Distribution of eruption or lesions

Stand back from the patient and observe the pattern of the eruption (Fig. 1). Determine whether it is localized (e.g. a tumour) or widespread (e.g. a rash). If the latter, determine whether the eruption is symmetrical and, if so, peripheral or central. Note whether it involves the flexures (e.g. atopic eczema) or the extensor aspects (e.g. psoriasis). Is it limited to sun-exposed areas? Is it linear?

Dermatomal patterns are also seen. Herpes zoster (shingles) is the commonest example of this, but some naevi also appear in this guise or follow Blaschko’s lines (p. 13). Regional patterns (see Fig. 1), e.g. involvement of the groin or axilla, will suggest certain diagnoses to the experienced physician. For example, guttate psoriasis and tinea versicolor tend to occur on the trunk, whereas lichen planus often occurs around the wrists, and contact dermatitis frequently affects the face, feet or hands. The factors resulting in these patterns are complex but include skin anatomy, e.g. blood vessels, nerves, appendages or embryonic lines, and environment, e.g. moist conditions in the axillae, chemical contacts and sun exposure.

Morphology of individual lesions

A hand lens or dermoscope is often helpful in looking at individual lesions. Palpation (often neglected by medical students) is also important to determine the consistency, depth and texture. Definitions of lesions are given on page 14.

Lesions may be monomorphic (e.g. guttate psoriasis) or pleomorphic (e.g. chickenpox). There may also be secondary changes on top of primary lesions. The local configuration of lesions is often of diagnostic help (Table 1). Determine whether the lesions are grouped, linear or annular, or if they show the Koebner phenomenon (p. 28), whereby lesions appear in an area of trauma which is often linear, e.g. a scratch.

Table 1 Configuration of lesions

Case history 1

An 8-year-old girl gave a 12-month history of an itchy eruption affecting the antecubital and popliteal fossae (Fig. 2). Her mother had had a similar rash as a child. The pattern and the morphology were characteristic.

Fig. 2 Atopic eczema affecting the popliteal fossae.

Diagnosis: atopic eczema (p. 36).

Nails, hair and mucous membranes

The nails, scalp and hair frequently show diagnostic and even pathognomonic signs (p. 68). With any unusual or atypical eruption, the mucous membranes of the mouth and genitalia may show important changes, such as oral involvement by Wickham’s striae in lichen planus, oral lesions in Kaposi’s sarcoma or vulval involvement with lichen sclerosus.

General examination

Palpation of lymph nodes is important in patients with skin malignancy. In patients with a skin lymphoma, a full examination is needed, looking particularly for lymphadenopathy and hepatosplenomegaly. Palpation of pedal pulses is vital in patients with leg ulcers.

Case history 2

Six weeks ago, a 25-year-old man developed a slightly itchy linear area running down the medial aspect of his left leg (Fig. 3). Dermatological conditions giving a linear eruption include lichen planus, morphoea, psoriasis and linear epidermal naevus.

Fig. 3 Lichen striatus affecting the left leg.

Diagnosis: lichen striatus, a self-limiting inflammatory dermatitis of unknown origin.

Special techniques and assessment of disease morbidity

The diagnoses of many skin conditions can be helped by special techniques, detailed on page 20. Photography is often used to record the state of a patient’s skin disease and allows comparisons at follow-up visits.

In the current management of skin diseases, it is sometimes necessary to make a quantitative evaluation of the disease and its impact on a patient’s life. For example, the National Institute for Health and Clinical Excellence (NICE) states that a patient’s psoriasis must be of a certain severity, according to the psoriasis area and severity index, before treatment with a biologic agent is recommended (p. 115).

Web resource

http://www.youtube.com/watch?v=FgRWHw8vrGc