HISTORY AND EXAMINATION

A careful history and full examination of the dermatological patient is essential. First, establish the duration and evolution of a rash as this will provide the basis for further questions and investigations. For example, a lesion may have been present from birth, or have developed in the past few days or weeks. Rashes may precede or coincide with other events such as intercurrent illnesses, a course of drugs, contact with animals, chemicals or plants or perhaps travel abroad. There may have been a previous episode of a similar rash or someone else in the family may recently have had a similar problem.
The appearance and distribution of a rash are also commonly characteristic in many conditions. Often a rash will start with a typical lesion and then spread in a particular pattern, as for example the herald patch of pityriasis rosea. Lesions may be confined to one body site, such as the face in acne rosacea, or to light-exposed sites or to a group of sites such as scalp, eyelid and eyelashes, face and chest in seborrhoeic dermatitis. 'Psoriasis characteristically affects the extensor surfaces of limbs, .whereas atopic dermatitis affects the flexor surfaces. Some i rashes, such as erythema multiforme, tend to have peripheral lesions first, affecting hands and feet before moving centrally. %Rashes may be symmetrical, more suggestive of an endogenous cause, or asymmetrical, when exogenous factors may be relevant. If a rash settles during a vacation, only to recur on return to work, a factor at the work site may be important.
An accurate description of the skin lesion is essential. The morphology of a lesion should be defined carefully as macular, papular, pustular or nodular. The presence of scale or crust, the colour of both recent and fading lesions, the presence of background sun damage in the form of wrinkles and skin thinning, abnormal pigmentation, changes in colour and distribution of hair all combine to make a characteristic picture that can often provide more information than subsequent investigations.
Finally the rash may be symptomatic: pain or pruritus are the most common symptoms. Painful lesions suggest active inflammation or infection; pruritus is very common and subjective, but can be useful in making a diagnosis. For example, the sudden onset of an itchy rash, worse at night, in a person with no previous skin problems is highly suggestive of scabies - but look for the characteristic lesions before making a diagnosis. Itch can be distressing, causing embarrassment and loss of sleep, and should be acknowledged sympathetically. Pain can precede the development of either herpes simplex or zoster lesions.
General health is also important. Many skin conditions are a reflection of underlying systemic conditions, so attention to a history of other illnesses, a brief systemic inquiry and recognition of other factors, such as arthritis, anaemia, weight gain or loss, thyroid enlargement, lymphadenopathy, all form part of the examination of the skin.

INVESTIGATIONS

SKIN BIOPSY

Skin biopsy is a useful and common investigation, as the histology of a lesion will establish, confirm or refute the clinical diagnosis in most cases. The biopsy should be well planned; early lesions are more informative as secondary infection or excoriation in mature lesions may mask underlying changes. A representative lesion should be selected, with attention to local anatomy, healing and potential scar formation. Although a punch biopsy is adequate for some conditions, an ellipse of skin, including normal and abnormal skin, is usually preferable (2.1).

2.1 Excision biopsy of a lesion on the leg. The ellipse for excision is I placed in the direction of the skin-crease line, and a small margin of normal skin is removed with the lesion.

The size and depth of biopsy depend on the nature of the lesion and the investigations required, but most biopsies should include dermis down to subcutaneous fat. Tissue should be sent for bacterial or viral culture, for routine histology (2.2) or for immunofluorescence staining (2.3, 2.75, 2.79, 3.11). Special stains, for example for fungal elements, should also be requested.

 SAMPLES FOR MICROBIOLOGICAL INVESTIGATIONS

Swabs can be taken from lesions with exudate or pus; blister fluid can be aspirated for culture or microscopy for bacterial or viral infection. Interpreting results requires some knowledge of commensal organisms and potential pathogens (2.4). Blood samples may be needed for culture, ASO titres, fluorescent treponema antibody-absorption (FTA-ABS) tests, paired samples for viral titres or serology for other infections such as viral hepatitis or HIV infection.
Fungal elements are found in keratin from nail clippings, hairs and skin scrapings. Examination under Wood's lamp is occasionally helpful in identifying fungal infections (Microsporon species fluoresce blue-green, Erythrasma pink; 2.5, 2.6). The affected skin should be scraped firmly, using a scalpel blade held at 45 degrees to the skin surface. Scrapings are collected in a fold of black paper or on microscope slides; adequate quantities are required for both microscopy and culture. Direct microscopy of skin scrapings treated with potassium hydroxide may reveal fungal hyphae and spores (2.7), and culture allows identification of the dermatophyte species. Scabies infestation may, be confirmed by looking for adult Acaris in skin scrapings (2.8).

