## Lichen Planus: Etiopathogenesis and Course **Key Point:** While hepatitis C virus (HCV) is associated with lichen planus in some geographic regions (particularly the Mediterranean and Asia), it is **NOT a universal causative agent** and is not found in all regions. The association is epidemiologically variable, not a proven causative relationship in all cases. ### Pathogenesis and Risk Factors | Aspect | Details | Evidence | |--------|---------|----------| | **Immune mechanism** | CD8+ T-cell mediated; targets basal keratinocytes | Well-established; central to pathogenesis | | **HCV association** | Regional variation; strong in Mediterranean/Asia; weak/absent in Northern Europe/North America | Geographic-dependent; not universal | | **Other triggers** | Contact allergens, drugs (ACE inhibitors, NSAIDs, antimalarials), graft-versus-host disease | Documented but variable | | **Autoimmune basis** | Lichenoid tissue reaction; T-cell infiltration at BMZ | Confirmed by histology and immunology | **High-Yield:** HCV is associated with LP in certain populations (Mediterranean, Japanese cohorts) but is NOT a universal causative agent. In many Western populations, HCV seropositivity in LP patients is no higher than in controls. ### Natural History and Prognosis **Cutaneous lichen planus:** - Spontaneous remission in 60–70% of patients within 1–2 years - Chronic course in 15–20% of patients - Recurrence possible after apparent remission **Oral lichen planus:** - More persistent than cutaneous disease - Malignant transformation risk: 0.5–5% over 10 years (varies by study) - Erosive form carries higher transformation risk than reticular form **Clinical Pearl:** Erosive oral lichen planus requires closer surveillance due to increased malignancy risk. Patients should be counseled about smoking and alcohol cessation, which are additional risk factors for transformation. **Warning:** Do not assume HCV is the cause of lichen planus in all patients. Serology should be checked in endemic regions, but a negative result does not exclude LP. ### Why the Other Options Are Correct 1. **Oral LP malignancy risk** — Well-documented; 0.5–5% risk of transformation to SCC over 10 years. 2. **Cutaneous LP resolution** — Typical course is spontaneous remission within 1–2 years in most patients. 3. **CD8+ T-cell mediated** — Central to LP pathogenesis; CD8+ lymphocytes target basal keratinocytes in a lichenoid reaction. [cite:Harrison 21e Ch 297]
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