Overview
Discoid eczema, also known as nummular dermatitis, is a chronic inflammatory skin condition characterized by the formation of itchy, swollen, and cracked circular or oval patches on the skin. These lesions can vary in size, ranging from a few millimeters to several centimeters, and are most commonly found on the limbs, although they can occur anywhere on the body. Without timely intervention, the condition can persist for extended periods, often recurring in the same areas.
While the pathogenesis of discoid eczema remains largely unknown, it is closely linked to skin dryness, which compromises the skin’s natural barrier, making it more susceptible to irritation and infection. The condition is relatively common, especially among middle-aged and older adults, and can significantly impact quality of life due to its chronic nature and associated symptoms. This review will explore the causes, diagnosis, and treatment of discoid eczema, with a focus on current medical understanding and therapeutic approaches.
Causes of Discoid Eczema
The precise etiology of discoid eczema remains unclear, though several factors are thought to contribute to its onset and progression. One of the most prominent contributing factors is skin dryness, which can severely impair the skin’s ability to act as a protective barrier against environmental irritants and allergens. When the skin is excessively dry, substances that are typically harmless, such as soaps, detergents, and other chemicals, can irritate the skin and trigger an inflammatory response.
In addition to dry skin, environmental factors play a significant role in the development and exacerbation of discoid eczema. For example, cold and dry climates tend to aggravate the condition, while humid environments may alleviate symptoms. Individuals living in colder climates or those exposed to central heating for long periods are more prone to experiencing flare-ups. Furthermore, exposure to certain chemicals in cosmetics, toiletries, and household cleaners can act as irritants, triggering or worsening the condition.
Genetic and Immune System Factors
While discoid eczema is not typically considered a hereditary condition, individuals with a history of atopic eczema (atopic dermatitis) are at a higher risk of developing the condition. Atopic eczema, which is commonly associated with other atopic conditions such as asthma and hay fever, may share some underlying immune dysregulation with discoid eczema. However, unlike atopic dermatitis, discoid eczema does not seem to run in families.
The immune system’s role in the development of discoid eczema is an area of ongoing research. The condition is believed to involve both an overactive immune response and a compromised skin barrier, leading to chronic inflammation. In some cases, Staphylococcus aureus colonization or infection may be a contributing factor, as bacterial infections can exacerbate inflammation and delay healing. This bacterial association is more commonly seen in cases where the eczema becomes secondarily infected, resulting in increased oozing and crusting of the lesions.
Triggers and Risk Factors
Several factors may trigger an outbreak of discoid eczema. One of the most common triggers is localized skin trauma, such as an insect bite, scratch, or burn. These minor injuries can lead to the formation of eczematous plaques at the site of the trauma, particularly in individuals with predisposing factors such as dry skin or atopic dermatitis.
Other potential triggers include:
- Medications: Some medications, particularly those that cause skin dryness, have been linked to the onset of discoid eczema. Examples include certain diuretics and cholesterol-lowering drugs.
- Environmental conditions: Cold, dry climates can exacerbate discoid eczema, while warm, humid environments may provide relief. Central heating, prolonged exposure to dry air, and excessive bathing can also contribute to skin dryness and worsen symptoms.
- Chronic conditions: Individuals with varicose veins are at increased risk of developing discoid eczema on the lower legs, a condition known as varicose eczema. Additionally, chronic alcoholism in men has been associated with a higher prevalence of discoid eczema, likely due to the dehydrating effects of alcohol on the skin.
Diagnosis of Discoid Eczema
Diagnosis of discoid eczema is primarily based on clinical evaluation. The appearance of the characteristic circular or oval patches is typically sufficient for a dermatologist or healthcare provider to make a diagnosis. However, additional tests may be required to confirm the diagnosis and rule out other conditions that may present similarly.
Clinical Examination
A thorough physical examination is the first step in diagnosing discoid eczema. The dermatologist will look for the presence of well-defined, round, or oval patches of eczema, which may be swollen, blistered, oozing, or dry and scaly. The patches are most commonly found on the limbs but may occur on the trunk or elsewhere on the body. It is important to note that discoid eczema rarely affects the face or scalp.
Laboratory Tests
In some cases, laboratory tests may be necessary to confirm the diagnosis and rule out other skin conditions, such as fungal infections or psoriasis. The following tests may be conducted:
- Bacterial swabs: If infection is suspected, bacterial swabs may be taken to check for the presence of Staphylococcus aureus or other bacteria. This is particularly important in cases where the lesions are oozing or crusted, as secondary infection can exacerbate symptoms and delay healing.
- Skin scrapings for mycology: Skin scrapings may be taken for mycological analysis to rule out tinea corporis (ringworm), a fungal infection that can present with similar circular lesions. This is especially important in cases where the lesions appear ring-like, as fungal infections can be easily mistaken for discoid eczema.
