Common abnormalities

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Distribution. The temptation to examine skin lesions closely should be resisted until the distribution of the rash has been noted at arm's length. This may be the most valuable clue to the diagnosis. For example, it is not easy to diagnose herpes /,osier by the appearance of the individual lesions, but it becomes simple once the dermatomal distribution is appreciated (Fig. 2.19A), Similarly, a photosensitive basis for a rash becomes obvious when it is noted that only exposed areas are involved and shielded areas spared (Fig. 2.19B). Some skin conditions may affect certain areas (sites of predilection) more than others. Psoriasis preferentially involves the scalp, elbows, knees, natal cleft and nails, atopic dermatitis frequently picks out the antecubital and popliteal fossae in children (Fig. 2.I9C) and seboirhoeic dermatitis is seen most often on the scalp, forehead, eyebrows, nasolabial folds and presternal area. The distribution of an eczematous rash may be the main pointer that the problem is due to a reaction from an externa] contactant (Fig. 2.19D).

Universal and symmetrical eruptions favour systemic or constitutional causes, whereas asymmetrical rashes which spread from a single focus are most often due to fungal, bacterial and some viral infections. Frequently, changes on (lie soles of the feet may be mirrored by a similar appearance on the palms. Sometimes clues as to the diagnosis may be found at sites distant to the presenting problem, for example a patient may consult the doctor about a solitary pcntngual fibroma although the diagnosis of tuberous sclerosis becomes evident when ash-leaf depigmented macules on the trunk and adenoma sebaceum on the face

Ash Grey Lesions Tuberous Sclerosis
Fig. 2.18 The effect oi camouflage make-up in a patient with an extensive port wine stain.
Allergic Dermatitis Insect
Fig. 2.19 Distribution of rashes as a key to diagnosis. 0 Herpes zoster. E Griseofulvin photosensitivity eruption. BEI Atopic dermatitis. 0 Allergic dermatitis from contact with rubber gloves.

Morphology. After the distribution has been noted the morphology of the primary lesions should be defined, Unfortunately, scratch marks, crusting and ulceration may obscure the appearance of early lesions though these should be sought and, when found, inspected closely.

Most types of primary lesions have special names (Table 2.9), and these should be used to describe a skin disease properly. The clinician should not only look at the primary lesions carefully but also record details concisely so that the description can be understood and the rash visualised by other's.

With practice, use of the terminology will save much time in describing the rash as well as point to the diagnosis, For example, 'violaceous, shiny, polygonal discrete and flat-topped papules on the fronts of the wrists' are probably due lo lichen planus (Fig. 2.20A), but the diagnosis is clinched by recognition of the pathognomonic Wickham's are noted. In summary, before looking at the detail of the individual lesions, stand back from the patient and consider the following questions.


• Is the rash localised, universal or symmetrical?

• Does the rash follow an anatomical (e.g. ciermatomal) pattern?

• Does it affect special sites such as flexures?

• Are areas of predilection lor some common disease Involved?

• Are certain areas spared?

• Are there other clues lo the diagnosis at sites distant to the presenting problem?

• Are there other incidental findings such as skin cancer which the patient has ignored?

Lichen Planus WristPenis Wheal

Fig. 2.20 Diagnostic seguence, lichen planus. B Discrete flat-topped papules at the wrist, E Wlckham's striae visible on close inspection B White lacy network of striae on buccal mucosa.

TABLE 2.9 Terminology of skin lesions

Primary lesions Papule


Macule Vesicle


Pustule Abscess










Smail solid elevation of skin, less than 0.5 cm in diameter

Elevated area of skin greater than 2 cm in diameter but without substantial depth Small flat area of altered colour or texture Circumscribed elevation of skin, less than 0,5 cm in diameter, and containing fluid Circumscribed elevation of skin over 0.5 cm in diameter and containing fluid A visible accumulation of pus in the skin A localised collection of pus In a cavity, more than 1 cm in diameter

An elevated white compressible, evanescent area produced by dermal oedema A diffuse swelling ol oedema that extends to the subcutaneous tissue A solid mass in the skin, usually greater than 0.5 cm in diameter

A nipple-like mass projecting from the skin Pinhead-sized macules of blood in the skin A larger macule or papule of blood In the skin A larger extravasation ol blood into the skin A swelling from gross bleeding A linear or curvilinear papule, caused by a burrowing scabies mite A plug of keratin and sebum wedged in a dilated pilosebaceous orifice The visible dilatation of small cutaneous blood vessels

Comedo Telangiectasia Secondary lesions [which evolve from primary lesions)


A flake arising from the horny layer


Looks like a scale, but is composed of dried blood or

tissue fluid


An area of skin from which the whole of the epidermis

and at least the upper part of the dermis has been



An ulcer or erosion produced by scratching


An area of skin denuded by a complete or partial loss

of the epidermis


A slit in the skin


A cavity or channel that permits the escape of pus or



The result of healing, in which normal structures are

permanently replaced by fibrous tissue


Thinning of skin due to diminution ol the epidermis,

dermis, subcutaneous fat


A streak-like linear, atrophic, pink, purple or white lesion

of the skin caused by changes in the connective


striae on close inspection of the papules (Fig. 2.20B), and made indisputable by the observation of a while lacy network on the buccal mucosa (Fig. 2.20C); a biopsy for diagnostic purposes in this instance would be like checking the engine specification of a car to determine its make rather than looking at the general shape and (he name on the body!

Most skin lesions are pink; other colours may help in diagnosis, for example the yellow-orange hue of


Fig. 2.20 Diagnostic seguence, lichen planus. B Discrete flat-topped papules at the wrist, E Wlckham's striae visible on close inspection B White lacy network of striae on buccal mucosa.

xanthomata, the violaceous tint of lichen planus, the slaie-grey colour of drug-induced pigmentation (Fig. 2.3A). Variation in colour, asymmetry and an irregular outline are key signs in distinguishing some malignant from benign lesions (Fig. 2.21). The surface characteristics of individual lesions may be equally important diagnostic pointers (Fig. 2.22). Finally, a tiny primary lesion, which might only be


Lentigo Simple
Fig. 2.21 Simple versus malignant lentigo, [a] Simple lesion with well-defined margin. B Malignant lesion with irregular margin and pigmentation.

recognised with the help of a lens, may provide the vital clue in diagnosing a widespread and non-specific rash. The best example of this is the burrow caused by the scabies mile (Fig. 2.23).

Close to the patient, perhaps aided by a lens, the clinician should study individual lesions carefully and ask the following questions.


• What are the characteristics of their margin and surfaces?

Legionella Pneumophila Skin Lesion

Fig. 2.22 Surface characteristics as a key to diagnosis.

H Keratoacanthoma. [II Sasa! ceil carcinoma.

Configuration. Having studied the overall distribution of the rash and the morphology of individual lesions, the clinician should note the arrangement or configuration of the lesion or groups of lesions. Examples in which configuration of lesions aids diagnosis include the Kobner phenomenon in psoriasis and lichen planus, grouping of vesicles in herpes simplex (Fig. 2.24A), the patterning and peripheral spread of urticaria (Fig. 2.24B) and the linear appearance of insect bites (Fig. 2.24C),


• Ultraviolet radiation is the main factor speeding the ageing process in skin.

• Skin lesions often evolve over a period of time. Several examinations during the period of evolution often facilitate diagnosis.

• The overall distribution of a rash may be the most valuable clue to diagnosis.

• The morphology of the primary lesion may be obscured by secondary changes but whenever possible should be carefully defined

Diagram Legionaires Disease

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  • Faruz
    How to analyse individual lesion morphology on the foot?
    7 years ago

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