White : Diseases of the Skin - Approach to the Patient

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Gary M. White & Neil H. Cox

Diseases of the Skin

2	Approach to the Patient

REGIONAL DERMATOLOGY AND SITES OF PREDILECTION

Some disorders have a suffciently strong predilection for specific body sites that this can be diagnostically useful. In some instances, it is useful to have a list of likely diagnoses when a lesion or eruption is localized to one specific site (Tables 2.3and2.4,Figs 2.30 and2.31). Most disorders listed are discussed in other chapters, but a specific list of flexural rashes and lesions has been provided in Table 2.4, as rashes at these sites often create diagnostic difficulty (see also Fig. 2.32).

Figure. 2.30 Photosensitivity affects exposed areas of skin, typically the face, V of the neck, and exposed parts of the arms. Note the sparing of the area under a watch strap.

Table 2.3 SOME DISORDERS THAT HAVE PREDILECTION FOR SPECIFIC BODY SITES

Body site	Disorders
Scalp	Hair disorders and alopecia, psoriasis, seborrheic dermatitis, lichen simplex (nape of neck), pilar cysts, organoid nevus (a hamartoma), cutaneous metastases of internal malignancy
Eyelids	Atopic dermatitis, contact allergy (cosmetics, nickel), seborrheic blepharitis, angioedema, dermatomyositis, basal cell carcinoma, xanthelasma
Face	Acne, atopic dermatitis, seborrheic dermatitis (especially eyebrows and nasolabial crease), causes of butterfly rash (rosacea, erysipelas, lupus erythematosus, lupus pernio, erythema infectiosum), photosensitivity, nevi and freckles, actinic keratoses, basal and squamous cell carcinomas, keratoacanthoma, lentigo maligna
Lips	Dermatitis (atopic, contact), cheilitis (angular, actinic), angioedema, contact urticaria, impetigo, erythema multiforme, warts, vascular lesions (venous lake, pyogenic granuloma), squamous cell carcinoma
Hands	Dermatitis (dyshidrotic, pompholyx, contact), psoriasis and palmoplantar pustulosis, keratodermas, dermatophyte infections, erythema multiforme, photosensitivity (dorsal hand), scabies (especially finger webs), collagen vascular disorders and vasculitis (especially nail fold and fingertip), viral warts, actinic keratoses, squamous cell carcinoma, granuloma annulare, nail disorders
Limbs	Psoriasis (elbows, knees), atopic dermatitis (limb flexures), discoid eczema, venous eczema and ulceration (lower leg), asteatotic eczema (lower leg), lichen simplex (lower leg), lichen planus (flexor forearms, shins), dermatitis herpetiformis (knee, elbow), granuloma annulare (elbows), erythema nodosum (legs), vasculitis (legs), papular urticaria or flea bites (lower leg), dermatofibroma, Bowen disease (lower leg)
Feet	Dermatitis (pompholyx, contact, juvenile plantar), psoriasis and palmoplantar pustulosis, dermatophyte fungal infection (skin and nails), pitted keratolysis, vasculitis and arterial disease, callosities or corns, verrucae
Axillae	See Table 2.4
Genital	Psoriasis or Reiter syndrome, lichen planus (penis), lichen sclerosus (penis, vulva), lichen simplex (scrotum, vulva), fixed drug eruption (penis), sexually transmitted diseases or genital warts, Zoon balanitis (glans penis), epidermoid cysts (scrotal), squamous cell carcinoma (penis, vulva)

Figure. 2.31 Dermatitis herpetiformis: rather minor-looking lesions, but with intense itch and with a characteristic distribution pattern including scalp, scapulae, sacrum, elbows, and knees (but beware—scabies may mimic this pattern and morphology of lesions, although it usually affects the hands as well).

In other cases, a particular combination of affected sites is characteristic.
Some examples are as follows.

•	Psoriasis–elbows, knees, scalp, low back, and nails (Ch. 7).
•	Scabies–hands, wrists, elbows, waistline, genitalia (male), and periareolar (women) (Ch. 27).
•	Photosensitivity–face, V of neck, dorsal hands and forearms, sparing under watch strap (Fig. 2.30 and Ch. 17).
•	Atopic dermatitis–antecubital and popliteal fossae, wrists, and ankles (varies with age group; Ch. 6).
•	Dermatitis herpetiformis–elbows, knees, scapulae, sacrum, and scalp (Fig. 2.31).

Figure. 2.32 Granular parakeratosis. This flexural disorder most commonly affects axillae, and may suggest commoner diagnoses such as contact dermatitis or (because of the site and the crusting) Hailey–Hailey disease. (Courtesy of Dr. G. Dawn.)