2.2 & 2.3 Skin biopsy yields valuable information in many dermatological disorders. This patient has dermatitis herpetiformis (DH). A formalin-fixed perilesional biopsy (H&E stain) shows a papillary tip microabscess (arrow), which is typical of DH (2.2). Immunofluorescence on an unfixed section (2.3) shows IgA deposition in the papillary tips (arrows). These abnormalities occur at the level at which the subepithelial split subsequently develops in this blistering condition.

2.4 Skin commensals and common pathogens.

PATCH TESTING

Patch testing is designed to detect delayed hypersensitivity, or cell-mediated immune reactions, which may be the basis of an inflammatory rash. A careful history is very important for this investigation to be worthwhile. The patient may need to supply materials from suspect cosmetics, footwear or industrial processes. A visit to the work site of patients with suspected industrial dermatitis can be helpful. For this test, the suspect allergens are applied to the skin surface, using defined concentrations mixed in a paraffin ointment, under a special chamber (2.9, 2.10). After 72 hours a positive test shows erythema and blistering at the contact site (2.11, 2.12). A vast range of potential allergens exists; choosing the correct `battery' of test substances depends on the history, nature of the rash and knowledge of potential sensitizers (2.13). A standard battery of common sensitizers is available, together with extra lists, for example for patients with leg ulcers or chronic otitis externa, or for hairdressers; a range of common facial sensitizers, plant allergens or medicaments and bases of common topical therapies may be indicated. In recent years, contact dermatitis to topical steroids has been increasing and should be considered in patients who have used a wide range of preparations, usually over many months. Immediate contact patch tests for allergens suspected of causing urticarial reactions are occasionally helpful. The suspect allergen is applied directly to the skin and left on, unoccluded, for 30 minutes. An urticarial weal developing at the site of the allergen indicates a positive reaction. Photopatch testing involves the application of a suspected topical allergen together with ultraviolet irradiation. A range of wavelengths of ultraviolet may be used and nonirradiated control tests are included.

2.5 & 2.6 Wood's light is a long-wave ultraviolet light (UVA), which is useful in evaluating a range of skin conditions. In this patient, a superficial fungal infection of the scalp fluoresces blue-green (2.5). The appearance of the scalp of the same patient in normal light is shown in 2.6. The patient has ringworm (see p. 100).

2.7 Fungal hyphae in skin scrapings can be clearly seen microscopically after treatment of the scrapings with KOH.

2.8 Scabies mite. The discovery of even a single mite or egg seen microscopically in skin scrapings confirms the diagnosis.

2.9 Preparation for patch testing. Common sensitizers are dissolved in water or soft paraffin ointment and applied in sequence to special aluminium chambers (Finn chambers).

2.10 Patch testing. The aluminium chambers are mounted on hypoallergenic tape and applied to the back.

2.11 Positive patch test results in a gardener who became sensitized to chrysanthemums and other plants and developed contact dermatitis.

2.12 An extreme positive patch test reaction in close-up. There is extensive erythema and vesiculation. Ulceration may subsequently occur at the site. This patient reacted to rubber additives; she was a dental surgeon who developed severe contact dermatitis after wearing latex gloves.

IgE AND RADIOALLERGOSORBENT TESTS

IgE is often but not always raised in atopic dermatitis, but does not reflect severity of rash or response to treatment. More often a raised level is due to associated asthma. Radioallergosorbent tests (RASTs) record levels of specific IgE, indicating potential sensitizers such as animal dander, house-dust mites and a range of other potential inhaled or ingested sensitizers.

OTHER DIAGNOSTIC SKIN TESTS

Skin-prick tests with allergen extracts result in immediate (type 1) skin reactions; in atopic dermatitis frequent false positives occur and the test is more useful for hayfever or asthma sufferers (see p. 167).
Mantoux (p. 46) and Kveim (p. 198) tests require intradermal antigen injection, with tests read (and biopsied) at appropriate intervals.
OTHER INVESTIGATIONS

Haematological and biochemical tests are frequently used in primary skin disorders and the dermatological manifestations of systemic disease, and to monitor drug therapy with, for example, methotrexate, retinoids, dapsone or cyclosporm. Immunological investigations, including antinuclear antibody, immune complexes, complement levels and autoantibodies, may be required. Underlying medical or surgical problems should be investigated appropriately.

