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Psoriasis

Pityriasis Rubra Pilaris

Epidermal acanthosis

Regular

Regular mild

Parakeratosis

Confluent

Alternating ortho and parakeratosis

Suprapapillary epidermal plates

Thin

Normal to thick

Follicular hyperkeratotoic plugs

No

Yes

Neutrophils in epidermis

Yes

■ Uncertain but keratinocyte dysfunction and vitamin A may play a role

References:

1. Magro CM, Crowson AN. The clinical and histomorphological features of pityriasis rubra pilaris. A comparative analysis with psoriasis. J Cutan Pathol 1997; 24(7):416-424.

2. Allison DS, El-Azhary RA, Calobrisi SD, Dicken CH. Pityriasis rubra pilaris in children. J Am Acad Dermatol 2002; 47(3): 386-389.

INFLAMMATORY LINEAR VERRUCOUS EPIDERMAL NEVUS Clinical Presentation:

■ Linear to curved, whorled (Blaschkoid) verrucous scaly plaques

■ Lower extremity

■ Occurs more frequently in children than in adults

■ Can look identical to lichen striatus, but is persistent

Histology:

■ Psoriasiform epidermal hyperplasia

■ Compact orthkeratotic hyperkeratosis alternating with parakeratosis

■ Polymorphonuclear leukocytes in epidermis are rarely seen

■ Mild spongiosis

Histologic Differential Diagnosis:

See Tables 2A and B.

Table 3 Histologic Differential Diagnosis: Spongiotic Dermatoses

Pattern

Acute

Subacute

Chronic

Stratum corneum

Orthokeratotic

Parakeratosis and orthokeratosis

Hyperkeratotic orthokeratosis, or parakeratosis

Epidermal acanthosis

None to minimal

Mild to moderate

Moderate to marked

Spongiosis

Mild to marked, usually marked

Mild to moderate

Minimal to absent

Intraepidermal vesicles

Yes

Rare

No

Dermal perivascular inflammation

Eosinophils and lymphocytes

Lymphocytes and sometimes eosinophils

Lymphocytes and rare eosinophils

Dermal fibrosis

No

No

Yes

Clinical prototype

Allergic contact dermatitis

Nummular dermatitis

Lichen simplex chronicus

Pathophysiology:

■ Altered keratinocyte differentiation

Reference:

1. Lee SH, Rogers M. Inflammatory linear verrucous epidermal naevi: a review of 23 cases. Australas J Dermatol 2001; 42(4): 252-256.

This group of disorders is characterized by the histologic finding of spongiosis. Clinical pathologic correlation is essential as several disease entities may appear indistinguishable histologically and yet be clinically distinct. Many of these disorders present with vesicles or bullae in their early or acute forms. Epidermal spongiosis is one mechanism by which intraepidermal vesicles are formed.

In general, the spongiotic dermatoses can be divided histologically into a spectrum of acute, subacute, and chronic forms (Table 3).

Clinicopathologic Correlation:

Acute spongiotic pattern is commonly seen in these clinical entities

■ Allergic contact dermatitis

■ Irritant contact dermatitis

■ Dyshidrotic dermatitis

■ Photoallergic dermatitis

■ Incontinentia pigmenti (stage I)

■ Bullous dermatophyte

ALLERGIC CONTACT DERMATITIS Clinical Presentation:

■ Pruritic, erythematous, edematous papules, and plaques

■ Linear lesions or pattern of contact

■ Toxicodendron species (poison ivy, oak, sumac) common culprits

Histology:

■ Acute spongiotic pattern (Fig. 7)

■ Marked spongiosis with intraepidermal spongiotic vesicles

■ Orthokeratosis

■ Eosinophils and lymphocytes—within the dermis and sometimes in the epidermis

■ Collections of Langerhan cells in epidermis

Histologic Differential Diagnosis:

See Table 4.

Subacute spongiotic pattern is commonly seen in these clinical entities:

■ Nummular dermatitis

■ Pityriasis rosea

■ Seborrheic dermatitis

■ Fungal/dermatophyte infection

■ Figurate erythema/erythema annulare centrifugum

■ Pruritic dermatoses of pregnancy

■ Gianotti-Crosti syndrome/papular acrodermatitis of childhood

■ Polymorphous light eruption; "spongiotic" variant

NUMMULAR DERMATITIS Clinical Presentation:

■ Pruritic round to oval "coin" shaped pink plaques (Fig. 8)

■ May be vesicular, but more often with scale and crust

■ Lower extremities commonly involved in men

■ Mild to moderate epidermal acanthosis

■ Mild to moderate spongiosis

■ Usually no spongiotic vesicles

■ Focal parakeratotic stratum corneum

■ Superficial perivascular lymphocytes, sometimes eosinophils

■ Surface scale crust

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