Clinically, lichenoid keratosis may simulate an actinic keratosis, basal cell carcinoma (eg, nodular or superficial), squamous cell carcinoma in situ, seborrheic keratosis, or a pigmented or amelanotic melanoma, whereas histologically it is almost identical to lichen planus.
The pathogenesis of lichenoid keratosis is not entirely understood, but it is thought to represent an inflammatory reaction occurring in a preexisting solar lentigo, seborrheic keratosis, or actinic keratosis.
Lichenoid keratoses are usually asymptomatic but may be slightly pruritic. Patients occasionally report that the lesion has changed, prompting examination of the lesion and biopsy. On average, the lesion has been present for 6 months at the time of diagnosis.
Most lichenoid keratoses are erythematous / pink, although some are violaceous or hyperpigmented. They are typically solitary and range in size from 3-19 mm in diameter. They may be scaly, pearly, or indurated.
Lichenoid keratoses often involute spontaneously over a period of months.
L43.9 – Lichen planus, unspecified
403198004 – Lichenoid actinic keratosis
Differential Diagnosis & Pitfalls
- Lichenoid actinic keratosis
- Lichen planus – Presents with multiple pruritic, polygonal purple plaques, whereas lesions of lichenoid keratosis are usually solitary. Look for Wickham striae and oral white lacy reticulate plaques on buccal mucosa (see oral lichen planus).
- Basal cell carcinoma – Nodular subtype presents with a solitary shiny, red nodule with large telangiectatic vessels that may show ulceration or bleeding; superficial subtype presents with flat, well-demarcated erythematous plaques resembling eczema but unresponsive to eczema therapies. Biopsy is diagnostic.
- Squamous cell carcinoma – A verrucous, scaly, often crusted papule or plaque. Biopsy is diagnostic.
- Seborrheic keratosis – A hyperpigmented, "stuck-on"-appearing plaque with horn cysts not confined to arms, chest, head, and neck; usually multiple. Biopsy will show pseudohorn cysts.
- Nevus – A skin-colored to hyperpigmented macule or papule that is usually not scaly. Biopsy is diagnostic.
- Melanoma – Usually presents with irregularities in pigmentation, colors, borders, and symmetry. Biopsy is diagnostic.