What Is Nummular Eczema?

Nummular eczema, also called discoid eczema or discoid dermatitis, is a type of localised dermatitis (inflammation of the skin). Nummular eczema is characterised by a circular or oval shaped patch, or patches, of inflamed, dry and scaly skin, which can be swollen, blistered, and oozing pus. Discoid dermatitis often is a long-term condition, however, with appropriate diagnosis and treatment, it may be resolved in a matter of weeks.

So what is nummular eczema? How does it come about, what does it entail, and how does it affect one’s quality of life? Can it be resolved, if so, how, and in how much time? In this article, we will discuss this form of dermatitis and answer all the questions you may have!

Introduction

The American National Eczema Association defines nummular eczema as a form of localised dermatitis characterised by coin-shaped, itchy patches of skin, sometimes oozing fluid.¹ Nummular comes from the Latin ‘Nummus’ meaning coin. Nummular eczema more often affects men than women and around 0.2% of the population is estimated to be afflicted by this condition. The onset of discoid eczematous lesions can occur at any age, however highest onset is seen in individuals aged 50-65 years.² In the majority of affected individuals, some history of atopic eczema is associated with the disorder, however, this is not seen to be the case all the time, and often people with no history of any kind of eczema may also face this condition.

You might find such lesions on your skin, particularly on your legs, arms, neck or hands. While these may be symptoms of a condition other than discoid dermatitis/nummular eczema, in the following section we will discuss the symptoms characteristic of nummular eczema in particular.

Symptoms

Discoid dermatitis or nummular eczema, is characterised by a disc-shaped scaly patch of skin. These circular or oval-shaped lesions are erythematous in the initial stages, meaning they appear excessively red and fleshy due to the accumulation of blood and inflammation. Often the onset of such lesions is accompanied by a secretion of fluid. The condition affects the legs and feet most often, followed by the arms, hands, and torso, in that order. The face and scalp are not prone to nummular eczema.

In the initial stages, spots of unusually dry and bumpy skin develop in the affected region. These spots grow and converge into a larger dry, bumpy lesion. These then grow into swollen, cracked and scaly patches ranging from a few millimetres to a couple of centimetres in size.³

If you are light-skinned the patches may appear pink or redder than the skin around it, while if your skin is dark, the patches may either be paler than the skin around it or may have a dark brown shade. They often take on a violet tone, when present on the legs.

These scaly and sometimes blistered patches of skin often secrete pus-like fluid. This is usually a sign of infection from staphylococcus bacteria (the same bacteria suspected to be involved in other forms of eczema).⁴ The symptom which affects the quality of living most is the itching caused by this form of eczema, which tends to be more severe at night. Scratching or picking (excoriation) of the wound as a result of the itching sensation leads to worsening of the affected region.

Over time, the patch turns more dry and cracked and the secretion of fluid usually reduces. A major complication that arises is co-infection. The dry and eczematous patch may lose layers of skin, reducing the mechanical barrier function that the skin normally plays.⁵ As a result these regions are more prone to infection. Such infection is characterised by increased oozing of fluid, pus, and the formation of a yellow crust. Due to the body’s inflammatory response to infection, the affected region becomes swollen and the skin turns warm, red and sensitive. Severe infection may lead to the development of a fever.

In the later stages, these raised bumpy patches flatten as the condition subsides, however, the affected region often remains hyperpigmented or darker than the surrounding skin. Nummular eczema often returns to affect the same region, usually triggered by factors like: 

• Burns
• Dryness
• Soap or irritant
• Cold, dry weather⁶

However, experts maintain that with appropriate treatment nummular eczema, or discoid eczema/discoid dermatitis can be treated easily and resolved within a few weeks. 

Causes and Risk Factors

The cause of nummular eczema has not yet been narrowed down. There exist several potential triggers which seem to set off reactions involving the development of this condition, however, not much research has been conducted into investigating the mechanism of these triggers. While bacterial infection is often involved in the pathology of this disease, this is considered a secondary infection rather than a causative one.

Several factors have been suggested as reasons for the development of the disorder.⁷ Xerosis, a term used to define excessively dry skin (which may or may not be a symptom of another disorder), could be one reason, while airborne allergens have also been implicated. Factors responsible for compromising the skin’s natural moisture barrier may play a role in development, including frequent hot water showers or harsh soap. Similarly, exposure to certain metals, such as nickel sulphate, potassium dichromate, and cobalt chloride, which interfere with the cutaneous lipid barrier also may lead to susceptibility to developing this form of atopic dermatitis.^7,8

Other triggers may include stress, certain medication, contact allergy or hypersensitivity to something you may come in contact with, or even poor blood flow as seen in people with varicose eczema.^6,9 While eczema is suspected to have a genetic aspect, with research being conducted into specific genes thought to be associated with the development of the skin disorder,¹⁰ it is not known if nummular eczema has a genetic component or not. Atopic eczema is seen to run in families, with increased chances of developing a form of atopic dermatitis if one or both of your parents suffer from it.¹¹ Being a variation of atopic dermatitis, it is conceivable that nummular eczema too, runs in families. However further research must be conducted to confirm this.

