Describe the characteristic histopathologic features of classic Lichen planus. - The stratum corneum is thickened (hyperkeratotic), but is largely devoid of retained keratinocytic nuclei (essentially no parakeratosis).
- The granular layer is focally accentuated (“wedge-shaped” hypergranulosis).
- The Malpighian layer (stratum spinosum and stratum granulosum) is irregularly thickened, demonstrating a “sawtooth” acanthosis, with occasional necrotic keratinocytes in the superficial dermis (Civatte bodies).
- The basal layer is disrupted and appears lost or flattened (“interface reaction”).
- The dermal–epidermal junction is vacuolated and obscured by a “bandlike” lymphocytic inflammatory infiltrate. This pattern of infiltration is so typical of LP, it is referred to as a “lichenoid infiltrate.”
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