Lichen planus-like keratosis
Lichen planus-like keratosis, also known as LPLK and lichenoid keratosis, is one of the common benign neoplasms of the skin. It is believed to be either a seborrheic keratosis or a solar lentigo that is undergoing regression. Supporting evidence has been published beginning with Mehregan’s findings of the presence of lentiginous epidermal hyperplasia in lesions interpreted as LPLK. Further supporting evidence can be found by Laur, et al who in 1981 published a detailed clinical-histopathologic correlation in the JAAD . In addition, Goldenhersh et al , described performing biopsies of lentigines on two instances. The first being a biopsy of a solar lentigo and 5 years later, after the lesion had demonstrated a clinical change into a solitary lichen planus‐like keratosis.
Clinical and Histologic Appearance
Lichen planus-like keratosis is a great masquerader with a differential diagnosis including basal cell carcinoma, squamous cell carcinoma and melanoma. The wide differential diagnosis is due to the extreme variability in characteristic appearance with many pigmentation and morphologic possibilities. The clinical appearance depends on its stage of evolution.
The lesion can appear as a macule or papule that is pink, pinkish brown, pinkish orange, rust colored, purplish brown, dusky violaceous or blue-gray to black. Some lesions are characterized by a velvety appearance, some have a fine scale, while others have accentuated skin markings. Lesions can be solitary or in some cases multiple.
The histologic features of early stage of LPLK include hypergranulosis, epidermal hyperplasia, a few necrotic keratinocytes and a superficial, bandlike lichenoid infiltrate. Clinically these lesions appear as pink macules or papules and may be difficult to distinguish from basal cell carcinoma or squamous cell carcinoma.
Histologically intermediate stage LPLK is characterized by melanophages, inflammatory cells and fibrosis, with features consistent with either a lentigo or a seborrheic keratosis. In some cases, clinically, the lesion may be difficult to distinguish from melanoma (melanoma on sun-damaged skin, lentiginous melanoma, lentigo maligna melanoma).
Late stage LPLK is characterized histologically by papillary fibrosis, telangiectasias, and melanophages. The lesions have a more blue-gray to black clinical appearance and may be difficult to distinguish from melanoma.
Dermoscopy allows the detailed visualization of the structures found within the epidermis, dermoepidermal junction and papillary dermis. This information creates a bridge between the clinical and histologic correlates, thus narrowing the differential and allowing for a more accurate assessment of the lesion.
Early Stage LPLK
Lichen planus-like keratosis in its early stage is characterized by polymorphous vessels: dotted vessels and short thin vessels that are either linear, slightly curved or serpentine in appearance. The lesions may appear structureless, pink-white with an orange or yellow hue, colors that are not bright nor saturated, borders that are scalloped and a scale. Shiny white structures (SWS, or crystalline structures) are commonly seen with LPLK, that appear as white strands or blotches. Rosettes can also be seen with LPLKs that coincide with actinically damaged skin.
Here are two examples of early stage LPLKs:
Intermediate Stage LPL
Lichen planus-like keratosis in the intermediate phase is characterized by two patterns. The first pattern depicts the dermoscopic features of a solar lentigo (fine lines parallel; straight, slightly curved, long or short, with sharply demarcated and scalloped borders) with the addition of regression structures: focal gray dots/granules.
The second pattern portrays the features of a seborrheic keratosis (borders sharply demarcated, milia-like cysts, comedo-like openings, fissures, ridges, looped vessels and fine vessels surrounded by a halo) with the addition of regression structures: focal gray dots/granules.
Late Stage LPLK
Lichen planus-like keratosis in the late phase is characterized by scattered clumps of pigment with diffuse gray dots/granules or gray dots/granules that form what is known as a diffuse granular pattern, and borders that are often scalloped or have a moth-eaten appearance.
In a recent study for the US  LPLKs were compared with non-LPLK cutaneous lesions. LPLKs had the clinical differential diagnosis of basal cell carcinoma, squamous cell carcinoma, neavus, melanoma, seborrehic keratosis, lentigo, and actinic keratosis. Dermoscopic features that were found to distinguish LPLKs from other lesions include: Overall organized dermoscopic structures, scale, orange color, coarse +/- fine granules and peppering as the only feature present. LPLKs were less likely to have moth-eaten borders and irregular dots compared to the other lesions.
- Mehregan: Lentigo senilis and its evolutions. J. Invest. Dermatol. 1975;65:429-33. PMID: 127813.
- Laur et al.: Lichen planus-like keratosis. A clinicohistopathologic correlation. J. Am. Acad. Dermatol. 1981;4:329-36. PMID: 7217401.
- Goldenhersh et al.: Documented evolution of a solar lentigo into a solitary lichen planus-like keratosis. J. Cutan. Pathol. 1986;13:308-11. PMID: 3771875.
- Liopyris et al.: Clinical and dermoscopic features associated with lichen planus-like keratoses that undergo skin biopsy: A single-center, observational study. Australas. J. Dermatol. 2018;. PMID: 30450536. DOI.