Diagnosis

Clinical Examination

Diagnosis of nummular eczema involves clinical examination and characterization of the disorder based on its appearance and presentation, as well as dermoscopic examination (examination of the lesion, using a dermatoscope) to determine the depth, colour, and texture of the magnified affected region.⁷

Further testing may be done to rule out other possible diagnoses. For example, ringworm (Tinea corporis) presents similarly. Skin scrapings may be taken and examined at a cellular level to test for signs of other causative agents, including tinea corporis, or for signs of infection associated with atopic dermatitis such as the bacteria S. aureus.⁷

Diagnosis is usually done based on the presentation and characterisation of the lesion. Dermatologists may observe:

• The shape: coin-shaped, discoid, oval or circular patch of affected skin
• The size: 1 to 10 cm
• The colour: may be reddish and mucosal (erythematous) in initial stages, hyperpigmented in later stages
• The texture: rough, scaly and dry
• Signs of infection: infection may be likely if the lesion is oozing pus, swollen and sensitive, and possesses a yellowish crust⁷

In the case of secondary infection, your physician or dermatologist may take swabs for additional testing to identify the cause of the infection.

Differential Diagnosis

Ringworm or tinea corporis is a common differential diagnosis for nummular eczema due to the similarity in shape and general texture. However, ringworm presents with a clear middle and raised borders.⁷ Psoriasis is a similar inflammatory skin condition caused by an autoimmune response. Plaques or lesions characteristic of psoriasis are thicker and silvery.¹² Atopic dermatitis and other forms of eczema present with similar conditions, although usually lacking the coin-shape. These may sometimes be contagious, like contact dermatitis, so it is necessary to ensure correct diagnosis of the condition (by patch testing) is conducted by a certified professional.⁷

Treatment Options

Excessive dryness is a major factor that is thought to bring about discoid dermatitis as well as the itchiness and discomfort you may face as a result. Therefore you must keep the affected region well moisturised using moisturisers or emollients (products which essentially lock in moisture and maintain the softness of the skin), including petroleum jelly or hand cream.⁷

Your physician may prescribe topical corticosteroids like hydrocortisone. These are a type of anti-inflammatory steroid often used on skin affected by eczema. Your pharmacist will recommend that you use these products less than twice a day and for no longer than a week.

The severe itching caused by nummular eczema can be reduced by the use of low-potency antihistamines.⁷

Once properly diagnosed, nummular eczema can be resolved within a week or two simply with the right treatment, that being the appropriate application of topical corticosteroids as prescribed by your doctor, and maintaining moisturisation of your affected region.⁷ 

In some cases, secondary infection can occur due to bacteria or fungus entering the broken skin. This is diagnosed as mentioned above, by analysis of lesion scrapings/swabs. If positive for infection, your doctor will prescribe you appropriate topical antibiotics.⁷

Nummular eczema remissions may occur fairly often, over a period of months to a few years, with the lesions returning in the same regions. This remission is usually due to exposure to the various triggers and often occurs during cold and dry seasons. It is therefore essential to reduce exposure to such triggers. This can be done in the following ways:

• Avoid long showers or baths in very hot water
• To mitigate worsening of the condition due to irritants, gentle soaps are suggested, preferably hypoallergenic and hydrating products
• It is also recommended that you avoid tight clothing, and irritating or chafing fabric⁷

Summary

Nummular eczema (discoid eczema or discoid dermatitis) is a form of atopic dermatitis in which patients develop coin-shaped cracked and scaly lesions or dry patches. These lesions are often erythematous and swollen, and sometimes ooze with secretions in the initial stages. The breakdown of the skin’s moisture barrier in these patches may lead to secondary staphylococcus infections, worsening the condition, which is accompanied by intense itching and discomfort. 

Nummular eczema affects men more than women and occurs in an estimated 0.2% of the population. The cause of this condition is unknown, however, several potential factors have been identified including excessive dryness and irritants like harsh soap, burns, or insect bites. Diagnosis of nummular eczema can be done easily by eye or through dermoscopic evaluation by your GP. Once diagnosed, the condition can be resolved by keeping the region moisturised and periodically applying topical corticosteroids. Antibiotics may be prescribed in cases of secondary infection, and antihistamines can help to reduce the itching symptoms. 

Overall, the condition is easy to treat and can be resolved within a couple of weeks. However, remission may occur often, with the condition returning over a span of several months to years, on exposure to triggers or during cold, dry weather conditions.