Introduction: 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.
Materials and methods: 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.
Results: 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.
Conclusion: 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.
Keywords: diffuse; histopathology (hp); lichen planus pigmentosus; melanin incontinence; skin pigmentation.
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