Certain features should prompt careful examination of distant sites, particularly in situations where the patient may not volunteer information. A few examples are as follows.

•	Lichen planus. Any purple or violaceous papular rash should arouse suspicion of lichen planus. About 75% of patients have oral involvement (see Ch.8), but this is asymptomatic in 75% of these individuals, therefore the mouth must be examined at the instigation of the doctor.
•	Scabies. Genital and breast involvement is common but may not be volunteered due to embarrassment. Specific examination of these sites may be of diagnostic importance.
•	Psoriasis. Nail involvement is common, especially if psoriasis affects the hands. The nail changes may be clinically diagnostic even though the skin lesions may be non-specific in some patients.
•	Lupus erythematosus. A butterfly rash on the face can cause great anxiety for doctors, but may be due to rosacea or seborrheic dermatitis rather than to lupus erythematosus. Nail fold telangiectasia is a useful feature to confirm a connective tissue disorder but is usually asymptomatic (Fig. 2.33).

Table 2.4 SOME DISORDERS THAT HAVE PREDILECTION FOR FLEXURAL SITES

Type of disorder	Disorder	Comments ^a
Inflammatory dermatoses	Psoriasis Seborrheic dermatitis Contact dermatitis Intertrigo Napkin rash Lichen planus Hidradenitis suppurativa Crohn disease Atopic dermatitis	Common in flexures, typically red and shiny rather than the usual white scale (Ch. 7); termed the inverse pattern if mainly flexural distribution Usually with lesions elsewhere also (Ch. 6) Irritant or allergic; may affect the vault of the axilla (e.g. deodorants) or axillary folds (e.g. clothing dermatitis) (Ch. 6) Especially inframammary; may be due to simple maceration, but also secondary infection may occur (staphylococcal, streptococcal, candidal) Many causes; the commonest are irritant and candidal (see Ch.19) Not often mainly flexural but may cause confusion, as flexural and genital lesions are often brown infection may occur (staphylococcal, streptococcal, candidal)or annular, rather than the usual purplish plaques Affects axillae, groin, inframammary area (Ch.10) Cutaneous lesions affect especially the perineum (Ch.12) Affects elbow and knee flexures, uncommonly the major flexures, other than in infants, when the process may be generalized
Bullous diseases	Pemphigus vegetans Hailey–Hailey disease	Rare, mainly flexural (Ch.16) Inherited, variable (see Ch.19)
Infections	Dermatophytes Erythrasma Trichomycosis axillaris Candidiasis Bacterial Scabies	Especially male groin—always look for evidence of associated tinea pedis (Ch. 26) Brownish color, fluoresces under Wood's light ( Ch. 24) Coated hair shafts (see Ch. 24) Especially in napkin rash or in bed-bound elderly adults, commoner in diabetes; satellite pustules are characteristic Various types: follicular infections (furuncles), perianal abscesses, secondary infection of intertrigo,gram-negative toe web infections, etc. gram-negative toe web infections, etc. Multiple itchy flexural nodules are highly suggestive of the relatively chronic nodular variant; penile lesions are also common in this pattern (Ch. 27)
Localized lesions	Fibroepithelial polyps (skin tags) Neurofibromatosis Fox–Fordyce disease Pseudoxanthoma elasticum	Common normal variant Axillary freckling is seen (Crowe sign) An apocrine occlusion dermatosis (see Ch. 23) Inherited defect of elastic tissue, most apparent on the neck and axillae (Ch. 22)
Miscellaneous	Hyperhidrosis and other sweat apparatus disorders Acanthosis nigricans Acrodermatitis enteropathica or zinc deficiency Langerhans cell histiocytosis Granular parakeratosis	Mainly axillae (see Ch. 23) May be endocrine-related or paraneoplastic (see Ch. 12) Severe napkin rash and perioral rash in an infant (Ch.19), acquired version in adults; migratory erythema of glucagonoma syndrome may have the same pattern May present as severe napkin rash ( Ch.19) Rare; hyperkeratotic, mainly adult female axilla (Fig. 2.32)

^aAll refer to major flexures unless specified.

Non-cutaneous sites

The hair and nails are modified skin structures and may be abnormal in numerous dermatoses. The teeth are also ectodermal structures that may be involved in a variety of inherited disorders. Examination of the mouth and other mucosal surfaces (conjunctivae, genital) may yield useful information as part of the examination of the skin (Ch. 20).

Figure. 2.33 Dermatomyositis. ( a ) Streaky rash on the dorsum of the fingers.
( b ) This is a condition where examination of the nail folds is specifically useful; illustrated are the characteristic connective tissue changes of an elongated ragged cuticle and prominent capillary loops within a sclerotic dermis.