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# Lichen planus and interface dermatitis

- Lesion

Lichen planus causes itchy, flat, purple bumps and white lacy patches in the mouth. It is a T-cell attack on the base of the skin.

Updated Nov 12, 2026

## Key points

- Clinical: pruritic, purple, polygonal, planar papules on wrists, shins and genitals; Wickham striae; Koebner phenomenon.
- Oral lichen planus: white reticular (lacy) lesions; erosive forms carry a small risk of squamous cell carcinoma.
- Histology: band-like lymphocytes along the junction, basal vacuolar degeneration, sawtooth rete ridges, wedge-shaped hypergranulosis, compact hyperkeratosis, colloid (Civatte) bodies.
- Max-Joseph spaces: small clefts at the junction from basal damage.
- Associations: hepatitis C (especially oral), drugs (lichenoid drug eruption).
- Discoid lupus: interface damage plus perivascular and periadnexal lymphocytes, follicular plugging, mucin, thick basement membrane; granular IgG and C3 at the junction.

## What it is

Lichen planus is a self-limited (on skin) or chronic (in mouth) inflammatory disease in which cytotoxic T cells attack basal keratinocytes. The clinical «six Ps» (pruritic, purple, polygonal, planar papules and plaques) match a classic band-like lymphocytic infiltrate at the dermoepidermal junction. It belongs to the interface dermatitis family together with lupus erythematosus and erythema multiforme, each with a distinctive twist.

## Step by step

- An unknown antigen (perhaps altered self or viral) is presented by basal keratinocytes or Langerhans cells.
- CD8 cytotoxic T cells accumulate along the dermoepidermal junction.
- They kill basal keratinocytes by apoptosis (Civatte bodies) and vacuolise the basal layer.
- The epidermis responds with hypergranulosis and hyperkeratosis; rete ridges take a sawtooth shape.
- Melanin falls into the dermis and is taken up by macrophages: post-inflammatory hyperpigmentation.

## Interface dermatitides compared

| Disease | Infiltrate | Distinctive features |
| --- | --- | --- |
| [Lichen planus](https://durgical.com/en/conditions/lichen-planus/) | Dense band-like at the junction | Sawtooth rete, hypergranulosis, Civatte bodies |
| [Discoid lupus](https://durgical.com/en/conditions/discoid-lupus-erythematosus/) | Superficial and deep, around vessels and adnexa | Follicular plugging, dermal mucin, thick basement membrane, scarring |
| [Erythema multiforme](https://durgical.com/en/conditions/erythema-multiforme/) | Sparse, superficial | Scattered apoptotic keratinocytes, acute |
| [Lichenoid drug eruption](https://durgical.com/en/conditions/cutaneous-drug-reactions-and-dress/) | Band-like with eosinophils | Parakeratosis, deeper infiltrate |
| [Graft-versus-host disease](https://durgical.com/en/conditions/graft-versus-host-disease/) | Sparse | Satellite cell necrosis after transplant |

## Clinical notes

- Skin lesions often resolve within one to two years, leaving pigmentation; oral disease persists.
- Check hepatitis C status in oral or extensive lichen planus.

## Memory aid

Six Ps on the skin and a sawtooth under the microscope; the T cells cut the bottom row of bricks and leave pink Civatte bodies behind.

## Test yourself

Think of the answer, then tap the question to see it.

## What are Civatte bodies?

Apoptotic basal keratinocytes, seen as round eosinophilic bodies at the dermoepidermal junction in lichen planus.

## Which infection is associated with lichen planus?

Hepatitis C virus infection.

## How does discoid lupus differ histologically from lichen planus?

Lupus has a superficial and deep perivascular and periadnexal infiltrate, follicular plugging, dermal mucin and a thickened basement membrane.

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## Elsewhere in DurgiPedia

- [CD8⁺ cytotoxic T cell](https://durgical.com/en/immunology/cd8-cytotoxic-t-cell/)
- [Apoptosis: the intrinsic and extrinsic pathways](https://durgical.com/en/general-pathology/apoptosis-the-intrinsic-and-extrinsic-pathways/)

## Connections

## Related 4

- [Erythema multiforme, Stevens–Johnson syndrome and TEN](https://durgical.com/en/general-pathology/erythema-multiforme-stevens-johnson-syndrome-and-ten/)
- [Psoriasis and seborrheic dermatitis](https://durgical.com/en/general-pathology/psoriasis-and-seborrheic-dermatitis/)
- [Hepatitis C: why it becomes chronic, and its extrahepatic disease](https://durgical.com/en/general-pathology/hepatitis-c-why-it-becomes-chronic-and-its-extrahepatic-disease/)
- [Aphthous ulcers and reactive oral lesions](https://durgical.com/en/general-pathology/aphthous-ulcers-and-reactive-oral-lesions/)

## Related conditions 4

- [Lichen planus](https://durgical.com/en/conditions/lichen-planus/)
- [Discoid lupus erythematosus](https://durgical.com/en/conditions/discoid-lupus-erythematosus/)
- [Viral hepatitis](https://durgical.com/en/conditions/viral-hepatitis/)
- [Systemic lupus erythematosus](https://durgical.com/en/conditions/systemic-lupus-erythematosus/)

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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](https://medlineplus.gov/skinconditions.html) (MedlinePlus, US National Library of Medicine, 2025).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/general-pathology/lichen-planus-and-interface-dermatitis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/lichen-planus-and-interface-dermatitis/