Porokeratosis
Includes DSAP (commonest), porokeratosis of Mibelli, linear porokeratosis, punctate porokeratosis, porokeratosis palmaris et plantaris disseminata
Porokeratosis is a heterogeneous group of disorders of keratinisation defined histologically by the cornoid lamella — a column of parakeratotic cells overlying a focus of dyskeratosis. Lesions present clinically as annular plaques with a distinctive raised, hyperkeratotic border and an atrophic centre. Most subtypes are inherited mevalonate-pathway disorders (MVK, MVD, FDPS, PMVK germline / mosaic mutations). The malignant transformation rate to squamous cell carcinoma, Bowen's disease or BCC ranges from 7% to over 30%, depending on subtype, lesion size, duration and immunosuppression — making porokeratosis a clinically important pre-malignant condition that warrants surveillance and active treatment of high-risk lesions.
Subtypes
- Disseminated superficial actinic porokeratosis (DSAP) — commonest; multiple small (3–10 mm) annular hyperkeratotic plaques on sun-exposed extremities; onset in 3rd–5th decade; UV exacerbates. SCC risk low (commonly <3%).
- Porokeratosis of Mibelli — solitary or few large (cm-scale) plaques on extremities, in childhood / young adult onset; higher SCC risk (~20%).
- Linear porokeratosis — Blaschkoid distribution along an extremity, mosaic; onset in childhood; highest SCC risk (~20–30% lifetime).
- Porokeratosis palmaris et plantaris disseminata — palms/soles ± diffuse trunk lesions.
- Punctate porokeratosis — multiple tiny (1–2 mm) keratotic papules on palms/soles.
Clinical features
- Annular plaques with a raised, hyperkeratotic peripheral ridge ("cornoid lamella" in cross-section) and central atrophy.
- Asymptomatic or mildly pruritic; cosmetic concern is the usual presenting complaint for DSAP.
- Risk factors for malignant transformation: large lesion (>3 cm), long duration, linear or genital sites, immunosuppression (especially organ transplant recipients), prior radiation.
- Warning signs of malignant transformation: ulceration, induration, pain, bleeding, rapid growth — biopsy any change.
Histology
- Cornoid lamella — the defining feature: a thin column of parakeratosis overlying a focus of dyskeratosis and absent granular layer.
- Surrounding epidermis often atrophic; mild perivascular lymphocytic infiltrate beneath.
- In long-standing lesions: full-thickness atypia (Bowen's), invasive SCC, or BCC.
- Multiple sections through the suspected ridge may be needed to capture the cornoid lamella.
Management
- UV protection — daily broad-spectrum SPF 50+, sun-protective clothing.
- Cosmetic / symptomatic treatment for DSAP:
- Topical 5-FU, imiquimod, retinoids (tretinoin), diclofenac gel.
- Photodynamic therapy.
- Cryotherapy for individual lesions.
- Topical or oral statins (lovastatin) — emerging therapy targeting the underlying mevalonate pathway defect; promising data in DSAP.
- For larger / long-standing / linear lesions:
- Active treatment with field therapy or PDT, or surgical excision of high-risk areas.
- Excision and complete histology of any suspicious change.
- Mohs micrographic surgery for SCC arising in porokeratosis (often margins difficult to define).
- In organ transplant recipients — prioritise low threshold for treatment given accelerated transformation risk.
Surveillance
- Annual full skin examination.
- More frequent for high-risk subtypes (linear, large Mibelli) and OTRs.
- Patient education to self-monitor and present early with any change in established lesions.
References
- Sertznig P et al. Porokeratosis — present concepts. J Eur Acad Dermatol Venereol; 2012.
- Atzmony L et al. Topical statins for the treatment of disseminated superficial actinic porokeratosis. JAMA Dermatol; 2020.
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