# Lichen Planus Pigmentosus and Ashy Dermatosis

> NEET-PG Dermatology notes on lichen planus pigmentosus and ashy dermatosis, covering slate-grey pigmentation in Indian skin and its differential diagnosis.

- Canonical URL: https://prepelephant.com/topics/neet-pg/dermatology/lichen-planus-pigmentosus-and-ashy-dermatosis
- Exam / course: NEET-PG · Subject: Dermatology
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-15
- Last updated: 2026-10-15
- Reference basis: IADVL Textbook of Dermatology; Fitzpatrick's Dermatology; Rook's Textbook of Dermatology
- How to cite: "Lichen Planus Pigmentosus and Ashy Dermatosis", PrepElephant, https://prepelephant.com/topics/neet-pg/dermatology/lichen-planus-pigmentosus-and-ashy-dermatosis

## Direct answer

Lichen planus pigmentosus is a pigmented variant of lichen planus producing slate-grey macules and reticulate patches, mainly on the face, neck and flexures. Ashy dermatosis is a closely related grey-blue pigmented eruption that usually affects the trunk and limbs, and many authors regard it as overlapping with erythema dyschromicum perstans. Both respond slowly to topical therapy and must be separated from melasma and drug-induced pigmentation.

## What you must remember

- **Lichen planus pigmentosus:** a pigmented lichenoid eruption of slate-grey macules and reticulate patches, typically on the face, neck and flexures.
- **Ashy dermatosis:** grey or blue-grey macules, usually on the trunk and limbs, often considered synonymous with erythema dyschromicum perstans.
- **Histology:** interface (lichenoid) change with basal vacuolar degeneration, a band-like lymphocytic infiltrate and pigment incontinence.
- **Setting:** the condition is commonly reported in people with darker skin, including many Indian patients, and women are often affected.
- **Mucosa:** oral lesions and Wickham striae are typically absent, which distinguishes it from classic lichen planus.
- **Differential:** melasma, minocycline pigmentation, confluent and reticulated papillomatosis and post-inflammatory hyperpigmentation.
- **Photoprotection:** ultraviolet exposure worsens the pigment, so sunscreen and sun avoidance form part of every plan.
- **Treatment:** topical corticosteroids, calcineurin inhibitors, retinoids and hydroquinone are used, with a variable and slow response.

## Distinguishing grey pigmentation of the face

A 34-year-old woman has grey-brown reticulate macules on the cheeks and neck that have worsened over two years despite sunscreen use. The table compares the commonest mimics, and the decisive clues are the pattern, the colour and the histology.

| Condition | Typical pattern | Discriminating clue |
|---|---|---|
| Lichen planus pigmentosus | Slate-grey reticulate macules on face, neck and flexures | Interface lichenoid change on biopsy |
| Melasma | Brown, symmetrical patches over malar area and forehead | Pigment with melanophages but no interface change |
| Minocycline pigmentation | Blue-grey pigment, often on the face and scars | Drug history; pigment persists after withdrawal |
| Confluent and reticulated papillomatosis | Brown reticulate papules on upper trunk | Papillomatous surface and midline distribution |
| Ashy dermatosis | Grey-blue macules on trunk and limbs | Trunk distribution, with facial involvement less typical |

Histology is the most useful separator between lichen planus pigmentosus and melasma, since the former shows an interface reaction. A careful drug history is equally important, because minocycline pigmentation can closely resemble the disease.

## Where the exam tries to catch you

Grey pigmentation questions test the pattern, the drug history and the histology rather than the colour alone.

- **Trap:** diagnosing every grey pigmented face in an Indian woman as melasma. **Correct:** melasma is brown and symmetrical, whereas lichen planus pigmentosus is slate-grey, reticulate and lichenoid on biopsy.
- **Trap:** missing a drug cause such as minocycline. **Correct:** a drug history must be taken, since minocycline pigmentation can mimic this condition and may persist after withdrawal.
- **Trap:** expecting lichen planus pigmentosus to clear with sunscreen alone. **Correct:** sun protection prevents progression, but established lesions need topical therapy and respond slowly.

## Frequently asked questions

### What is the typical distribution of lichen planus pigmentosus?

Lichen planus pigmentosus typically involves the face, neck and skin folds, with slate-grey macules that often coalesce into reticulate patterns. Oral lesions are usually absent, which helps separate it from classic lichen planus.

### How does ashy dermatosis differ from lichen planus pigmentosus?

Ashy dermatosis usually involves the trunk and limbs, whereas lichen planus pigmentosus favours the face, neck and flexures. Many authors treat ashy dermatosis as synonymous with erythema dyschromicum perstans, and the two entities overlap, so books differ in how strictly they separate them.

### What histological feature supports the diagnosis of lichen planus pigmentosus?

Interface lichenoid change, with basal layer vacuolar degeneration and a band-like lymphocytic infiltrate, supports the diagnosis of lichen planus pigmentosus. Pigment incontinence, with melanophages in the dermis, is also seen and helps separate it from melasma.

### Which drug can cause slate-grey pigmentation that mimics lichen planus pigmentosus?

Minocycline is the best-known cause of slate-grey or blue-black pigmentation, which can closely resemble lichen planus pigmentosus. The pigment can persist after the drug is stopped, so a detailed drug history is essential before a diagnosis is made.