Major histopathological changes in the epidermis — expanded notes
How to approach an epidermal biopsy
First identify the dominant reaction pattern: spongiotic, psoriasiform, lichenoid/interface, acantholytic, vesiculobullous, granulomatous or neoplastic. Then assess stratum corneum, granular layer, spinous layer, basal layer, dermoepidermal junction and inflammatory cell type.
Spongiotic pattern
Spongiosis is intercellular oedema between keratinocytes. Early disease shows widened spaces and stretched desmosomes; severe spongiosis may form intraepidermal vesicles. It is typical of eczema, including atopic, allergic contact and irritant dermatitis. Eosinophils may suggest allergic or drug-related disease but are not specific.
Psoriasiform pattern
Psoriasiform hyperplasia shows regular elongation of rete ridges and thickening of epidermis. Psoriasis typically has parakeratosis, diminished granular layer, suprapapillary thinning, dilated tortuous papillary vessels and neutrophils in the stratum corneum (Munro microabscesses) or epidermis (spongiform pustules of Kogoj).
Interface pattern
Interface dermatitis targets basal keratinocytes. Vacuolar change, apoptotic keratinocytes and pigment incontinence may occur. A band-like lichenoid lymphocytic infiltrate is typical of lichen planus. Lupus may show interface change with dermal mucin and periadnexal inflammation.
Acantholytic and blistering patterns
Acantholysis is loss of keratinocyte cohesion. Pemphigus vulgaris classically produces suprabasal acantholysis; pemphigus foliaceus produces superficial subcorneal acantholysis. Bullous pemphigoid produces a subepidermal blister with eosinophils and linear IgG/C3 at the basement membrane zone on direct immunofluorescence. Histological level and immunofluorescence are essential to classification.
Other epidermal findings
- Koilocytosis: perinuclear halo and nuclear irregularity, supporting HPV effect.
- Dysplasia: atypical keratinocytes, disordered maturation and abnormal mitoses; actinic keratosis shows atypia often beginning in lower epidermis.
- Necrotic keratinocytes: may occur in interface dermatitis and severe drug reactions.
- Epidermotropism: atypical lymphocytes within epidermis; assess for mycosis fungoides in the correct clinical context.