Lichen planus (discussed in detail in Chapter 5) is a disease that generally presents as a white lesion, with variants showing red and desquamative lesions. Rarely, erosive lichen planus can be associated with diffuse melanosis.
In such instances, the classic lesions of lichen planus remain recognizable, usually in the buccal mucosa and vestibule. Reticulated white patches, with or without a red erosive component, overlie or are flanked by diffuse brown macular foci (Figure 6-9). This increase in melanogenesis may be stimulated by the infiltrate into the basal layer of T lymphocytes that contribute to basal cell degeneration. Histologically, the usual features of lichen planus are observed, along with basilar melanosis and melanin incontinence.