Lichen Planus and Psoriasis: Distinguishing Between Skin Conditions

April 20, 2024

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Lichen planus and psoriasis are two common inflammatory skin conditions that can present significant diagnostic and therapeutic challenges for dermatologists and patients alike. Though distinct entities, they share intriguing overlaps in pathogenesis, morphology, and management that warrant a deeper analysis through the lens of evidence-based dermatology.

An Introduction to the Overlapping Worlds of Lichen Planus and Psoriasis

Psoriasis and lichen planus (LP) exemplify the complex intersection of inflammatory dermatoses. Once viewed as discrete conditions, emerging insights into their autoimmune underpinnings and ability to clinically mimic each other have shattered the illusion that they exist in isolation within the vast spectrum of papulosquamous skin disorders.

This content explores the interconnected nature of psoriasis and LP – from the immunopathological clues under their deceptive surfaces to the therapeutic conundrums posed by their coexistence. We shine the spotlight on their areas of distinction and overlap, equipping dermatologists, patients and the general public with accurate, experience-driven perspectives on these two common dermatoses that increasingly appear in unison.

PsoriasisLichen Planus
Inflammatory skin conditionInflammatory skin condition
Autoimmune disorderAutoimmune disorder

First, we cover the fundamentals of psoriasis pathology and lichen planus pathogenesis independently before contrasting their clinical and histological manifestations side by side. We summarize the latest guidelines on treating them individually while addressing the management dilemmas that crop up when they co-exist.

Equipped with this synthesis of evidence and insights from experts in dermatology, our discourse on lichen planus and psoriasis aims to empower readers to separate the signals from the noise regarding these two overlapping dermatologic conditions.

Demystifying the Pathogenesis of Psoriasis and Lichen Planus

Though their clinical features differ, psoriasis and LP share fundamental autoimmune traits – from genetic risk factors to the central role of T cells in propagating inflammation.

What Drives Psoriasis Pathogenesis?

Psoriasis is an autoimmune condition driven by multiple intersecting pathways with both genetic and environmental triggers. It manifests as raised, thick, red skin plaques covered by flaky, silver-white scales.

While its exact pathogenesis remains unclear, the bulk of evidence implicates the activation of inflammatory T cells in the skin as the cardinal event. Key aspects include:

  • Dendritic cell activation
  • TH1 and TH17 cell stimulation
  • Production of inflammatory cytokines like TNF-alpha, IL-23, IL-17 and IFN-gamma
  • Keratinocyte hyperproliferation

Genetic analysis also reveals allelic variants related to skin barrier function, innate immunity, and NF-kB signaling as culprits. Environmental factors like infections and medications can further stimulate these inflammatory networks.

Ultimately, the interplay between activated T cells and signaling pathways drives the development of psoriatic lesions throughout the skin.

What Triggers Lichen Planus Inflammation?

Lichen planus (LP) features shiny, flat-topped, violaceous skin papules and plaques that resemble lichen. Mucosal surfaces frequently exhibit similar lesions.

Although less studied than psoriasis, emerging evidence suggests LP also has autoimmune origins – mediated chiefly by T cells. Key aspects include:

  • Activation of antigen-specific cytotoxic CD8+ T cells
  • Recognition of epidermal antigens
  • Produce inflammatory cytokines like IFN-gamma
  • Promote apoptosis of keratinocytes through Fas-Fas ligand binding

Notably, both CD4+ and CD8+ T cells infiltrate lichen planus skin lesions with clonal expansion. Genetic associations also parallel psoriasis, encompassing HLA alleles and killer cell immunoglobulin receptors that govern cytotoxic T cell responses.

Lichen Planus vs Psoriasis: Key Similarities and Differences

Despite similarities in their immune pathogenesis, lichen planus, and psoriasis vary across clinical and histological manifestations, helping distinguish them:

Clinical FeaturePsoriasis VulgarisLichen Planus
Primary lesionsWell-demarcated erythematous plaques covered by silver-white scalesPolygonal, shiny, flat-topped pink, purple or skin-colored papules
Surface textureThick, dry scales giving an uneven “stucco-like” textureSmooth, shiny surface described as “lacquered” or “varnished.”
DistributionExtensor surfaces like elbows, knees, scalp and lower backFlexural surfaces of the wrists, shins and genitals
ItchMildIntense pruritus
Koebner phenomenonPresentAbsent
Mucosal involvementUncommonFrequent erosive lesions in the oral cavity
Nail changesPitting and oil drop discolorationAtrophic longitudinal ridging

Furthermore, they differ on histology:

  • Psoriasis shows epidermal thickening, regular elongation of rete ridges and collections of neutrophils forming spongiform pustules of Kogoj.
  • Lichen planus features a band-like lymphocytic infiltrate, Damage of the basal cell layer leads to apoptotic keratinocytes termed “colloid or Civatte bodies”.

