The terms eczema and dermatitis are interchangeable, covering a wide variety of conditions from the child with atopic eczema to the adult with an allergy to cement.
If patients are told they have dermatitis they may assume that it is related to their employment with the implication that they may be eligible for compensation.
It is not unusual for industrial workers to ask “Is it dermatitis, doctor?”, meaning “is it due to my job?”
Clinical appearance
Eczema is an inflammatory condition of the skin characterised by groups of vesicular lesions with a variable degree of exudate and scaling.
In some cases dryness and scaling predominate, with little inflammation.
In more acute cases there may be considerable inflammation and vesicle formation, in keeping with the Greek for “to boil out”, from which the word eczema is derived.
Sometimes the main feature may be blisters that become very large.
Eczema commonly itches and the clinical appearance may be modified by scratching, which with time may produce lichenification (thickening of the skin with increased skin markings).
Also as a result of scratching the skin surface may be broken and have excoriations, exudate, and secondary infection.
Pathology
The characteristic change is oedema between the cells of the epidermis, known as spongiosus, leading to formation of vesicles.
The whole epidermis becomes thickened with an increased keratin layer.
A variable degree of vasodilatation in the dermis and an inflammatory infiltrate may be present. Types of eczema
The many causes of eczema are not consistently related to the distribution and clinical appearance.
In general there are either external factors acting on the skin producing inflammatory changes or it is an endogenous condition.
It is important to remember there can be more than one cause for example, in atopic eczema or varicose eczema on the ankle an allergic reaction may develop to the treatments used.
Atopic eczema affects mainly the flexor surfaces of the elbows and knees as well as the face and neck.
To a variable degree it can affect the trunk as well. The typical patient with atopic eczema is a fretful, scratching child with eczema that varies in severity, often from one hour to the next.
In the older child or adult, eczema is more chronic and widespread and its occurrence is often related to stress.
Atopic eczema is common, affecting 3% of all infants, and runs a chronic course with variable remissions.
It normally clears during childhood but may continue into adolescence and adult life as a chronic disease. It is often associated with asthma and rhinitis. Sufferers from atopic eczema often have a family history of the condition.
Variants of atopic eczema are pityriasis alba white patches on the face of children with a fair complexion and chronic juvenile plantar dermatosis dry cracked skin of the forefoot in children.
This does not affect the interdigital spaces and is not due to a fungal infection.
Eczema herpeticum.
Children with atopic eczema are particularly prone to herpes virus infection, which may be life threatening.
Close contact with adults with “cold sores” should therefore be avoided.
Nummular eczema appears as coin shaped lesions on legs and trunk. Stasis eczema occurs around the ankles, where there is impaired venous return.
Paget’s disease of the breast. Whereas bilateral eczema of the nipples and areolae occur in women, any unilateral, persistent, areas of dermatitis in this region may be caused by Paget’s disease, in which there is underlying carcinoma of the ducts.
In such cases a biopsy is essential.
Lichen simplex is a localised area of lichenification produced by rubbing. Neurodermatitis is a term often used synonymously with lichen simplex.
It is also used to describe generalised dryness and itching of the skin, usually in those with atopic eczema.
Asteatotic eczema occurs in older people with a dry, “crazypaving” pattern, particularly on the legs.
Pompholyx is itching vesicles on the fingers, with lesions on the palms and soles in some patients.
Infection can modify the presentation of any type of eczema or contact dermatitis.
Contact dermatitis
The skin normally performs its function as a barrier very effectively.
If this is overcome by substances penetrating the epidermis an inflammatory response may occur leading to epidermal damage.
These changes may be due to either (a) an allergic response to a specific substance acting as a sensitiser or (b) a simple irritant effect.
An understanding of the difference between these reactions is helpful in the clinical assessment of contact dermatitis.
Allergic contact dermatitis
The characteristics of allergic dermatitis are:
• Previous exposure to the substance concerned.
• 48–96 hours between contact and the development of changes in the skin.
• Activation of previously sensitised sites by contact with the same allergen elsewhere on the body.
• Persistence of the allergy for many years.
The explanation of the sequence of events in a previously sensitised individual is as follows:
The antigen penetrates the epidermis and is picked up by a Langerhans cell sensitised to it.
It is then transported to the regional lymph node where the paracortical region produces a clone of T cells specifically programmed to react to that antigen.
The sensitised T cells accumulate at the site of the antigen and react with it to produce an inflammatory response.
This takes 48 hours and is amplified by interleukins that provide a feedback stimulus to the production of further sensitised T cells.
Allergic contact dermatitis can be illustrated by the example of an individual with an allergy to nickel who has previously reacted to a wrist watch.
Working with metal objects that contain nickel leads to dermatitis on the hands and also a flare up at the site of previous contact with the watch.
The skin clears on holiday but the dermatitis recurs two days after the person returns to work.
Irritant contact dermatitis
This has a much less defined clinical course and is caused by a wide variety of substances with no predictable time interval between contact and the appearance of the rash.
Dermatitis occurs soon after exposure and the severity varies with the quantity, concentration, and length of exposure to the substance concerned.
