Subcorneal pustules: Candida, acropustulosis of infancy, transient neonatal pustular melanosis, Sneddon–Wilkinson (and IgA pemphigus), impetigo, pustular psoriasis, Staphylococcus scalded-skin syndrome (CAT SIPS, or an anagram of SIPS)

Guttate psoriasis

Key features

• Neutrophils above parakeratosis

The key histologic feature of guttate psoriasis is a focus of neutrophils on top of parakeratosis (half of the sandwich sign, jelly up). The neutrophilic focus may be small and only visible in step sections. The focus often has a hump-like configuration or resembles a child’s drawing of a seagull.

Fig 8-3 Guttate psoriasis

Inflammatory linear verrucous epidermal nevus (ILVEN)

Key features

• Alternating ortho- and parakeratosis from left to right

• Areas of orthokeratosis have a prominent granular layer

• Areas of parakeratosis lack an underlying granular layer (see Chapter 2)

Fig 8-4 Inflammatory linear verrucous epidermal nevus (ILVEN)

Mycosis fungoides

Fig 8-5 Psoriasiform mycosis fungoides

Syphilis

Fig 8-6 Syphilis

Pearl

Plasma cells are commonly associated with:

• Squamous cell carcinoma

Body locations that recruit plasma cells:

Nutritional-deficiency dermatitis

Key features

• Pallor and ballooning of upper epidermis

Causes include glucagonoma (necrolytic migratory erythema), pellagra, and acrodermatitis enteropathica. Although pallor and ballooning of the upper epidermis are characteristic, many biopsies demonstrate only non-specific dermatitis with diffuse parakeratosis.

Fig 8-7 Necrolytic migratory erythema

Granular parakeratosis

Key features

• Compact hyperkeratosis with parakeratosis

• Granules in stratum corneum

• Granular layer preserved

Fig 8-8 Granular parakeratosis

Porokeratosis

Key features

• Cornoid lamella (column of parakeratosis at 45° angle, dyskeratotic cells below)

• Zone between cornoid lamellae may appear lichenoid or psoriasiform (see Chapter 7)

Fig 8-9 Porokeratosis

Acute spongiotic dermatitis

Key features

• Spongiosis (intercellular edema)

• Exocytosis of lymphocytes

Fig 8-10 Acute spongiotic dermatitis

Seborrheic dermatitis

Key features

• Psoriasiform spongiotic dermatitis

• Neutrophilic scale/crust at edges of follicular ostium

Subacute spongiotic dermatitis

Key features

• Parakeratosis

• Acanthosis

• Spongiosis (intercellular edema)

• Exocytosis of lymphocytes

Fig 8-11 Subacute spongiotic dermatitis

Common causes of spongiotic dermatitis

• Allergic contact dermatitis

• Dyshidrotic dermatitis

• Nummular dermatitis

• Stasis dermatitis

• Id reaction

• Pityriasis rosea

• Spongiotic pigmenting purpura

• Tinea

Chronic dermatitis (lichen simplex chronicus)

Key features

• Compact stratum corneum

• Stratum lucidum as in volar skin, but follicles are present (hairy palm appearance)

• Irregular acanthosis

• Papillary dermal fibrosis

The histologic findings of chronic dermatitis are those of lichen simplex chronicus. Excoriation commonly produces focal superficial epidermal necrosis. Papillary dermal fibrosis is commonly accompanied by capillary proliferation (angiofibroplasia). Vertical streaking of papillary dermal collagen is common.

Fig 8-12 Lichen simplex chronicus

Pityriasis rosea

Key features

• Subacute spongiotic dermatitis

• Erythrocyte extravasation

• Transepidermal elimination of erythrocytes

The herald patch of pityriasis rosea is broad and fairly uniform in appearance. The subsequent lesions demonstrate a migrating spongiotic focus, followed by a trailing scale. The focus and scale form a roughly 45° angle.

Fig 8-13 Pityriasis rosea (RBC, red blood cell)

Spongiotic pigmented purpuric eruption (PPE)

Key features

• Spongiosis

• Inflammation purely lymphoid

• Surrounds capillaries (centered above the level of the post-capillary venule)

• Erythrocyte extravasation

• Hemosiderin deposits over time

Fig 8-14 Pigmented purpuric eruption (RBC, red blood cell)

Stasis dermatitis

Key features

• Subacute spongiotic dermatitis

• Cannonball-like angioplasia in the superficial dermis

• Hemosiderin

Pearl

Hemosiderin is refractile, whereas melanin is not.

Fig 8-15 Stasis dermatitis

Spongiotic dermatitis with intraepidermal eosinophils

Key features

• Spongiosis

• Eosinophils within the epidermis (“eosinophilic spongiosis”)

Pearl

Causes include herpes gestationis, arthropod bite, allergic contact dermatitis, pemphigus, pemphigoid, incontinentia pigmenti, erythema toxicum (spongiosis adjacent to a follicle) (HAAPPIE).