What is a prokeratotic lesion?

Porokeratosis: Clinical Features and Management

Porokeratosis is a distinct keratinization disorder characterized by abnormal clonal expansion of keratinocytes, with the pathognomonic histological feature being the cornoid lamella, a thin column of parakeratosis representing the active border of the lesion. 1, 2, 3

Clinical Presentation

Porokeratosis presents with several distinct clinical variants:

• Morphology: Discrete hyperkeratotic papules or plaques surrounded by a threadlike, elevated border that expands centrifugally 3
• Appearance: Lesions typically show:
  • Erythematous, scaly patches or papules
  • Rough, sandpaper-like texture
  • Characteristic peripheral ridge (cornoid lamella clinically)
  • Central brownish discoloration with peripheral "white track" on dermoscopy 3

Common Variants

• Disseminated Superficial Actinic Porokeratosis (DSAP): Most common form, multiple brown annular keratotic lesions on sun-exposed areas 4
• Porokeratosis of Mibelli: Larger, solitary or few plaques with prominent ridge-like borders 3
• Linear Porokeratosis: Following Blaschko's lines
• Other variants: Eruptive bullous, pruriginous, lichen planus-like, and follicular variants 1

Etiopathogenesis

• Genetic basis: Heterozygous mutations in mevalonate pathway enzymes 3
• Triggering factors:
  • Ultraviolet radiation exposure
  • Immunosuppression
  • Systemic diseases
  • Infectious conditions 2

Diagnostic Approach

• Clinical examination: Recognition of characteristic annular lesions with raised borders
• Dermoscopy: Reveals double-marginated white peripheral border - a non-invasive diagnostic tool 3
• Histopathology: Definitive diagnosis through identification of the cornoid lamella - the hallmark feature 1, 3
• Reflectance confocal microscopy: Can aid in diagnosis without biopsy 1

Management Considerations

1. Risk assessment: Evaluate for malignant transformation potential, particularly in:

   • Linear porokeratosis
   • Disseminated superficial actinic porokeratosis
   • Giant lesions 1

2. Treatment options:

   • Topical therapies:

     • Retinoids (tretinoin) - effective for linear porokeratosis 5
     • Vitamin D derivatives (calcipotriol, tacalcitol) - beneficial for disseminated forms 5, 4
     • Imiquimod - particularly effective for Porokeratosis of Mibelli 5
     • 5-fluorouracil 3

   • Systemic therapies:

     • Oral retinoids - useful for extensive or linear forms 5, 3
     • HMGCoA inhibitors - emerging therapy targeting the mevalonate pathway 1

   • Procedural interventions:

     • Cryotherapy
     • Surgical excision
     • Photodynamic therapy 1, 5

3. Preventive measures:

   • Sun protection - critical for DSAP 3
   • Regular follow-up to monitor for malignant transformation 3

Malignancy Risk

Porokeratosis is considered a premalignant condition with potential for transformation to:

• Squamous cell carcinoma
• Basal cell carcinoma
• Bowen's disease
• Rarely, melanoma 1, 2

Treatment Challenges

Treatment response is often unsatisfactory and variable between different clinical variants. The choice of therapy should be guided by:

• Variant type
• Extent of disease
• Location of lesions
• Patient factors including comorbidities 5

Long-term follow-up is essential due to the chronic nature of the condition and malignancy risk 2, 3.