Previous contact is not required, unlike allergic dermatitis where previous sensitisation is necessary.
Photodermatitis
Photodermatitis, caused by the interaction of light and chemical absorbed by the skin, occurs in areas exposed to light.
It may be due to (a) drugs taken internally, such as sulphonamides, phenothiazines, and dimethylchlortetracycline, or (b) substances in contact with the skin, such as topical antihistamines, local anaesthetics, cosmetics, and antibacterials.
Morphology
The clinical appearance of both allergic and irritant contact dermatitis may be similar, but there are specific changes that help in differentiating them.
An acute allergic reaction tends to produce erythema, oedema, and vesicles.
The more chronic lesions are often lichenified.
Irritant dermatitis may present as slight scaling and itching or extensive epidermal damage resembling a superficial burn, as the child in the illustration shows.
Pathology
The reaction to specific allergens leads to a typical eczematous reaction with oedema separating the epidermal cells and blister formation.
In irritant dermatitis there may also be eczematous changes but also non-specific inflammation, thickening of keratin, and pyknotic, dead epidermal cells.
The distribution of the skin changes is often helpful. For example, an itchy rash on the waist may be due to an allergy to rubber in the waistband of underclothing or a metal fastener.
Gloves or the rubber lining of goggles can cause a persisting dermatitis.
An irritant substance often produces a more diffuse eruption, as shown by the patient who developed itching and redness from dithranol.
An allergy to medications used for treating leg ulcers is a common cause of persisting dermatitis on the leg.
Patch testing
Patch testing is used to determine the substances causing contact dermatitis.
The concentration used is critical.
If it is too low there may be no reaction, giving a false negative result, and if it is too high it may produce an irritant reaction, which is interpreted as showing an allergy (false positive).
Another possible danger is the induction of an allergy by the test substance.
The optimum concentration and best vehicle have been found for most common allergens, which are the basis of the “battery” of tests used in most dermatology units.
The test patches are left in place for 48 hours then removed, the sites marked, and any positive reactions noted.
A further examination is carried out at 96 hours to detect any further reactions.
It is most important not to put a possible causative substance on the skin in a random manner without proper dilution and without control patches.
The results will be meaningless and irritant reactions, which are unpleasant for the patient, may occur.
Occupational dermatitis
Dermatitis, which is simply inflammation of the skin, can arise as a result of:
In the workplace, all three factors may contribute to dermatitis.
For example, a student nurse or trainee hairdresser is exposed to water, detergents, and other factors that will exacerbate any pre-existing eczema.
In addition, there may be specific allergies and, as a result of the broken skin, secondary infection can occur making the situation even worse.
The following points are helpful in determining the role of occupational causes.
• If the dermatitis first occurred during employment or with a change of employment and had not been present before, then occupational factors are more likely.
• If the condition generally clears during holidays and when away from the workplace, this suggests an occupational cause, but chronic irritant dermatitis may persist when the patient is away from the workplace.
• If there is exposure to substances that are known to induce dermatitis and protective measures are inadequate at the workplace then an occupational cause is likely.
• If secondary infection is present, this can keep a dermatitis active even when away from the workplace and sometimes allergen exposure continues at home; for example, an allergy to rubber gloves at work will also occur when rubber gloves are used for domestic work at home.
Whatever the cause of the dermatitis, the end result may seem the same clinically, because the inflammation and blisters of atopic eczema may be indistinguishable from an allergic reaction to rubber gloves.
Generally, contact dermatitis is more common on the dorsal surface of the hands whereas atopic eczema occurs on the palms and sides of the fingers.
Irritant contact dermatitis can occur acutely as mentioned above and there is usually a definite history of exposure to irritating chemicals.
Chronic irritant dermatitis can be harder to assess as it develops insidiously in many cases.
Often it starts with episodes of transient inflammation that clear up, but with each successive episode the damage becomes worse with an escalation of inflammatory changes that eventually become chronic and fixed.
Once chronic damage has occurred the skin is vulnerable to any further irritation, so the condition may flare up in the future even after removal of the causative factors.
Individuals with atopic eczema are particularly liable to develop chronic irritant dermatitis and secondary infection is an additional factor.
Allergic contact dermatitis occurs as an allergic reaction to specific substances.
As this involves a cell mediated response the inflammatory reaction occurs about two days after exposure and once the allergy is present further exposure will inevitably produce a reaction.
Some substances are much more likely to produce an allergy, such as epoxy resin monomer, than others, such as cement, which characteristically requires exposure over many years before an allergy develops.
In addition to the capacity of the substance to produce an allergic reaction, individuals also vary considerably in the capacity to develop allergies.
Immediate type sensitivity is sometimes seen as a reaction to food protein and sensitivity to latex gloves.
This can produce a very severe reaction, particularly in atopic individuals.
The itching skin (pruritus)
It is sometimes very difficult to help a patient with a persistently itching skin, particularly if there is no apparent cause. Pruritus is a general term for itching skin, whatever the reason.
Itching with skin manifestations
Eczema is associated with itching due to the accumulation of fluid between the epidermal cells that are thought to produce stretching of the nerve fibres.
