Lichen Planus
Dermatology
Illness script · Dermatology
Lichen Planus
Chronic T-cell–mediated inflammatory disorder of skin, mucous membranes, nails, and hair, classically producing pruritic violaceous flat-topped papules.
This illness script for Lichen Planus covers predisposing factors, classic presentation, mechanism, workup, management, and the clinical pivots that separate it from look-alikes—written for USMLE Step 1 and clerkship reasoning.
01
Predisposing factors
- Peak incidence ages 30–60; women slightly predominate, especially oral LP
- Strong association with hepatitis C virus infection
- Lichenoid drug reactions: thiazides, beta-blockers, NSAIDs, antimalarials, ACE inhibitors
- Autoimmune associations: thyroid disease, primary biliary cholangitis
- Psychological stress can trigger or exacerbate flares
02
Presentation
- Classic 6 P's: Pruritic, Purple, Polygonal, Planar, Papules, Plaques
- Wickham striae: white lacy lines on papule surface — pathognomonic
- Koebner (isomorphic) phenomenon: new lesions at sites of trauma
- Predilection for flexor wrists, ankles, lumbar back, and shins
- Oral LP: white reticular lace-like pattern on buccal mucosa (most common mucosal site)
- Nail LP: dorsal pterygium (nail fold fusing to nail bed) is pathognomonic
03
Pathophysiology
- CD8+ cytotoxic T cells aberrantly attack basal keratinocytes at the dermoepidermal junction
- Basal cell apoptosis produces Civatte (colloid) bodies on histology
- Band-like subepidermal lymphocytic infiltrate causes saw-tooth rete ridge pattern
- Exact autoantigen unknown; molecular mimicry with HCV proposed
04
Diagnostics
- Clinical diagnosis confirmed by 6 P's + Wickham striae
- Skin biopsy (gold standard): band-like lymphocytic infiltrate, saw-tooth rete ridges, Civatte bodies
- DIF: fibrinogen/IgM deposits at dermoepidermal junction (shaggy pattern)
- Always order hepatitis C serology in newly diagnosed LP
- KOH prep to exclude tinea; oral swab/culture to exclude candidiasis
05
Management
- Topical high-potency corticosteroids: first-line for localized cutaneous LP
- Topical tacrolimus or pimecrolimus: preferred for oral and genital LP (steroid-sparing)
- Systemic corticosteroids or acitretin for widespread or refractory disease
- Narrowband UVB or PUVA phototherapy for generalized skin involvement
- Monitor erosive oral LP long-term — carries ~1–3% risk of squamous cell carcinoma transformation
06
Clinical pivots
How to separate this script from the look-alikes that show up on exams and on the wards.
Psoriasis
LP has flat-topped violaceous papules with Wickham striae on flexors; psoriasis has silver-white scales on extensor surfaces with Auspitz sign.
Oral candidiasis (thrush)
LP white oral plaques cannot be scraped off; candidiasis pseudomembrane wipes away easily, leaving erythematous base.
Secondary syphilis
Secondary syphilis causes a maculopapular rash on palms and soles with positive RPR/VDRL; LP spares palms/soles and is seronegative.
Lichenoid drug reaction
Identical histology, but drug reaction lacks Wickham striae, is more widespread/photodistributed, and resolves after offending drug is stopped.
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Educational use only. This illness script is a study framework, not medical advice. Confirm decisions with current guidelines and your clinical supervisors.