PSORIASIS

Psoriasis is a common disorder affecting around 2% of the population. The onset may be at any age, with peaks around 20 and 60 years. Men and women are affected equally. A positive family history is found in 30% of patients; in those developing the disease at an earlier age there is an'increased association with HLA CW6. The disease is characterized histologically by abnormal keratinocyte differentiation and hyperproliferation with inflammation, involving both lymphocytes and polymorphonuclear leucocytes and an associated vasodilatation of superficial dermal vessels. Investigations into the inherited basis of this disorder are complicated by genetic heterogeneity and to date no gene has been characterized. Environmental factors such as infection are also important.
Clinically, psoriasis is characterized by variability and unpredictability. The rash may be intermittent, undergospontaneous remission or be lifelong. In general a chronic condition, it may flare acutely and, rarely, be life-threatening. Patients generally feel well but they can experience considerable emotional distress and social isolation. There is an association between the severity of psoriasis and alcohol intake.
The most common presentation is chronic plaque psoriasis, generally affecting extensor surfaces in a symmetrical pattern (2.14, 2.15, 3.54). Lesions are clearly demarcated erythematous plaques covered with coarse scales that may be removed by gentle scraping (2.16). Involvement of flexures, especially inframammary or groin areas (2.17), is also common. In these sites the rash is not usually scaly and is often confused with fungal or yeast infections. The scalp may be involved alone or with other lesions; psoriasis in the scalp may be both `felt' and seen. The hairline (2.18) and behind the ears are common sites. A resistant plaque in the sacral area is also very common. Involvement of nails may be as coarse `pitting' as on a thimble (3.5) or as onycholysis (2.19) or gross thickening of the nail with underlying hyperkeratosis.
Guttate psoriasis is an abrupt onset of psoriasis with dropletshaped erythematous scaly lesions scattered widely over trunk and limbs with no predeliction for extensor surfaces (2.20). It may be triggered by a preceding streptococcal throat infection, and is more common in children and young adults. It usually clears completely but classic psoriasis may appear in later life.
Erythrodermic psoriasis (2.21) can be a life-threatening condition. The rash starts as common psoriasis but spreads to become confluent and often indistinguishable from other forms of erythroderma.
Arthropathy occurs in 10-15% of psoriasic patients. Classically, distal interphalangeal joints (3.55) and large joints such as ankles and knees are involved and the rheumatoid factor is negative. Rarely, the arthritis can be severe, producing an `arthritis mutilans' of the hands and feet with resultant severe disability (3.56, 3.57).
Localized chronic pustular psoriasis may occur without other evidence of psoriasis (2.22, 3.58). Generalized pustular psoriasis is a rare presentation that may be fatal. It may be precipitated by topical or systemic steroid use, drug reactions or infections. Crops of sterile pustules occur, with fever and systemic upset.
The treatment of psoriasis depends upon its location and severity but may involve topical emollients, dithranol, tar or steroids. Ultraviolet B radiation alone, and ultraviolet A radiation combined with an oral psoralens (PUVA) are often effective for widespread disease, but systemic treatment with retinoids, methotrexate, cyclosporin A or other drugs may be necessary for stubborn disease.

2.14 Psoriasis affecting the extensor surfaces of the arms. Other plaques are visible on the trunk.

2.15 Psoriasis on the extensor surface of the elbow.

2.16 Psoriasis. Typical small plaques, showing typical silvery scales. These can be removed by gentle scraping with a spatula or fingernail.

2.17 Psoriasis caused severe pruritus in this man. The discoloration of the lesions results largely from tar therapy.

2.18 Psoriasis of the scalp and hair margin. The patchy nature of scalp involvement helps to distinguish psoriasis from other conditions, such as dandruff and seborrhoeic dermatitis.

2.19 Psoriasis affecting the nail, causing pitting, onycholysis, discoloration and thickening.

2.20 Guttate psoriasis in a 17-year-old. The condition resolved completely within a few months.

2.21 Erythrodermic psoriasis is potentially lifethreatening, and it closely resembles other forms of erythroderma in which the whole skin surface is involved. The management of patients with severe erythroderma is as urgent as that of a patient with severe burns.

2.22 Pustular psoriasis of the palms. The palms and soles are the most common areas for this localized form of psoriasis. The pus is usually sterile, and the hands are not tender or oedematous.

