Lichen planus pigmentosus
LPP is most common in people with intermediate and darker skin colors, is rare in people with lighter skin colors, and has a slightly higher prevalence in women than men. The condition most commonly occurs between the third and fifth decades of life. The time course of LPP is unpredictable, ranging from 6 months to 3 years. The condition is most often described as chronic and progressive with periods of remission and exacerbation. Lesions are usually asymptomatic but can be mildly itchy in some patients.
In LPP, CD8+ autoreactive T cells attack epidermal keratinocytes, leading to an inflammatory lichenoid response. The initial inflammatory infiltrate resolves relatively quickly and leaves behind marked dermal pigmentary incontinence.
LPP has been shown to be more prevalent in patients with hepatitis C virus, diabetes, thyroid disease, and dyslipidemia. Furthermore, 2 Indian studies have linked LPP to the use of mustard oil, amla oil, henna, hair dye, and nickel. Hormonal factors also may play a role as LPP often presents in women around menopause. LPP has also been shown to be triggered by surgery and by COVID-19 vaccination.
L43.8 – Other lichen planus
717061002 – Lichen planus pigmentosus
Differential Diagnosis & Pitfalls
- Ashy dermatosis – Many authors have noted difficulty in distinguishing ashy dermatosis and LPP, and some have argued that the 2 conditions are the same entity.
- Actinic lichen planus – Usually fine scale overlying violaceous lesions in the inflammatory phase.
- Pigmented contact dermatitis
- Nevus of Ota / Hori nevus
- Acquired dermal melanocytosis
- Fixed drug eruption
- Lichenoid drug eruption
- Postinflammatory hyperpigmentation – History of dermatosis.
- Exogenous ochronosis
- Erythromelanosis follicularis faciei et colli – Red-brown patches on the lateral cheeks and neck with tiny, pale follicular papules.
- Idiopathic eruptive macular pigmentation
- Maturational hyperpigmentation