An overview of dermatologic diagnosis and procedures

Configuration of lesions

A number of dermatologic entities assume annular, circinate, or ring shapes and are interpreted as ringworm or superficial fungal infections. Although tinea is a common annular dermatosis of childhood, there are multiple other disorders that must be included in the differential diagnosis of ringed lesions, including pityriasis rosea, seborrheic dermatitis, nummular eczema, lupus erythematosus, granuloma annulare, annular psoriasis, erythema multiforme, erythema annulare centrifugum, erythema migrans, secondary syphilis, sarcoidosis, urticaria, pityriasis alba, tinea versicolor, lupus vulgaris, drug eruptions, and cutaneous T-cell lymphoma.

The terms arciform and arcuate refer to lesions that assume arc-like configurations. Arciform lesions may be seen in erythema multiforme, urticaria, pityriasis rosea, bullous dermatosis of childhood, and sometimes epidermolysis bullosa simplex.

Lesions that tend to merge are said to be confluent . Confluence of lesions is seen, for example, in childhood exanthems, Rhus dermatitis, erythema multiforme, tinea versicolor, and urticaria.

Lesions localized to a dermatome supplied by one or more dorsal ganglia are referred to as dermatomal . Herpes zoster classically occurs in a dermatomal distribution.

Discoid is used to describe lesions that are solid, moderately raised, and disc shaped. The term has largely been applied to discoid lupus erythematosus, in which the discoid lesions usually show atrophy and dyspigmentation.

Discrete lesions are individual lesions that tend to remain separated and distinct. Eczematoid and eczematous are adjectives relating to inflamed, dry skin with a tendency to thickening, oozing, vesiculation, and/or crusting; although atopic dermatitis is a classic eczematous disorder, other examples of eczema are contact, nummular, and dyshidrotic forms.

Grouping and clustering are characteristic of vesicles of herpes simplex or herpes zoster, insect bites, lymphangioma circumscriptum, contact dermatitis, and bullous dermatosis of childhood.

Guttate or drop-like lesions are characteristic of flares of psoriasis in children and adolescents that follow an acute upper respiratory tract infection, usually streptococcal.

Gyrate refers to twisted, coiled, or spiral-like lesions, as may be seen in patients with urticaria and erythema annulare centrifugum.

Iris or target-like lesions are concentric ringed lesions characteristic of erythema multiforme. The classic “targets” in this condition are composed of a central dusky erythematous papule or vesicle, a peripheral ring of pallor, and then an outer bright red ring.

Keratosis refers to circumscribed patches of horny thickening, as seen in seborrheic or actinic keratoses, keratosis pilaris, and keratosis follicularis (Darier disease). Keratotic is an adjective pertaining to keratosis and commonly refers to the epidermal thickening seen in chronic dermatitis and callus formation.

The Koebner phenomenon or isomorphic response refers to the appearance of lesions along a site of injury. The linear lesions of warts and molluscum contagiosum, for example, occur from autoinoculation of virus from scratching; those of Rhus dermatitis (poison ivy) result from the spread of the plant’s oleoresin. Other examples of disorders that show a Koebner phenomenon are psoriasis, lichen planus, lichen nitidus, pityriasis rubra pilaris, and keratosis follicularis (Darier disease).

Lesions in a linear or band-like configuration appear in the form of a line or stripe and may be seen in epidermal nevi, Conradi syndrome, linear morphea, lichen striatus, striae, Rhus dermatitis, deep mycoses (sporotrichosis or coccidioidomycosis), incontinentia pigmenti, pigment mosaicism, porokeratosis of Mibelli, or factitial dermatitis. In certain genetic and inflammatory disorders, such linear configurations represent the lines of Blaschko, which trace clones of embryonic epidermal cells and, as such, represent a form of cutaneous mosaicism. This configuration presents as a linear pattern on the extremities, wavy or S -shaped on the lateral trunk, V -shaped on the central trunk, and varied patterns on the face and scalp.

Moniliform refers to a banded or necklace-like appearance. This is seen in monilethrix, a hair deformity characterized by beaded nodularities along the hair shaft.

Multiform refers to disorders in which more than one variety or shape of cutaneous lesions occurs. This configuration is seen in patients with erythema multiforme, urticaria multiforme, early Henoch–Schönlein purpura, and polymorphous light eruption.

Nummular means coin shaped and is usually used to describe nummular dermatitis.

