Histopathology Description - Scaly Plaque Skin Biopsy (H&E, Low-to-Medium Power)

Systematic Description of the Three Images

• Surface shows thick, compact orthokeratosis with overlying scale
• The epidermis is acanthotic - markedly thickened with elongation of the rete ridges
• The rete ridges appear regular and elongated (psoriasiform acanthosis pattern)
• Focal areas of parakeratosis are visible in the stratum corneum (nuclei retained in the horny layer)
• The granular layer appears focally reduced or absent (hypogranulosis) under the parakeratotic areas
• Papillary dermis shows edema and dilated capillary loops
• There is a perivascular lymphocytic infiltrate in the upper dermis
• The dermal collagen is unremarkable in the deeper portions

• The epidermal acanthosis is more prominent, with deep bulbous rete ridge elongation
• The stratum corneum has alternating orthokeratosis and parakeratosis
• Small neutrophilic collections (Munro microabscess-like) appear to be present within the parakeratotic stratum corneum
• The suprapapillary plates are thinned (thinning of the epidermis above dermal papillae)
• The dermal papillae contain dilated, tortuous capillaries
• A superficial perivascular lymphocytic infiltrate is present
• The section edge shows thick overlying scale

• This gives a broader architectural overview
• Confirms psoriasiform epidermal hyperplasia (regular rete ridge elongation)
• The surface shows compact hyperkeratosis with scale
• The dermis beneath shows loose fibrous stroma and dilated vascular spaces
• No obvious deep dermal infiltrate or granuloma formation

Summary of Key Histological Features

Most Likely Diagnosis

Psoriasis Vulgaris (Plaque Psoriasis)

1. Regular psoriasiform acanthosis with elongated, bulbous rete ridges
2. Alternating ortho- and parakeratosis with Munro microabscesses
3. Hypogranulosis under parakeratotic zones
4. Thinned suprapapillary plates over dilated dermal papillary capillaries
5. Perivascular lymphocytic infiltrate without significant spongiosis
6. Dilated tortuous capillaries in papillary dermis (histologic correlate of Auspitz sign)

Differential Diagnosis

1. Psoriasiform Eczema / Chronic Spongiotic Dermatitis

• Overlapping features: acanthosis, hyperkeratosis, parakeratosis
• Distinguishing from psoriasis: prominent spongiosis, no Munro microabscesses, retained/prominent granular layer, irregular rete ridges, lymphocyte exocytosis rather than neutrophil exocytosis
• In the images shown, spongiosis is notably absent, favoring psoriasis

2. Lichen Simplex Chronicus (LSC)

• Shows acanthosis, hyperkeratosis, hypergranulosis (not hypogranulosis)
• Key difference: LSC has prominent hypergranulosis (thickened granular layer) vs. hypogranulosis in psoriasis; rete ridges are more irregular; no Munro microabscesses
• Dermis shows vertically oriented fibrosis ("fibrosis of collagen bundles")

3. Hypertrophic Lichen Planus

• Can show psoriasiform acanthosis and thick hyperkeratosis
• Key difference: hypergranulosis (prominent granular layer), "saw-tooth" rete ridges, band-like lichenoid lymphocytic infiltrate at the DEJ, Civatte bodies (colloid bodies), vacuolar interface change
• No Munro microabscesses

4. Pityriasis Rubra Pilaris (PRP)

• Can mimic psoriasis; shows follicular plugging, alternating ortho- and parakeratosis in a "checkerboard" pattern
• Key difference: parakeratosis is shoulder-like around follicles ("follicular parakeratosis"), relative preservation of granular layer, no Munro microabscesses, rete ridges less elongated

5. Seborrheic Dermatitis (chronic/thick)

• Parakeratosis more prominent around follicular ostia ("follicular parakeratosis")
• Mild spongiosis present, acanthosis mild to moderate
• No Munro microabscesses

6. Psoriasiform Drug Reaction

• Histologically identical to psoriasis
• May show eosinophils in the infiltrate, less regular rete ridge elongation
• Clinical history of drug intake is key (beta-blockers, lithium, antimalarials, TNF-inhibitors paradoxically)

7. Mycosis Fungoides (Psoriasiform variant)

• Can show psoriasiform epidermal hyperplasia
• Key difference: epidermotropism of atypical large lymphocytes (cerebriform nuclei), Pautrier microabscesses (lymphocytes, not neutrophils), papillary dermal fibrosis, asymmetric perivascular infiltrate ("bare underbelly sign")

Clinicopathological Correlation

• Munro microabscesses (neutrophil collections in stratum corneum) - pathognomonic when present
• Kogoj's spongiform pustule (neutrophilic spongiform intraepidermal pustule in spinous layer) - seen in active psoriasis
• Direct immunofluorescence - stratum corneum autofluorescence in psoriasis (non-specific)
• Clinically: Auspitz sign, silver-white micaceous scale, predilection for elbows/knees/scalp supports psoriasis

Source references: Dermatology 2-Volume Set 5e (Bolognija), p. 3343-3352; Andrews' Diseases of the Skin, p. 1472-1482