As a result of persistent scratching there is often lichenification which conceals the original underlying areas with eczema.
Exposure to irritants and persistent allergic reactions can produce intense itching and should always be considered.
“Allergic reactions” due to external agents often cause intense itching.
Systemic allergic reactions such as a fixed drug eruption, erythema multiforme, and vasculitis are less likely to cause pruritus.
Psoriasis, which characteristically has hyperkeratotic plaques, usually does not itch but sometimes there can be considerable itching.
Occasionally this is due to secondary infection of breaks in the skin surface.
Lichen planus presents with groups of flat-topped papules which often cause an intense itch.
Blistering disorders of the skin may itch. In herpes simplex there is usually burning and itching in the early stages.
In herpes zoster there may be a variable degree of itching, but this is overshadowed by the pain and discomfort of the fully developed lesions.
By contrast, bullous impetigo causes few symptoms, although there may be extensive blisters.
Itching is usually not present.
Dermatitis herpetiformis is characterised by intense persistent and severe itching that patients often describe as being unendurable.
Usual measures such as topical steroids and antihistamines have little if any effect.
By contrast, the blisters of pemphigoid do not itch although the earlier inflamed lesions can be irritating. Parasites.
Fleas and mites cause pruritic papules in groups.
The patient may not realise that they may have been acquired after a walk in the country or encountering a dog or cat.
Nodular prurigo may develop after insect bites and is characterised by persistent itching, lichenified papules, and nodules over the trunk and limbs.
The patient attacks them vigorously and promotes a persisting “itch–scratch–itch” cycle which is very difficult to break.
Parasitophobia is characterised by the patient reporting the presence of small insects burrowing into the skin which persists despite all forms of treatment.
The patient will produce small flakes of skin, fibres of clothing, and pieces of dust, usually in carefully folded pieces of paper, for examination.
These should always be examined and the patient gently informed that no insect could be found but this will not be believed.
Treatment is therefore very difficult and sometimes recourse has to be had to psychotropic drugs.
Infestations with lice cause irritation and a scabies mite can cause widespread persistent pruritus, even though only a dozen or so active scabies burrows are present.
It is always acquired by close human contact and the diagnosis may be missed unless an adequate history of personal contacts and a thorough clinical examination is carried out.
However, a speculative diagnosis of scabies should be avoided.
Itching with no skin lesions
If no dermatological lesions are present generalised pruritus or itchy skin may indicate an underlying internal cause. In elderly patients, however, the skin may itch simply because it is dry.
Hodgkin’s disease may present with pruritus as a sign of the internal malignancy long before any other manifestations.
A 35 year old ambulance driver attended the dermatology clinic with intense itching but a normal skin and no history of skin disease.
His general health was good and both physical examination and all blood tests were normal.
However, a chest x ray examination showed a mediastinal shadow that was found to be due to Hodgkin’s lymphoma.
Fortunately this was easily treated.
Other forms of carcinoma rarely cause pruritus.
Metabolic and endocrine disease
Biliary obstruction and chronic renal disease cause intense pruritus.
Thyroid disease can be associated with an itching skin.
In hyperthyroidism the skin seems normal but in hypothyroidism there is dryness of the skin causing pruritus.
Blood diseases.
Polycythaemia and iron deficiency are sometimes associated with itching skin.
Treatment
Treatment of the cause must be carried out when possible.
Calamine lotion cools the skin with 0·5% menthol or 1% phenol in aqueous cream.
Camphor-containing preparations and crotamiton (Eurax) are also helpful.
Topical steroid ointments and occlusive dressings may help to prevent scratching and may help to break the itch–scratch–itch cycle.
Emollients should be used for dry skin.
Topical local anaesthetics may give relief but intolerance develops and they can cause allergic reactions.
Sedative antihistamines at night may be helpful.
In liver failure cholestyramine powder may help to relieve the intense pruritus, as this is thought to be due to bile salts in the skin.
Antihistamines can be helpful both for their antipruritic effect and because many are sedative and enable the itching patient to sleep.
Pruritus ani is a common troublesome condition and the following points may be helpful:
• Advise gentle cleaning once daily and patients should be advised to avoid excessive washing.
• Avoid harsh toilet paper, especially if coloured, because cheap dyes irritate and cause allergies.
Olive oil and cotton wool can be used instead.
• Weak topical steroids will help to reduce inflammation, with zinc cream or ointment as a protective layer on top.
• Anal leakage from an incompetent sphincter, skin tags, or haemorrhoids may require surgical treatment.
• There may be an anxiety or depression and prutitus ani itself can lead to irritability and depression.
Pruritus vulvae is a persistent irritation of the vulva which can be most distressing and is most common in postmenopausal women.
It is important to eliminate any factors that may be preventing resolution.
These include:
• Secondary infection with pyogenic bacteria or yeasts
• Eczema or contact dermatitis
• Lichen sclerosus atrophicus.
The adjacent vaginal mucosa should be examined to exclude an intraepithelial neoplasm or lichen planus.
Treatment includes suitable antiseptic preparations such as 2% eosin, regular but not excessive washing, emollients, and topical steroids, bearing in mind the possibility of infection.
