et al. “Mercury-induced nummular dermatitis.”
Journal of the American Academy of Dermatology, 2000
August;43(2, part 2) 383-385.
Jarvikallio A et al. “Quantitative analysis of tryptase- and chymase-containing
mast cells in atopic dermatitis and nummular eczema.” British
Journal of Dermatology, 1997 June;136(6):871-877.
Sotor NA. “Nummular eczematous eczema.” In: Freedberg IM et al
(eds.) Fitzpatrick’s Dermatology in General Medicine, 5th ed.
New York: McGraw Hill; 1999:1480-1482.
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cause of nummular dermatitis remains a mystery, researchers do know
that the condition does not run in families and is not caused by a