Dermatology, Venereology and Leprosy
Lichen Planus
Lichen planus for MBBS and NEET-PG: six-P morphology, Wickham's striae, oral, nail and scalp variants, band-like histology, drug mimics and treatment, mapped to NMC codes DR4.
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Lichen Planus
Lichen planus for MBBS and NEET-PG: six-P morphology, Wickham's striae, oral, nail and scalp variants, band-like histology, drug mimics and treatment, mapped to NMC codes DR4.
Lichen planus is the classic lichenoid eruption and a common pairing with psoriasis in examinations. This chapter covers the six-P morphology, Wickham's striae, the mucosal, nail and scalp variants, the band-like histology, and the treatment of an often self-limiting but sometimes erosive disease.
High-yield: Lichen Planus
- Lichen planus is a T-cell-mediated inflammatory disorder of skin and mucosa, remembered by the six Ps: purple, pruritic, polygonal, planar, papules and plaques.
- The papules are violaceous and flat-topped and are crossed by fine white lines called Wickham's striae.
- Common sites are the flexor wrists, forearms, ankles and the lower back.
- The Koebner phenomenon produces lesions in a linear arrangement along a scratch.
- Oral lichen planus shows a lacy white network on the buccal mucosa and can be erosive and painful.
- Nail involvement can cause longitudinal ridging and, in severe cases, a pterygium as the nail fold scars onto the nail bed.
- Scalp involvement, lichen planopilaris, causes a scarring alopecia with permanent hair loss.
- Histology shows a band-like lymphocytic infiltrate at the dermo-epidermal junction with saw-toothing of the rete ridges and basal cell degeneration.
- Post-inflammatory hyperpigmentation is prominent after lesions resolve, particularly in darker skin.
- Lichenoid drug eruptions from agents such as antimalarials, thiazides, beta-blockers and gold can mimic idiopathic lichen planus.
- An association with hepatitis C is recognised, so testing may be appropriate in some patients.
- Erosive and long-standing oral lichen planus carries a small risk of malignant transformation and needs monitoring.
- Most cutaneous lichen planus is self-limiting and settles within one to two years.
- Topical corticosteroids are first-line, with systemic steroids or other agents reserved for widespread or erosive disease.
Lichen planus at a glance
- **Morphology (six Ps):** Purple, pruritic, polygonal, planar papules and plaques with Wickham's striae.
- **Sites:** Flexor wrists, forearms, ankles, lower back; oral, nail and scalp variants.
- **Histology:** Band-like junctional lymphocytes, saw-tooth rete ridges, basal degeneration.
- **Mimics:** Lichenoid drug eruption; check drugs and consider hepatitis C.
NMC competencies in this chapter
- **DR4.1:** Distinguishing lichen planus lesions from other causes
- **DR4.2:** Clinical features and management of lichen planus
Frequently Asked Questions
What are the six Ps of lichen planus?
Purple, pruritic, polygonal, planar papules and plaques. The lesions are violaceous, flat-topped and itchy, and are crossed by fine white lines called Wickham's striae.
What are Wickham's striae?
They are fine white lacy lines seen on the surface of lichen planus papules and on the buccal mucosa, and they are a helpful diagnostic clue.
Which drugs cause a lichenoid eruption?
Antimalarials, thiazide diuretics, beta-blockers, gold and some others can produce a lichenoid drug eruption that closely mimics idiopathic lichen planus, so a drug history is important.
Is lichen planus dangerous?
Cutaneous lichen planus is usually self-limiting, but erosive and long-standing oral disease carries a small risk of malignant change and should be monitored.
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