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AlexanderSalava

Nummular Dermatitis

Nummular dermatitis (also known as nummular eczema and discoid eczema) is a common chronic form of eczema.
The diagnosis is based on the patient's history and clinical presentation.
Management consists of symptomatic treatment and prophylaxis.

The cause of nummular dermatitis is endogenous and multifactorial.
Children are likely to have nummular type infantile eczema Atopic Dermatitis in Children: Clinical Picture, Diagnosis and Treatment.
A great majority of patients have atopic diathesis.
Dryness of the skin is often a provoking factor in older patients (washing with soap and an abrasive brush, daily sauna use, swimming as a new hobby), injuries and wounds (leg ulcer) or lower extremity stasis dermatitis.
May rarely be provoked by drugs (TNF-alpha inhibitors, interferon, gold, retinoids).
Allergic contact dermatitis Allergic Contact Dermatitis may spread in the same manner as nummular dermatitis.
In some countries, the condition is misleadingly called infectious eczema, although no infectious aetiology can be shown (picture ).
The peak incidence is at the age of 40-60 years, more common in men than women.

Initially the patient develops a single papule or vesicle, around which increasingly more papules will form. They will then coalesce to form well-demarcated, round and usually highly pruritic lesions (pictures ).
Usually starts unilaterally on the lower legs or arms, but will later become symmetric.
Other typical sites are the thighs, arms, backs of the hands, extensor aspects of the upper limbs and the back.
The course of nummular dermatitis is chronic and relapsing with exacerbations.
The skin is often worse in the winter but improves with the summer sun.

Based on the patient's history and clinical presentation.
Fungal cultures of single lesions may be indicated to exclude tinea (fungal culture, microscopy of a plain specimen).
Bacterial culture usually grows Staphylococcus aureus, the clinical significance of which is debatable.
In prolonged and refractory disease histological examinations of skin biopsy.
Patch testing, as required, to exclude contact allergy Allergic Contact Dermatitis.

It may be difficult to differentiate between the different types of eczematous conditions. Even though similar features are often shared by atopic dermatitis and asteatotic eczema this will have no significant impact on the treatment.
Atopic dermatitis Atopic Dermatitis in Children: Clinical Picture, Diagnosis and Treatment: particularly in the young, manifests itself in patchy lesions. The history is important.
Asteatotic eczema: in elderly individuals, often starts in the lower legs and/or back
Stasis dermatitis Lower Leg Dermatitis: clinical signs of venous insufficiency
Allergic contact dermatitis Allergic Contact Dermatitis: has a patchy appearance, particularly if widespread
Psoriasis Psoriasis: sometimes impossible to differentiate from nummular dermatitis
Tinea Dermatomycoses: usually affects the feet, but may spread to the lower legs
Impetigo Impetigo and other Pyoderma: the clinical picture may overlap with that of an acute phase of nummular dermatitis.

Based on treating exacerbations and on prophylactic maintenance treatment.
Regular washing of the skin and the rash with a mild wash liquid
The regular application of basic topical ointments, particularly immediately after a wash, has been shown to reduce the number of exacerbations.
If the rash is weeping (picture ), wet wrap treatments may be used in addition to a glucocorticoid cream.
An adequately long treatment period with a moderately potent to potent glucocorticoid cream, for example once daily at night for 2-4 weeks, thereafter once or twice a week for 1-2 months as required.
Combination creams containing antiseptics/antimicrobials and a glucocorticoid may also be tried.
Tacrolimus cream is also potentially effective in the treatment of nummular dermatitis, particularly in atopic individuals.

Antimicrobials are very rarely needed in nummular dermatitis.
Antimicrobials or other systemic treatments are not the first-line treatments, and they do not replace topical treatment.
If secondary infection arises from the dermatitis (impetiginisation), systemic antimicrobials may be indicated, e.g. cephalexin 500 mg 3 times daily or floxacillin 750-1 000 mg 3 times daily for 7-10 days. Antimicrobials and their doses are the same as those used in impetigo Impetigo and other Pyoderma.
Oral glucocorticoids may be considered as short term treatment in a severe exacerbation, for example prednisolone 20-40 mg in the mornings for 1-2 weeks. Particularly effective against acute vesicular dermatitis, but is of no benefit in chronic dermatitis.
Non-drowsy antihistamines with normal or larger than normal doses may help especially patients with underlying or additional allergic symptoms, such as urticaria or allergic rhinitis. These can be used in addition to topical treatment and the dose is titrated according to the response, e.g. cetirizine 10 mg 1-2 tablets once or twice daily. Note: special requirements concerning the prescription may apply if the dosage exceeds 1 tablet per day.
At night, as necessary, sedative antihistamines, e.g. hydroxyzine 25 mg once or twice daily.

Treatment-resistant and chronic nummular dermatitis may warrant a verification of the diagnosis in specialized care and an evaluation of possible contact allergies.
Treatment alternatives in widespread dermatitis include light treatment (UVB or SUP therapy) and systemic immunosuppressive agents (under the supervision of a dermatologist).
Treatment response may show great variation, and the disease may reactivate after many years of remission.

Silverberg JI, Hou A, Warshaw EM, et al. Prevalence and trend of allergen sensitization in patients with nummular (discoid) eczema referred for patch testing: North American Contact Dermatitis Group data, 2001-2016. Contact Dermatitis 2021;85(1):46-57. [PubMed]
Leung AKC, Lam JM, Leong KF, et al. Nummular Eczema: An Updated Review. Recent Pat Inflamm Allergy Drug Discov 2020;14(2):146-155. [PubMed]
Tanaka T, Satoh T, Yokozeki H. Dental infection associated with nummular eczema as an overlooked focal infection. J Dermatol 2009;36(8):462-5. [PubMed]