Histopathologic Findings in Psoriasis Skin Biopsy
Psoriasis demonstrates a characteristic constellation of histopathologic features dominated by psoriasiform epidermal hyperplasia with regular elongation of rete ridges, parakeratosis with neutrophilic infiltration, dilated tortuous papillary vessels, and hypogranulosis. 1
Classic Histopathologic Features
The most reliable diagnostic features include:
- Psoriasiform epidermal hyperplasia with regular elongation of rete ridges while preserving the rete ridge-dermal papillae pattern 1
- Club-shaped rete ridges (present in 96% of cases) 2
- Hypogranulosis or thinning/absence of the granular layer (96% of cases) 2
- Dermal papilla capillary ectasia with dilated and tortuous blood vessels in the papillary dermis (90% of cases) 2
- Munro microabscesses - collections of neutrophils within the parakeratotic stratum corneum (78% of cases) 2
- Suprapapillary plate thinning - thinning of the epidermis overlying the dermal papillae (63% of cases) 2
- Spongiform pustules of Kogoj - neutrophils within the epidermis associated with spongiosis (53% of cases) 1, 2
Epidermal Changes
Quantitative measurements reveal:
- Marked epidermal thickening with the most prominent increases in palmar regions 3
- Increased corneal layer thickness, particularly pronounced in patients with scalp involvement 3
- Elongated rete ridges, most prominent in knee biopsies (median 491 μm), with 27% greater length in patients without family history 3
- Increased keratinocyte mitotic figures above the basal cell layer 1
Neutrophilic Infiltration Pattern
Neutrophils appear in characteristic locations:
- Subcorneal pustules - neutrophils beneath the cornified layer 1
- Intraepidermal neutrophils forming spongiform pustules 1
- Parakeratotic horn layer containing neutrophils 1
- Dermal neutrophils (69% of cases) 2
Expanded Histopathologic Spectrum
Recent evidence demonstrates that psoriasis exhibits a broader histopathologic spectrum than traditionally recognized, and the presence of non-classic features does not exclude the diagnosis. 2
Non-classic but commonly observed features include:
- Irregular acanthosis (84% of cases) rather than regular acanthosis 2
- Junctional vacuolar alteration (76% of cases) 2
- Spongiosis (76% of cases) 2
- Necrotic keratinocytes (67% of cases) 2
- Paradoxical hypergranulosis (65% of cases) despite hypogranulosis being considered classic 2
- Neutrophilic spongiosis (61% of cases) 2
- Dermal eosinophils (49% of cases) 2
- Compact orthokeratosis (37% of cases) 2
- Papillary dermal fibrosis (35% of cases) 2
- Lichenoid infiltrate (25% of cases) 2
Immunopathologic Context
The histopathologic presentation reflects the underlying immune mechanisms:
- Adaptive immune responses predominate in chronic plaque psoriasis 4
- Innate and autoinflammatory responses predominate in pustular variants 4
- The balance between autoimmune and autoinflammatory components determines the clinical and histopathological presentation 4
Clinical-Pathologic Correlation
Histopathological examination remains the main diagnostic tool in atypical and controversial conditions where clinical aspects are not sufficiently indicative. 4
- Biopsy is rarely required for classic psoriasis with typical distribution 4
- Early or resolving lesions may show subtle psoriasiform changes 1
- Different body sites show varying degrees of histologic changes, with palmar regions showing the most prominent epidermal thickening 3
Critical Diagnostic Pitfall
Only non-classic or refractory cases tend to be biopsied, creating diagnostic uncertainty when encountering non-classic features. 2 Dermatopathologists should recognize that irregular acanthosis, spongiosis, vacuolar changes, and even hypergranulosis can occur in clinically confirmed psoriasis and do not exclude the diagnosis 2.