Polycyclic refers to oval lesions containing more than one ring, as commonly is seen in patients with urticaria.

A reticulated or net-like pattern may be seen in erythema ab igne, livedo reticularis, cutis marmorata, cutis marmorata telangiectatica congenita, and lesions of confluent and reticulated papillomatosis.

Serpiginous describes the shape or spread of lesions in a serpentine or snake-like configuration, particularly those of cutaneous larva migrans (creeping eruption) and elastosis perforans serpiginosa.

Umbilicated lesions are centrally depressed or shaped like an umbilicus or navel. Examples include lesions of molluscum contagiosum, varicella, vaccinia, variola, herpes zoster, and Kaposi varicelliform eruption.

Universal (universalis) implies widespread disorders affecting the entire skin, as in alopecia universalis.

Zosteriform describes a linear arrangement along a nerve, as typified by lesions of herpes zoster, although herpes simplex infection can also manifest in a zosteriform distribution.

Distribution and morphologic patterns of common skin disorders

The regional distribution and morphologic configuration of cutaneous lesions are often helpful in dermatologic diagnosis.

Acneiform lesions are those having the form of acne, and an acneiform distribution refers to lesions primarily seen on the face, neck, chest, upper arms, shoulders, and back (see Fig. 8.3, Fig. 8.4, Fig. 8.5, Fig. 8.6, Fig. 8.7, Fig. 8.8 ).

Sites of predilection of atopic dermatitis include the face, trunk, and extremities in young children; the antecubital and popliteal fossae are the most common sites in older children and adolescents (see Fig. 3.1, Fig. 3.2, Fig. 3.3, Fig. 3.4, Fig. 3.5, Fig. 3.6, Fig. 3.7, Fig. 3.8, Fig. 3.9, Fig. 3.10, Fig. 3.11 ).

The lesions of erythema multiforme may be widespread but have a distinct predilection for the hands and feet (particularly the palms and soles) (see Fig. 20.35, Fig. 20.36, Fig. 20.37 ).

Lesions of herpes simplex may appear anywhere on the body but have a distinct predisposition for the areas about the lips, face, and genitalia (see Fig. 15.1, Fig. 15.2, Fig. 15.3, Fig. 15.4 ). Herpes zoster generally has a dermatomal or nerve-like distribution and is usually but not necessarily unilateral (see Fig. 15.15, Fig. 15.16, Fig. 15.17 ). More than 75% of cases occur between the second thoracic and second lumbar vertebrae. The fifth cranial nerve commonly is involved, and only rarely are lesions seen below the elbows or knees.

Lichen planus often affects the limbs (see Figs. 4.54 , 4.55 , and 4.58 ). Favorite sites include the lower extremities, the flexor surface of the wrists, the buccal mucosa, the trunk, and the genitalia.

The lesions of lupus erythematosus most commonly localize to the bridge of the nose, malar eminences, scalp, and ears, although they may be widespread (see Figs. 22.3 and 22.4 ). Patches tend to spread at the border and clear in the center with atrophy, scarring, dyspigmentation, and telangiectases. The malar or butterfly rash is neither specific for nor the most common sign of lupus erythematosus; telangiectasia without the accompanying features of erythema, scaling, or atrophy is never a marker of this disorder other than in neonatal lupus.

Molluscum contagiosum is a common viral disorder characterized by dome-shaped, skin-colored to erythematous papules, often with a central white core or umbilication (see Fig. 15.41, Fig. 15.42, Fig. 15.43, Fig. 15.44, Fig. 15.45, Fig. 15.46, Fig. 15.47 ). These papules most often localize to the trunk and axillary areas. Although molluscum lesions can be found anywhere, the scalp, palms, and soles are rare sites of involvement.

Photodermatoses are cutaneous disorders caused or precipitated by exposure to light. Areas of predilection include the face, ears, anterior V of the neck and upper chest, dorsal aspect of the forearms and hands, and exposed areas of the legs. The shaded regions of the upper eyelids, subnasal, and submental regions tend to be spared. The major photosensitivity disorders are lupus erythematosus, dermatomyositis, polymorphous light eruption, drug photosensitization, phototoxic reactions, and porphyria (see Chapter 19 ).