DERMATITIS

Dermatitis and eczema are synonymous; in practice, the term eczema is usually restricted to dermatitis seen in atopic individuals. Dermatitis means inflammation in the skin. It may be acute with weeping, crusting and vesicle formation, subacute, or chronic with dryness, scaling and fissuring and lichenification (especially in atopic individuals; 2.23). The rash is almost always itchy and secondary infection is common. Dermatitis may be exogenous (contact, irritant, infective or photodermatitis) or endogenous (e.g. atopic, seborrhoeic, discoid). Most often the diagnosis can be established by the distribution pattern and morphology of the rash together with a detailed history.
Atopic dermatitis begins in childhood, between 2 and 6 months of age, affecting around 2% of the population, although the incidence does appear to be increasing. A family history of atopy is present in 70% of cases. Hayfever and solidus or asthma may develop as the child gets older. Over 90% of children are clear by the age of 12 years, but predicting this for an individual child is difficult. Few patients with the classic features are seen beyond the age of 30 years. In infants the face, neck and trunk are involved (2.24), with sparing of the napkin area. Flexural involvement appears later, behind knees, elbows, wrists and ankles (2.25) and lichenification may result from repeated scratching (2.23, 2.91). Hand dermatitis is common in later years. Secondary infection is common (2.26). Itch can be severe and causes much distress to patients and families. Food allergy, especially to eggs, fish and dairy products, may be relevant in some patients, but few benefit from exclusion diets. A number of abnormalities may be detected in the skin in atopic dermatitis, but the underlying mechanisms are still unclear. Immunological abnormalities include a tendency to increased IgE levels, a predisposition to anaphylactic reactions, increased skin reactivity to skin-prick tests and a reduction in local cell-mediated immunity; the latter leads to an increased tendency to viral infections such as molluscum contagiosum, viral warts and herpes simplex, and a reduced incidence of contact dermatitis. Changes in essential fatty acid metabolism have been described and some patients benefit from gammalinoleic acid supplements in the diet. Minor degrees of ichthyosis and keratosis pilaris are commonly seen; the skin is generally dry, with increased transepidermal water loss and a reduced resistance to irritant substances.
Neurodermatitis or lichen simplex is a localized chronic dermatitis, perpetuated by the itch-scratch cycle. Common sites are the nape of neck or lower leg (2.27). The pruritus is often disproportionate to the rash and lichenification is common. The initial cause of the rash is often not established and the condition can be difficult to treat. There may be clinical overlap between this condition and chronic nodular  prurigo, which is characterized by multiple small irritable patch widely scattered over the body (2.28).
Discoid dermatitis is characterized by discrete circular or oval patches of dermatitis in a symmetrical pattern often on extensor surfaces, almost always in adults. Exogenou causes should be excluded but often no cause is found (2.29)
Pompholyx is a variant of eczema in which recurrent vesicles or bullae affect the palms (2.30) and fingers, or soles, or both. It is characterized by remissions and relapses, which are sometimes provoked by heat, emotional stress, or an active fungal infection of the feet. There have been reports that the ingestion of small amounts of nickel in susceptible patients may trigger
an attack.
Contact dermatitis is an allergy (type IV, delayed hypersensitivity) to a substance present on the skin surface. The relevant factor may be immediately obvious - for example nickel, perfume, shoe rubber or plants (2.31-2.33). A wide range of potential allergens exists in domestic and industrial life; a careful history and relevant patch tests should establish the diagnosis. The rash can be chronic, patchy and some distance from the allergen, for example nail varnish allergy may present with dermatitis on the face or neck.
Stasis dermatitis is associated with venous insufficiency. It is often complicated by oedema, infection, ulceration and contact dermatitis to topical medicaments or bandages (2.34). A secondary, widespread symmetrical dermatitis may develop. Seborrhoeic dermatitis occurs in infancy as cradle cap, with scattered erythematous patches on the head and neck and an associated napkin rash (2.35). In adults, scaling in the scalp,blepharitis, red scaly patches in nasolabial folds (2.36), around the ears and on the presternal area are characteristic; intertrigo may occur. It occurs in 3-5% of young adults; extensive seborrhoeic dermatitis may occur in early HIV infection. The yeast Pityrosporum ovale is increased in the scaly epidermis in this condition and is now implicated in its pathogenesis, although the mechanism is not entirely clear.
In irritant dermatitis the rash is caused by physical or chemical irritation and damage of the skin; allergy is not usually implicated. Soaps, detergents, foods and DIY materials can all produce this pattern. Hand dermatitis is the most common
form (2.37). Asteatotic dermatitis is common in elderly and hospitalized patients.
The principles of management in dermatitis are similar, whether the diagnosis is atopic eczema or contact dermatitis (2.38). Allergen or irritant avoidance is particularly important in contact dermatitis and if there is hand involvement.
Most eczema responds best to topical corticosteroids, but it is important to avoid the local (2.39, 2.91) and systemic side effects associated with excessive steroid use. In general, topical steroids should be used intensively for short periods, and chronic use should be avoided whenever possible. Occlusive dressings may help to achieve the maximum short-term benefit from topical corticosteroid use.
In the long term, patients with dermatitis of any cause should avoid soap and use lubricants liberally. Other therapy as outlined in 2.38 is indicated in selected patients.
 

