Skin pathology: terms and reaction patterns
- Topic
Skin is a living barrier with its own immune cells. Pathologists describe its diseases with a small set of words and patterns.
What it is
The skin is the largest organ and a busy immune site. Keratinocytes held together by desmosomes form the barrier and release cytokines; melanocytes give pigment; Langerhans cells and dermal dendritic cells sample antigens; resident memory T cells patrol. Inflammatory skin diseases produce a limited number of reaction patterns, and knowing the vocabulary lets you read any biopsy report.
Function
- Barrier: keratin, lipids and tight junctions prevent water loss and microbial entry.
- Innate defence: keratinocytes make defensins and cathelicidins and release IL-1, IL-6 and TNF when injured.
- Antigen presentation: Langerhans cells carry antigens to lymph nodes.
- Pigment: melanocytes transfer melanin to keratinocytes to shield nuclei from UV light.
- Vitamin D synthesis and thermoregulation.
Inflammatory reaction patterns
| Pattern | What is seen | Typical diseases |
|---|---|---|
| Spongiotic | Intercellular oedema, vesicles | Eczematous dermatitis |
| Psoriasiform | Regular elongation of rete ridges | Psoriasis, chronic eczema, seborrheic dermatitis |
| Interface | Basal vacuoles, apoptotic keratinocytes, lymphocytes | Lichen planus, erythema multiforme, lupus |
| Vesiculobullous | Split at a given level | Pemphigus, pemphigoid, dermatitis herpetiformis |
| Vasculopathic | Vessel wall damage | Leukocytoclastic vasculitis |
| Granulomatous | Epithelioid histiocytes | Sarcoidosis, tuberculosis, leprosy |
| Panniculitis | Inflammation in fat | Erythema nodosum |
Clinical notes
- Clinical words (macule, papule, plaque, vesicle, bulla, pustule, lichenification) pair with these microscopic terms.
- Punch biopsy at the edge of an active lesion gives the most information; blisters need perilesional tissue for immunofluorescence.
Test yourself
Think of the answer, then tap the question to see it.
What is the difference between spongiosis and acantholysis?
Spongiosis is intercellular oedema stretching intact desmosomes; acantholysis is loss of cohesion between keratinocytes from broken desmosomes.
What is parakeratosis?
Retention of nuclei in the stratum corneum, a sign of rapid or abnormal keratinisation (normal only on mucosa).
Which two diseases show an interface pattern?
Lichen planus and erythema multiforme (also lupus erythematosus).
Elsewhere in DurgiPedia
- Skin: epidermis layers, dermis, hypodermis
- Keratinocytes, melanocytes, Langerhans and Merkel cells
- Hair follicles, sebaceous and sweat glands, nails
- Skin examination: primary and secondary lesions
- Dendritic cell (professional antigen-presenting cell)
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Skin Conditions (MedlinePlus, US National Library of Medicine, 2025).
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Representative model, for educational purposes only.