Summary

Lichen planus (LP) is a T-cell-mediated inflammatory disorder affecting the skin, mucous membranes, hair, and nails. The classic cutaneous form presents with the "6 Ps": Purple, Polygonal, Planar (flat-topped), Pruritic Papules and Plaques. Wickham's striae (fine white lines on the surface) are pathognomonic. LP commonly affects the flexor wrists, lower back, ankles, and oral mucosa. The Koebner phenomenon (lesions at sites of trauma) is characteristically seen. The condition is often self-limiting (1-2 years for skin), but oral and genital mucosal disease can persist and cause significant morbidity. Treatment is with potent topical steroids.

Key Facts

• 6 Ps: Purple, Polygonal, Planar, Pruritic Papules/Plaques
• Wickham's Striae: White lacy network on surface
• Koebner Phenomenon: Lesions at trauma sites
• Sites: Flexor wrists, ankles, lower back, oral mucosa
• Duration: Skin LP usually self-limiting (1-2 years); Mucosal LP persists longer
• Treatment: Potent topical steroids (Clobetasol)

Clinical Pearls

"6 Ps": The classic mnemonic - Purple, Polygonal, Planar, Pruritic Papules and Plaques.

"Wickham's Striae = Lichen Planus": These fine white lines on papules are virtually diagnostic. Use dermoscopy to see them.

"Oral LP is Common": 50% of skin LP patients have oral involvement. Always check the mouth.

"Hepatitis C Link": There is an association with Hepatitis C, especially in Mediterranean and Japanese populations. Consider screening.

Skin

• Violaceous, flat-topped papules
• Wickham's striae (use dermoscopy)
• Koebner phenomenon

Oral

• White lacy network (buccal mucosa most common)
• Erosions if erosive variant
• Check tongue, gingiva

Nails

• Ridging, thinning
• Pterygium (scarring of nail fold to nail bed)

Scalp

• Follicular papules
• Scarring alopecia (lichen planopilaris)

Natural History

• Cutaneous LP: Resolves in 1-2 years in most (85%)
• Oral LP: Persists longer (may be lifelong)
• Nail/scalp LP: Often progressive

Recurrence

• 15-20% recur after resolution

Key Guidelines

1. British Association of Dermatologists: Lichen Planus Guidelines
2. European Guidelines on Oral Mucosal Diseases

Key Evidence

Treatment

• Topical steroids: First-line with good evidence
• Tacrolimus: Effective for mucosal disease

What is Lichen Planus?

Lichen planus is a skin condition that causes itchy, purple, flat-topped bumps. It can also affect the mouth, nails, and scalp. It's not contagious.

What Does It Look Like?

• Small, shiny, purple-pink bumps on the skin
• White lacy patterns inside the mouth
• Nail ridging or thinning
• Hair loss on the scalp (if it affects hair follicles)

What Causes It?

The immune system attacks the skin, but we don't fully understand why. It's sometimes linked to hepatitis C or certain medications.

How is it Treated?

• Strong steroid creams (main treatment)
• Steroid mouthwash or gel for oral lesions
• Light therapy for widespread skin involvement

How Long Does it Last?

Most skin cases clear up within 1-2 years. Mouth involvement can last longer. The skin may be left with darker marks for a while after the rash clears.