2.23 Lichenified eczema results from repeated scratching of lesions in eczematous patients.

2.24 Infantile eczema in a dark-skinned child, affecting the face, neck and trunk. In a lightskinned child, the lesions are pinkish rather than bluish in colour.

2.25 Flexural atopic dermatitis. This girl shows the typical childhood distribution. As the lesions are itchy, they are usually scratched repeatedly and become excoriated. In the long term, lichenification results (see 2.23). Even nonflexural skin is dry and may be itchy.

2.26 Secondary infection in eczema. Patients with atopic dermatitis have defective cell-mediated immunity, and are more susceptible to bacterial, viral and fungal infections. This man has a herpes simplex infection (eczema herpeticum), which has prevented him from shaving (see p. 26).

2.27 Neurodermatitis, or lichen simplex chronicus, usually presents with a single, flexed, lichenified plaque, which is perpetuated by repeated rubbing or scratching, either as a habit or as a response to stress. In this Asian patient, the end result was post-inflammatory hypopigmentation.

2.28 Chronic nodular prurigo. This condition usually  affects middle-aged and elderly women who present with pruritic nodules on the legs and arms. A few cases may have an underlying iron deficiency, but the majority area form ou neurodermatitis.

2.29 Discoid dermatitis. Round plaques of eczema develop, usually on the extensor surfaces of the limbs. The condition often occurs in patients who have no previous history of atopic dermatitis. In this patient the lesions are 'weeping' serous fluid.

2.30 Pompholyx, or pustular eczema, of the hand.   form of atopic eczema may be proved by external factors, This including a fungal infection elsewhere on the skin (an'id reaction') or possibly the ingestion of small amounts of nickel by a patient with contact sensitivity to the metal. Secondary infection of the vesicles is common, and both often required.

2.31 Contact dermatitis to poison ivy is a common problem in North America. This 15-year-old boy presented with linear eczematous lesions on his ankle.

2.32 Contact dermatitis to nickel affects 10% of European women. Nickel is a common component of jewellery such as rings, necklaces and earrings. Nickel in earrings gave rise to earlobe eczema in this young woman.

2.33 Stasis eczema is commonly seen in elderly women, in association with venous insufficiency or frank ulceration. Often, as here, there is also marked pigmentation as a result of haemosiderin deposition.

2.34 Contact blepharitis. Characterized by redness and swelling of the eyelid margins, this can result from contact dermatitis caused by eye make-up, as in this 22-year-old woman.

2.35 Seborrhoeic dermatitis in infancy. Napkin rash is associated with scattered erythematous patches on the abdomen, trunk and head and neck, but the extremities are spared.

2.36 Florid seborrhoeic dermatitis in close-up, showing typical red, scaly lesions. This patient was HIV positive (see p. 12); however although this is a common problem in HIV-infected patients, most patients with seborrhoeic dermatitis do not have HIV infection.

2.37 Irritant dermatitis on the hands of a 39year-old man. It resulted from exposure to irritant chemicals at work.

2.38 The management of eczema/dermatitis. The principles of management are similar, whatever the cause.

2.39 Topical steroidinduced striae on the thigh of a patient with atopic eczema. These were caused by overuse of potent steroid therapy. It is essential to avoid the inappropriate and/or excessive use of steroids in such treatment for all dermatological conditions. Additional complications of excessive corticosteroid therapy include other skin changes as seen in Cushing's syndrome (7.27-7.29), delayed healing of wounds, masking of fungal and bacterial infections, and exacerbation of pustular acne.

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