Atopic eczema

Atopic eczema is the commonest skin disorder of childhood, affecting between 10% and 20% of school age children in the UK. The aetiology is a combination of genetic, environmental and immunological factors.

The term ‘atopy’ describes an exaggerated propensity to form IgE to common allergens. In later life, approximately half of eczema patients will develop associated atopic disorders such as asthma and allergic rhinitis. The molecular pathology in atopic eczema is complex. The epidermal Langerhans cells have high-affinity IgE receptors through which the T-helper cells (T_h2 and T_h1) release cytokines and mediate skin inflammation.

Atopic eczema is diagnosed clinically and the criteria for definition include chronic itchy skin with three or more of the following: a history of flexural involvement of the skin creases, visible flexural involvement, dry skin, other atopic disease or onset within the first 2 years of life. The clinical course and distribution change through puberty and adulthood. In infants, common areas affected are face, neck and nappy area. Through childhood, flexural sites such as folds of the elbows and backs of the knees are classically involved (see Fig. 57.3). Symptoms usually improve with age and approximately 60% have resolution of symptoms by the age of 16.

Fig. 57.3 Flexural eczema in childhood

(courtesy of M. Carr).

Exacerbating factors

A number of factors can aggravate atopic eczema:

• Extremes of temperature

• Irritants: soap, detergents, shower gels, bubble baths and water

• Stress

• Infection, either bacterial or viral

• Contact allergens

• Food allergens

• Inhaled allergens

• Airborne allergens.

The commonest trigger in the paediatric population is secondary infection, either bacterial or viral. Bacterial colonisation is common on the skin of those with atopic dermatitis and may result in the invasive infection triggering an acute flare. Staphylococcus aureus and Streptococcus spp. are most often responsible (Fig. 57.4).

Fig. 57.4 Impetigo complicating atopic eczema

(courtesy of M. Carr).

Viral infections such as herpes simplex and molluscum contagiosum may also complicate atopic eczema. Eczema herpeticum is caused by the widespread dissemination of herpes simplex virus in eczematous skin and is a dermatological emergency. It requires urgent assessment and treatment with systemic aciclovir.

In some cases of severe atopic eczema, food allergy may be a contributory factor, particularly if a clear temporal relationship is detected by the parents. These cases should be referred to a paediatric allergy specialist, with access to a paediatric dietician, as unsupervised dietary restriction should be avoided in children. Most children tend to grow out of food allergies over time with the exception of nut and shellfish allergies.

Contact dermatitis

Contact dermatitis is classified as either allergic contact dermatitis (ACD) or irritant contact dermatitis (ICD).

Irritant contact dermatitis

This is the most common form of occupational dermatitis and the commonest cause of hand eczema (Fig. 57.5). Unlike ACD, ICD is not immunologically mediated. The mechanism involves disruption of the epidermal permeability barrier and a direct cytotoxic effect depending on the irritant. Patients with pre-existing epidermal barrier dysfunction such as atopic eczema are at higher risk. The occupation of the individual may also be a risk factor, especially those working as builders, hairdressers, gardeners, healthcare workers and chefs. Irritants include detergents, oils, water, inorganic acids, alcohols and plastics. Preventative skin care is key and this includes the use of barriers such as emollients or cotton gloves in addition to avoiding suspected irritants.

Fig. 57.5 Contact dermatitis to cement in a building worker

(courtesy of M. Carr).

Seborrhoeic dermatitis

This common disorder is usually confined to areas with high sebum production. The likely aetiological mechanism is overgrowth of the commensal yeast Malassezia furfur (Pityosporum ovale). The clinical features are pink-yellow greasy patches with ‘bran-like’ scale which occur in the sebaceous-rich scalp, nasal folds, medial eyebrow, pre-sternal region and flexural sites. In the first few months of life, it manifests as coherent scaling of the scalp with inflammation and ooze, known as ‘cradle cap’. In adults, the symptoms are usually mild with a chronic, relapsing course. Extensive and severe seborrhoeic dermatitis can be seen in patients with underlying HIV infection or Parkinson’s disease. Treatment usually includes topical imidazoles.

Discoid eczema

Discoid eczema is also known as ‘nummular dermatitis’ and is a type of chronic eczema presenting with disseminated coin-shaped eczematous lesions of the extremities. Middle-aged males are most commonly affected.

Stasis eczema

Stasis eczema is also called stasis dermatitis, gravitational dermatitis or varicose eczema. It is a clinical component of chronic venous insufficiency seen in addition to other features which include varicose veins, skin discolouration, peripheral oedema, leg discomfort and non-healing ulcers. Clinical features include scaly eczematous plaques confined to the lower legs. Multiple topical medicines and dressings often lead to a secondary ACD. Management of stasis eczema should address the underlying cause.

Asteatotic eczema

Asteatotic eczema, also called eczema craquele, usually affects the lower legs and appears as dry, cracked skin likened to ‘cracked paving’. This is associated with increasing age, low humidity and frequent bathing. Treatment consists of emollients and mildly potent topical steroids.

Emollients

Emollients, topical hydrating agents consisting of fat or oil to soften the skin, are the mainstay of eczema management. Emollients are effective first-line treatments for all types of eczema, and regular, liberal use will reduce topical steroid requirements. The greasier products have more emollient effect (see Fig. 57.6). They are often underused and the need to educate the patient regarding use of sufficient quantities is vital. Dry skin is aggravated by soap and bath products, and therefore an emollient soap substitute for washing is advisable.

