Lichen planus-like keratosis (BLK)
Benign lichenoid keratosis (BLK); lichenoid keratosis; solitary lichen planus; LPLK
Lichen planus-like keratosis is a common solitary inflamed regressing seborrhoeic keratosis or solar lentigo that mimics a malignant lesion both clinically and histologically. Most lesions present in middle-aged to older adults as a single pink-violaceous or red-brown papule or thin plaque on the trunk or upper limbs, with itch, mild scale or crusting. Histologically the lichenoid infiltrate masquerades as actinic keratosis, Bowen's disease, lentigo maligna or even superficial BCC — the diagnosis is almost always made by histology after a biopsy taken for diagnostic uncertainty. Recognition matters because once labelled, no further treatment is required and the patient avoids unnecessary excision.
Clinical features
- Solitary pink, red-brown, violaceous or grey papule or thin plaque, 5–20 mm.
- Distribution — upper chest, back, shoulders, dorsal forearms, neck — overlapping with sun-damaged sites.
- Mild itch, irritation, occasional crust or fine scale.
- Median age 50–70; female predominance in some series.
- Usually evolves over weeks to months and may resolve spontaneously over a year.
Dermoscopy
- Diffuse granular ("annular-granular") pattern of brown-grey dots, often arranged in clusters, reflecting regressing melanin and lichenoid infiltrate.
- Background pink-brown with patchy structureless areas; remnants of a reticular pigment network may be visible.
- Important overlap with lentigo maligna (which also shows annular-granular structures in regression) and with regression in melanoma — biopsy is the safer default.
Histology
- Lichenoid band-like lymphocytic infiltrate at the dermoepidermal junction with vacuolar interface change and apoptotic keratinocytes.
- Often within a residual solar lentigo or seborrhoeic keratosis with focal preserved architecture at the periphery — a key diagnostic clue.
- Pigment incontinence, dermal melanophages.
- Differential on histology — actinic keratosis with lichenoid features, Bowen's disease with regression, lichen planus, fixed drug eruption, lentigo maligna with regression.
Clinical differential
- Actinic keratosis — drier, gritty, multiple, in chronically sun-damaged skin.
- Bowen's disease — well-demarcated scaly red plaque, often larger.
- Superficial BCC — pearly border, fine telangiectasias, slow growth over years.
- Lentigo maligna — slow-growing macular pigmentation on chronically sun-damaged skin; biopsy if any pigment irregularity.
- Fixed drug eruption, psoriasis, eczema.
Management
- Biopsy is the rule — diagnosis is rarely made clinically with confidence.
- After histological diagnosis: reassurance, no further treatment required.
- Lesions typically resolve spontaneously over months.
- Cosmetic concern — topical mid-potency steroid or curettage if symptomatic; recurrence in the same site is rare.
References
- Morgan MB et al. Benign lichenoid keratosis — a clinicopathologic reappraisal. J Cutan Pathol; 2005.
- Bowen AR et al. Lichenoid keratosis vs lichen planus — distinguishing features. Am J Dermatopathol; 2017.
- Argenziano G, Zalaudek I. Dermoscopy of benign lichenoid keratosis. Br J Dermatol; 2013.
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