Summary

Lichen planus (LP) pigmentosus is a rare variant of cutaneous lichen planus (see this term) characterized by the presence of hyperpigmented lichenoid lesions in sun-exposed or flexural areas of the body.

The overall prevalence is unknown. LP pigmentosus is a rare disease in Europe but it is common in Indian populations and in the Middle East. There is no difference in distribution between males and females.

The disease usually appears in the third and fourth decade of life. The lesions are asymptomatic or mildly pruritic. Skin changes are dark brown or slate grey macules or papules with, in most cases, a diffuse pigmentation pattern. They most commonly affect the face, neck and upper limbs. Predominantly intertriginous disease, usually of the axillae and groins (described mostly in Caucasians), has been termed lichen planus pigmentosus inversus. The scalp, nails or mucosa are not affected. LP pigmentosus can exist in association with typical LP lesions. Histological features of LP pigmentosus are similar but milder than classic LP, with a lichenoid interface reaction, vacuolar change and apoptotic keratinocytes. Melanin incontinence is prominent, and may be the only feature of older lesions; it may extend deeper into the dermis than typical post-inflammatory pigmentation.

Etiology is unknown but various factors (e.g. viral infections and certain topical agents including mustard oil, amla oil and henna hair dyes) can trigger the disease. One case has been reported in association with Bazex syndrome (see this term) and head and neck cancer.

Lichen planus pigmentosa seems to follow a chronic progressive course.

Expert reviewer(s)

• Dr Stephanie ARNOLD
• Dr Susan COOPER