Diffuse Epidermolytic Palmoplantar Keratoderma (Unna–Thost disease)
- Most common type of diffuse keratoderma
- Associated with keratin 1 and 9 gene mutations
- Keratin 9 only expressed in suprabasal layers
- Keratin 1 and 10 gene mutations associated with epidermolytic ichthyosis
- Keratin 1 gene mutations associated with focal palmoplantar keratoderma
- Keratin 9 gene mutations disrupt keratin filament association, promoting cell lysis and tonofilament aggregation
- Palmoplantar skin progresses from red to yellow with hyperkeratosis by age 3-4 years
- Confluent hyperkeratosis with sharply defined waxy erythematous borders by adulthood
- Dorsal-sparing
- Possible knuckle pads, thickened nails
- Rare blistering and fissuring (childhood or later secondary to oral retinoid use)
- Severe pain with Tonotubular variant
- Transgredient lesions with Greither variant
Pathology:
- Epidermolytic hyperkeratosis (vacuolated suprabasal keratinocytes)
- May also see coarse keratohyalin granules, acanthosis, orthohyperkeratosis
- Multiple biopsies usually required before a diagnosis can be made
Differential:
- Epidermolytic ichthyosis
- Non-epidermolytic palmoplantar keratoderma
- Mechanical debridement
- Topical keratolytic to prevent fissures (50% propylene glycol, lactic acid, urea, 4-6% salicylic acid)
- Oral retinoids (risk of significant peeling and compromise of volar skin)
- Topical calcipotriene