- Patch testing: In chronic or recurrent cases of discoid eczema, patch testing may be conducted to identify potential contact allergens. This is particularly relevant if the eczema is thought to be triggered or exacerbated by contact with certain metals, such as nickel or chromate, which are common allergens in contact dermatitis.
Differential Diagnosis
Discoid eczema must be differentiated from other skin conditions that can present with annular or circular lesions. These include:
- Tinea corporis (ringworm): A fungal infection that causes round, red, scaly patches with central clearing.
- Plaque psoriasis: A chronic inflammatory skin condition characterized by well-defined, scaly plaques.
- Pityriasis rosea: A viral skin condition that presents with a herald patch followed by multiple smaller lesions, often in a Christmas-tree pattern on the trunk.
Treatment of Discoid Eczema
Discoid eczema is a chronic condition that often requires long-term management to control symptoms and prevent flare-ups. The main goals of treatment are to reduce inflammation, restore the skin barrier, relieve itching, and prevent secondary infections. Treatment strategies vary depending on the severity of the condition, and a combination of topical and systemic therapies may be required.
1. Emollients and Moisturizers
Emollients, also known as moisturizers, are the cornerstone of discoid eczema treatment. They help restore the skin’s natural barrier by providing a protective film that reduces water loss and protects the skin from irritants. Emollients should be applied frequently, even when the skin is not actively inflamed, to prevent dryness and maintain hydration. Common types of emollients include:
- Ointments: These contain a high proportion of oil and are particularly effective for very dry, thickened skin. However, they can be greasy and may not be suitable for use on the face or in areas prone to sweating.
- Creams and lotions: These are less greasy than ointments and are more suitable for inflamed or weeping areas. They are also easier to apply and are less likely to stain clothing.
Regular use of emollients is essential for managing discoid eczema. Patients should apply them after bathing, while the skin is still damp, to lock in moisture. In severe cases, emollients may need to be applied several times a day to prevent the skin from becoming dry and irritated.
2. Topical Corticosteroids
Topical corticosteroids are commonly prescribed to reduce inflammation and control flare-ups. Mild topical corticosteroids are typically used for sensitive areas like the face and neck, while stronger formulations may be necessary for thicker or more inflamed skin, particularly on the limbs or trunk.
The application of topical corticosteroids should be limited to the affected areas and used as directed by a healthcare provider to avoid potential side effects such as skin thinning (atrophy), changes in skin pigmentation, and the development of acne or increased hair growth in treated areas. Typically, corticosteroids are applied once or twice daily for a few weeks until the inflammation subsides. After the symptoms improve, patients are advised to reduce the frequency of use or switch to a milder formulation to minimize the risk of adverse effects.
3. Antibiotics
Secondary bacterial infection is a common complication of discoid eczema, particularly when the lesions become oozing or crusted. In such cases, antibiotics may be required to eliminate the infection and promote healing.
- Topical antibiotics: For localized infections, topical antibiotics such as fusidic acid may be applied directly to the affected areas. These medications are usually combined with a topical corticosteroid to simultaneously treat inflammation and infection.
- Oral antibiotics: If the infection is more widespread or severe, oral antibiotics such as flucloxacillin or clarithromycin may be prescribed. These are typically taken for one to two weeks, depending on the severity of the infection.
It is important to complete the full course of antibiotics as prescribed to ensure the infection is fully cleared and to prevent the development of antibiotic resistance.
4. Antihistamines
Antihistamines may be prescribed to alleviate the intense itching associated with discoid eczema, particularly if theitching disrupts sleep or leads to excessive scratching that worsens the skin lesions.
- Sedating antihistamines: Older antihistamines, such as diphenhydramine, may be used at night to help patients sleep by reducing itchiness. These medications can cause drowsiness, making them less suitable for daytime use.
- Non-sedating antihistamines: For daytime use, non-sedating antihistamines, such as cetirizine or loratadine, may be preferred to manage itching without causing drowsiness.
While antihistamines can help control itching, they do not address the underlying inflammation of discoid eczema. Therefore, they are typically used in conjunction with other treatments such as emollients and corticosteroids.
5. Phototherapy (Ultraviolet Radiation Therapy)
For patients with widespread or severe discoid eczema that does not respond well to topical treatments, phototherapy may be considered. Phototherapy involves exposing the affected areas of skin to controlled doses of ultraviolet (UV) light, which can help reduce inflammation, slow down the proliferation of skin cells, and alleviate itching.
- UVB phototherapy: This is the most commonly used form of phototherapy for discoid eczema and involves the use of narrowband UVB light. Treatment is typically administered two to three times per week for several weeks.