These salient differences guide the accurate diagnosis of both entities.

The Therapeutic Perspective on Lichen Planus and Psoriasis

We summarize recommended treatment guidelines for lichen planus and psoriasis as independent conditions:

Treating Lichen Planus

Based on lesion severity and morphology, lichen planus management options encompass:

  • Topical corticosteroids (potent agents for widespread disease)
  • Intralesional corticosteroids (for isolated thick plaques)
  • Systemic corticosteroids (for rapidly progressive LP)
  • Phototherapy using narrowband UVB or PUVA
  • Alternative therapy with acitretin, methotrexate or mycophenolate

Refractory, mucosal and eruptive disease poses higher treatment hurdles in lichen planus.

Addressing Psoriasis

Options for managing psoriasis encompass:

  • Topical agents like corticosteroids, Vitamin D analogs and calcineurin inhibitors
  • Phototherapy with UVB, narrow band UVB and PUVA
  • Systemic therapy including methotrexate, acitretin and cyclosporine
  • Biologics that inhibit TNF, IL-17, IL-23 and other targets
  • Complementary medicine like dietary modifications and stress reduction techniques

Depending on body surface area, exposed parts and quality of life issues, physicians customize management.

The Added Twist of Coexistent Disease

When lichen planus and psoriasis coincide, integrating treatment poses dilemmas:

  • NB-UVB works for both, but higher cumulative dosages needed for psoriasis may induce flares of lichen planus through antigen exposure.
  • Acitretin shows efficacy in both individually but can also worsen LP.
  • Some biologics like anti-TNF inhibitors demonstrate short-term improvement but risk precipitating LP during long-term utilization for psoriasis.

Therefore, dermatologists must tailor therapy to each patient by considering the predominant and more clinically severe disease, while monitoring for changing patterns in this delicate balancing act.

Frequently Asked Questions on Lichen Planus and Psoriasis Overlap

Here are some common questions that arise regarding the coexistence of lichen planus and psoriasis:

Is the relationship between lichen planus and psoriasis just a coincidence?

No. Emerging analyses reveal significant epidemiological overlaps between lichen planus and psoriasis – suggesting common environmental or immunopathological triggers influence their co-development. Studies report coincidence rates ranging from 1.4% to 5%.

How can I tell them apart?

Careful examination of skin and scalp lesions coupled with histological analysis of biopsy samples helps distinguish lichen planus and psoriasis. The former features violaceous, pruritic, polygonal smooth papules/plaques lacking scale while the latter manifests as well-demarcated erythematous scaly plaques in extensors.

If I have lichen planus, am I at higher risk for developing psoriasis?

Yes. Having lichen planus raises odds of developing psoriasis and vice versa. Analyses reveal 2 – 5% of lichen planus patients eventually develop psoriasis – beyond reported coincidence rates. This provides avenues for exploring pathogenic overlaps via future studies.

What’s the best approach to treating them when they coincide?

No consensus exists currently. With overlapping treatment options, experts suggest matching therapies to the predominant condition, starting gently then escalating as needed. When systemic agents or biologics are utilized to treat psoriasis in this scenario, vigilant monitoring for lichen planus flares becomes necessary.

What does the coexistence of lichen planus with psoriasis mean for my long-term prognosis?

Studies reveal that when lichen planus occurs with psoriasis, patients report more widespread disease, higher use of systemic therapy and greater likelihood of flares or persistent lesions. More research on prognostic and pathogenic markers in coexistent disease will shed light on any differences in long-term outcomes.

In Summary: Key Highlights on the Psoriasis-Lichen Planus Relationship

  • Lichen planus and psoriasis illustrate the overlap between inflammatory skin conditions with autoimmune origins.
  • Both feature activated, inflammatory T cell pathways that trigger keratinocyte changes and lesions.
  • They differ on clinical features and distribution but also share common treatments like NB-UVB and topical steroids.
  • When concurrent, therapeutic challenges may emerge, needing customization.
  • Further research on triggers and markers of coexistence can shape management for better long-term outcomes.

Thus, while lichen planus and psoriasis have distinct identities, their worlds collide much more than once believed. Continued exploration of their points of convergence – from cell signals to skin manifestations – will unravel mysteries benefitting dermatology and dermatopathology practice.


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