Fig. 57.6 Commonly used emollients used in dry skin conditions

(adapted from MeReC, 1998).

Topical corticosteroids

Topical steroids act as anti-inflammatory agents and are extremely useful and important in managing eczema. In recent years, the public have veered from overuse of topical steroids causing long-lasting side effects, to high levels of anxiety regarding possible side effects concerning their use. This can commonly lead to under treatment in children. Therefore, patient/carer education regarding appropriate topical steroid use is a crucial part of eczema management.

Topical steroids are classified into four main groups according to potency: mild, moderately potent, potent and very potent (Table 57.2). The choice of topical steroid is dependent on the site and severity of skin disease. Potent and very potent steroids should be avoided on delicate sites such as the face, genitals and flexures. The periorbital region should be treated with caution due to the thin skin increasing the likelihood of absorption and risk of cataracts or glaucoma. Treatment should be reviewed regularly and tailored accordingly. It is also important to remember that any form of occlusion will increase the absorption of steroid applied.

Side effects are mainly local and include striae (stretch marks), telangiectasia (visible dilated small blood vessels), epidermal thinning, purpura (bruising), acne and perioral dermatitis. Lower frequency side effects include poor wound healing, spread or worsening of untreated infections and hypertrichosis. Hypopigmentation is a temporary side effect of long-term topical steroid use and is frequently exploited in illegal ‘skin bleaching’ agents. Rarely, adrenal suppression or Cushing’s syndrome due to systemic absorption may occur.

Local and systemic side effects are extremely rare with appropriate use and duration of topical steroid treatment. Patients should be advised to spread preparations thinly either once or twice daily. The recommended amount used can be quantified using a fingertip unit (Fig. 57.7). The quantity in this unit is sufficient to cover an area the size of two adult palms. Table 57.3 details the quantities for application to different sites required for twice-daily treatment for 1 week.

Fig. 57.7 Recommended amount of a topical steroid corresponding to one fingertip unit.

Calcineurin inhibitors

The past decade saw the introduction of topical calcineurin inhibitors for the treatment of chronic eczema. These non-steroid immunomodulators inhibit calcineurin phosphatase which is important in T-lymphocyte activation. The main side effect is burning or stinging on initial application, but this usually improves after a few days. Although a theoretical risk of increased malignancy exists with these agents, studies have not shown an association between exposure to topical calcineurin inhibitors and increased rates of cutaneous malignancy. Calcineurin inhibitors should not be used on infected skin and are generally not very useful in severely inflamed eczematous skin. Their greatest value appears to be in maintenance therapy.

Tacrolimus ointment (Protopic®) is a calcineurin inhibitor derived from the oral transplant medicine FK506. The 0.1% and 0.03% preparations are indicated in the treatment of moderate to severe atopic dermatitis in adults and children over the age of 2 years. Tacrolimus is now also used in clinical practice as a second-line agent for other steroid responsive dermatoses.

Pimecrolimus 1% cream (Elidel®) is indicated for short-term or intermittent long-term use in mild to moderate atopic dermatitis. Studies have shown that it is effective, well tolerated and has minimal adverse effects in the long-term control of eczema in children aged over 2 years (Langley et al., 2008). Furthermore, this has resulted in the reduced use of topical steroids leading to a lower risk of steroid-induced side effects (Kapp et al., 2002).

Antihistamines

Pruritis is the most distressing feature of eczema. Oral antihistamines have no direct effect on pruritis in eczema; their main effect is sedation. Sedating antihistamines may cause day time drowsiness, and caution should be taken when driving and also if prescribed to school age children.

Topical imidazoles

Ketoconazole as a shampoo or cream is effective in reduction of Pityosporum ovale on the skin and is therefore useful in the treatment of seborrhoeic dermatitis. As the disease runs a chronic, relapsing course regular or intermittent use is usually necessary.

Coal tar preparations

Tar creams and ointments can be used in the management of hyperkeratotic, lichenified eczema. These are less cosmetically acceptable than other topical preparations, but coal tar is an effective anti-pruritic.

Bandaging

In children with atopic eczema, occlusion with bandages is useful to prevent scratching and potentiate the action of ointments and creams on the skin. Wet wrapping involves the application of emollients and steroids under a double layer to keep the inner layer moist. Parents can be trained to apply these bandages at home.

Systemic therapies

Phototherapy

Phototherapy can be effective in select cases of atopic dermatitis. Narrow-band UVB is the therapy of choice (Gambichler et al., 2005; Meduri et al., 2007). The potential side effects of all types of phototherapy include burning, premature ageing and a small increased risk of skin cancer. A small proportion of patients have photosensitive eczema, and this should be determined by taking a detailed patient history before prescribing phototherapy treatment. A treatment course requires a patient to attend two or three times a week for at least 6 weeks.

Dietary supplements

Current evidence suggests that probiotics are not an effective treatment for eczema and may carry a small risk of adverse events such as infection and small bowel ischaemia. There is no evidence for use of evening primrose oil. The use of Chinese herbal medications in atopic eczema is under close scrutiny, and conflicting results have been obtained. Liver function should be monitored as hepatitis is a known side effect of some Chinese herbal medicines.

Interactions with drugs used in the treatment of eczema and psoriasis are shown in Table 57.4.

Table 57.4 Interactions with drugs used in the treatment of eczema and psoriasis