Photosensitive reactions cannot be distinguished on a clinical basis from lesions of photocontact allergic conditions. They may reflect internal as well as external photoallergens and may simulate contact dermatitis from airborne sensitizers. Lupus erythematosus can be differentiated by the presence of atrophy, scarring, hyperpigmentation or hypopigmentation, and periungual telangiectases. Dermatomyositis with swelling and erythema of the cheeks and eyelids should be differentiated from allergic contact dermatitis by the heliotrope hue and other associated changes, particularly those of the fingers (periungual telangiectases and Gottron papules).

Pityriasis rosea begins as a solitary round or oval scaling lesion known as the herald patch in 70% to 80% of cases, which may be annular and is often misdiagnosed as tinea corporis (see Fig. 4.49 ). After an interval of days to 2 weeks, affected individuals develop a generalized symmetric eruption that involves mainly the trunk and proximal limbs. The clue to diagnosis is the distribution of lesions, with the long axis of these oval lesions parallel to the lines of cleavage in what has been termed a Christmas-tree pattern (see Figs. 4.50 , 4.51 , and 4.53 ). A common variant, inverse pityriasis rosea, often localizes in the inguinal region (see Fig. 4.52 ), but the parallel nature of the long axis of lesions remains characteristic.

Psoriasis classically consists of round, erythematous, well-marginated plaques with a rich red hue covered by a characteristic grayish or silvery-white mica-like (micaceous) scale that on removal may result in pinpoint bleeding (Auspitz sign) (see Fig. 4.1, Fig. 4.2, Fig. 4.3, Fig. 4.4, Fig. 4.5, Fig. 4.6, Fig. 4.7, Fig. 4.8, Fig. 4.9, Fig. 4.10, Fig. 4.11, Fig. 4.12, Fig. 4.13, Fig. 4.14, Fig. 4.15, Fig. 4.16 ). Although exceptions occur, lesions generally are seen in a bilaterally symmetric pattern with a predilection for the elbows, knees, scalp, and lumbosacral, perianal, and genital regions. Nail involvement, a valuable diagnostic sign, is characterized by pitting of the nail plate, discoloration, separation of the nail from the nailbed (onycholysis), and an accumulation of subungual scale (subungual hyperkeratosis). A characteristic feature of this disorder is the Koebner or isomorphic response in which new lesions appear at sites of local injury.

Scabies is an itchy disorder in which lesions are characteristically distributed on the wrists and hands (particularly the interdigital webs), forearms, genitalia, areolae, and buttocks in older children and adolescents (see Fig. 18.1, Fig. 18.2, Fig. 18.3, Fig. 18.4, Fig. 18.5, Fig. 18.6, Fig. 18.7, Fig. 18.8, Fig. 18.9, Fig. 18.10, Fig. 18.11, Fig. 18.12 ). Other family members may be similarly affected or complain of itching. In infants and young children, the diagnosis is often overlooked because the distribution typically involves the palms, soles, and often the head and neck. Obliteration of demonstrable primary lesions (burrows) because of vigorous hygienic measures, excoriation, crusting, eczematization, and secondary infection is particularly common in infants.

Seborrheic dermatitis is an erythematous, scaly or crusting eruption that characteristically occurs on the scalp, face, and postauricular, presternal, and intertriginous areas (see Figs. 3.3 , 3.44 , and 3.45 ). The classic lesions are dull, pinkish-yellow, or salmon colored with fairly sharp borders and overlying yellowish greasy scale. Morphologic and topographic variants occur in many combinations and with varying degrees of severity from mild involvement of the scalp with occasional blepharitis to generalized, occasionally severe erythematous scaling eruptions. The differential diagnosis may include atopic dermatitis, psoriasis, various forms of diaper dermatitis, Langerhans cell histiocytosis, scabies, tinea corporis or capitis, pityriasis alba, contact dermatitis, Darier disease, and lupus erythematosus.

Warts are common viral cutaneous lesions characterized by the appearance of skin-colored small papules of several morphologic types (see Fig. 15.19, Fig. 15.20, Fig. 15.21, Fig. 15.22, Fig. 15.23, Fig. 15.24, Fig. 15.25, Fig. 15.26, Fig. 15.27, Fig. 15.28, Fig. 15.29, Fig. 15.30, Fig. 15.31, Fig. 15.32, Fig. 15.33, Fig. 15.34, Fig. 15.35, Fig. 15.36, Fig. 15.37 ). They may be elevated or flat lesions and tend to appear in areas of trauma, particularly the dorsal surface of the face, hands, periungual areas, elbows, knees, feet, and genital or perianal areas. Close examination may reveal capillaries appearing as punctate dots scattered on the surface.