Lichen Planus Pigmentosus: A Clinicopathological Study From Northeast India

Lichen planus pigmentosus (LPP) is an uncommon variant of lichen planus, characterized by the insidious onset of dark brown to gray pigmented macules, mainly in sun-exposed areas and flexural folds. It is mainly reported in Indian, Latino, American, and Middle Eastern patients. This paper aims to document the clinicopathological characteristics of LPP.

A five-year retrospective study from January 2017 to December 2021 analyzed 42 patients diagnosed with LPP who presented with idiopathic, itchy/asymptomatic, hyperpigmented/violaceous macules at the Dermatology outpatient department. The study excluded those with melasma, post-inflammatory pigmentation, or cases where a skin biopsy was unavailable. Demographic, clinical, and histopathological data, including age, sex, residence, site of involvement, pigmentation pattern, and biopsy results, were reviewed. Routine hematoxylin-eosin staining was performed on all biopsies, with special stains such as Masson's trichrome and Congo red used in selected cases to assess fibrosis and to rule out amyloid.

The study involved 42 patients, with a higher prevalence in female patients, 29 (69.0%) compared to 13 (30.9%) male patients, and an average age of 34.2 years. The majority of patients were from urban areas (28, 66.7%), with the most common sites of involvement being the head and neck (14, 33.3%), upper limbs (nine, 21.4%), and back (eight, 19%). Pigmentation patterns were predominantly diffuse (29, 69%), with less common patterns including reticular (seven, 16.7%) and blotchy (four, 9.5%). Histopathological findings included orthokeratosis, epidermal thinning, and melanin incontinence, with Masson's trichrome staining indicating fibrosis in nine (21.4%) cases. Civatte bodies were present in 33 (78.3%) cases. Direct immunofluorescence showed IgM positivity in one of six cases.

LPP is a common pigmentary disorder characterized by persistent, asymptomatic, slaty-gray pigmentation, mainly in sun-exposed areas. Histopathologically, it features orthokeratosis, hypergranulosis, dense dermal lymphocytic infiltrate, melanin incontinence, and frequent Civatte bodies.