Model Answer
0 min readIntroduction
Lichen Planus (LP) is a chronic inflammatory condition affecting the skin, mucous membranes, hair, and nails. It is an immune-mediated disease with an estimated prevalence of 0.1-1% of the population. Characterized by the “5 Ps” – Papular, Purplish, Pruritic, Polygonal, and Persistent – LP presents with a wide range of clinical manifestations. Understanding the common sites of cutaneous involvement is crucial for accurate diagnosis and appropriate management. This answer will detail the typical locations where LP manifests on the skin, along with characteristic features at each site.
Cutaneous Involvement in Lichen Planus
The skin is frequently involved in Lichen Planus, and the distribution of lesions can vary. The following are the common sites of cutaneous involvement:
1. Flexural Areas
This is the most common site of involvement. The lesions typically appear on the wrists, elbows, ankles, and knees – areas subject to friction and pressure. The lesions are often purplish, flat-topped papules, approximately 2-5mm in diameter. Pruritus (itching) is a prominent symptom.
2. Trunk
The trunk, particularly the upper back and sides, is another frequent site. Lesions here resemble those found in flexural areas, but may be more scattered. Post-inflammatory hyperpigmentation is common after lesion resolution, especially in individuals with darker skin types.
3. Limbs (Extensor Surfaces)
While flexural surfaces are more common, extensor surfaces of the arms and legs can also be affected. The lesions are similar in appearance to those on flexural areas, but may be less intensely pruritic.
4. Face
Facial involvement can occur, particularly around the mouth, forehead, and temples. Lesions can be subtle and may present as slightly raised, reddish-purple papules. In some cases, facial LP can mimic eczema or psoriasis.
5. Scalp
Scalp involvement, known as Lichen Planopilaris (LPP), is a specific subtype of LP that causes scarring alopecia (hair loss). It presents with perifollicular erythema (redness around hair follicles) and scaling, leading to permanent hair loss. Early diagnosis and treatment are crucial to minimize scarring.
6. Nails
Nail involvement is common, occurring in approximately 10-20% of patients with cutaneous LP. Nail changes include longitudinal ridging, thinning, splitting, pterygium (skin growing onto the nail plate), and onycholysis (separation of the nail from the nail bed). Nail involvement can be a significant source of morbidity.
7. Mucous Membranes
Although technically not cutaneous, involvement of mucous membranes (oral, genital, conjunctival) frequently accompanies cutaneous LP. Oral lesions are the most common, appearing as white, lacy patches (Wickham’s striae) on the buccal mucosa. Genital involvement can cause significant discomfort and ulceration.
8. Less Common Sites
- Palms and Soles: LP on palms and soles is less common but can present as thickened, scaly plaques.
- Pressure Points: Areas subject to repeated pressure, such as the shins, can develop lesions.
Variations based on LP subtypes:
- Annular LP: Presents with ring-shaped lesions, often on the trunk and limbs.
- Actinic LP: Occurs on sun-exposed areas and may resemble eczema.
- Linear LP: Presents as a linear arrangement of papules, often following lines of trauma.
Conclusion
In conclusion, Lichen Planus commonly affects flexural areas, the trunk, limbs, face, scalp, and nails. Mucous membrane involvement is also frequent. Recognizing the characteristic features of LP at these sites is essential for accurate diagnosis. Variations in presentation, such as annular, actinic, and linear LP, highlight the diverse clinical spectrum of this condition. Early diagnosis and appropriate management are crucial to minimize morbidity and improve patient quality of life.
Answer Length
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