- PUVA therapy: In more severe cases, PUVA (psoralen and UVA) therapy may be used. This treatment involves the use of a photosensitizing medication (psoralen) followed by exposure to UVA light. PUVA therapy is more potent than UVB but carries a higher risk of side effects, including an increased risk of skin cancer with long-term use.
Phototherapy is generally reserved for patients who have not responded to standard topical treatments, and it is typically conducted under the supervision of a dermatologist.
6. Systemic Treatments
In cases of severe, persistent discoid eczema that does not respond to topical therapies or phototherapy, systemic treatments may be required. These medications work by suppressing the immune system to reduce inflammation throughout the body. Common systemic treatments for discoid eczema include:
- Oral corticosteroids: Systemic corticosteroids, such as prednisone, are sometimes prescribed for short-term use in severe cases of discoid eczema. However, long-term use of oral steroids is avoided due to the risk of serious side effects, including weight gain, high blood pressure, osteoporosis, and an increased susceptibility to infections.
- Immunosuppressants: Medications such as methotrexate, azathioprine, or ciclosporin may be used to manage chronic, refractory discoid eczema. These drugs require careful monitoring by a dermatologist due to their potential side effects, which include liver toxicity, bone marrow suppression, and an increased risk of infections.
Systemic treatments are typically reserved for the most severe cases of discoid eczema and are used under close medical supervision to minimize the risk of complications.
Self-Care and Preventative Measures
In addition to medical treatments, self-care measures are essential for managing discoid eczema and preventing flare-ups. These include:
- Regular use of emollients: Patients are advised to apply emollients several times a day to maintain skin hydration and restore the skin barrier. It is especially important to apply emollients after bathing, while the skin is still damp, to lock in moisture.
- Avoiding irritants: Soaps, detergents, bubble baths, and other harsh skin care products should be avoided, as they can strip the skin of its natural oils and exacerbate dryness. Instead, patients should use soap substitutes or mild, fragrance-free cleansers.
- Protecting the skin: Minor skin injuries, such as cuts, scrapes, or insect bites, can trigger flare-ups of discoid eczema. Patients are encouraged to wear protective clothing and gloves when engaging in activities that could potentially damage the skin.
- Lukewarm baths: Taking daily lukewarm baths or showers, rather than hot baths, can help soothe the skin without causing further dryness. Adding an emollient to the bathwater may also help reduce itching and maintain skin hydration.
It is important to avoid scratching the affected areas, as this can worsen the lesions and increase the risk of infection. Keeping fingernails short and clean can help reduce the risk of causing skin damage during scratching.
Complications of Discoid Eczema
While discoid eczema is generally a manageable condition, complications can arise if the condition is not properly treated. These complications include:
- Infection: As mentioned earlier, discoid eczema lesions can become infected, particularly if they are scratched or if the skin barrier is compromised. Signs of infection include increased oozing, the formation of a yellow crust, and the presence of localized heat, swelling, and tenderness. In severe cases, patients may develop systemic symptoms such as fever or malaise, indicating the need for prompt medical attention.
- Scarring and pigmentation changes: Over time, discoid eczema may lead to permanent scarring or changes in skin pigmentation. In individuals with darker skin tones, post-inflammatory hyperpigmentation (dark spots) or hypopigmentation (light spots) may persist for several months after the lesions have healed.
- Psychosocial impact: The visible nature of discoid eczema, particularly when it affects the hands, arms, or legs, can lead to significant emotional and psychological distress. Patients may experience anxiety, depression, or social withdrawal due to the appearance of their skin. Therefore, psychological support or counseling may be beneficial for individuals who struggle with the psychosocial impact of the condition.
Conclusion
Discoid eczema is a chronic and often distressing skin condition that requires a comprehensive approach to management. While the exact cause of the condition remains unclear, treatment strategies focus on restoring the skin barrier, reducing inflammation, and preventing secondary infections. Emollients, topical corticosteroids, and antibiotics are commonly used to manage symptoms, while more severe cases may require phototherapy or systemic immunosuppressants.
Self-care measures, including the regular use of emollients, avoidance of irritants, and skin protection, play a critical role in preventing flare-ups and maintaining skin health. Patients with discoid eczema should work closely with their healthcare providers to develop an individualized treatment plan that addresses their specific needs and reduces the risk of complications. Although there is no cure for discoid eczema, effective management can significantly improve quality of life and minimize the impact of the condition on daily activities.
References
Cleveland Clinic. (2023). Discoid eczema (nummular dermatitis): Symptoms, causes & treatment. Retrieved from https://my.clevelandclinic.org/health/diseases/22115-discoid-eczema-nummular-dermatitis
DermNet. (2023). Discoid eczema (nummular dermatitis). Retrieved from https://dermnetnz.org/topics/discoid-eczema
NHS. (2023). Nummular eczema (discoid eczema). Retrieved from https://www.nhs.uk/conditions/nummular-eczema
