Palmoplantar Keratoderma (PPK)
Thickened skin on palms and soles — what it is, how it relates to ichthyosis, and how it's managed.
What is Palmoplantar Keratoderma?
Palmoplantar Keratoderma (PPK) is a group of inherited skin conditions characterised by hyperkeratosis — abnormal thickening of the skin — specifically on the palms of the hands and soles of the feet.
How PPK Relates to Ichthyosis
PPK as a feature within ichthyosis
Many ichthyosis types include PPK as part of their presentation. Lamellar Ichthyosis typically causes thickened and fissured soles. Ichthyosis Vulgaris has mild PPK in some individuals. Some forms of KID Syndrome have severe palmoplantar hyperkeratosis. This is not a separate condition — it's a feature of the underlying gene mutation.
Shared genes between PPK and ichthyosis
Some genes cause PPK without ichthyosis (KRT9, which is expressed only in palmoplantar skin). Others — like FLG — cause both ichthyosis vulgaris and palmoplantar keratoderma. Genes such as TGM1 cause lamellar ichthyosis where palmoplantar thickening is part of the broader ichthyotic phenotype rather than a distinct PPK entity. This gene-phenotype relationship is why PPK and ichthyoses are classified together under the EDD framework — they share molecular pathways even when their clinical appearance differs.
PPK-syndrome overlap conditions
Several syndromes combine PPK with additional systemic features and are closely related to ichthyosis. Mal de Meleda (SLURP1 mutation) has PPK plus constriction bands. Papillon-Lefèvre Syndrome (CTSC mutation) has PPK plus severe gum disease. These are classified under EDD alongside ichthyosis types.
Main Types of PPK
Epidermolytic PPK (Vörner type)
The most common form of hereditary PPK. Keratin 9 is expressed exclusively in palmoplantar skin, explaining why other body areas are unaffected. Presents as well-demarcated, yellow-white, thickened plaques on the entire surface of palms and soles. Epidermolytic histology (blistering at the cellular level) distinguishes it from the Unna-Thost type. Often associated with hyperhidrosis and odour.
Diffuse PPK — KRT1 type
Diffuse thickening over palms and soles caused by mutations in KRT1 (keratin 1). Clinically similar to Vörner type. Note: the old "Unna-Thost" eponym for this entity has been revised — re-examination of the original Thost family found epidermolytic changes on biopsy, and the non-epidermolytic/epidermolytic distinction for KRT1 mutations is no longer considered reliable without histology. KRT1 is expressed more widely than KRT9, so mild scaling may extend beyond the palms and soles in some individuals. Hyperhidrosis is common.
Focal PPK
Thickening is limited to pressure points and areas of repeated trauma — tips of fingers and toes, central palm, plantar pressure points. Often presents in early childhood once walking begins. Isolated focal PPK is primarily caused by KRT6C and KRT16 mutations. When nail involvement is also present, this overlaps with Pachyonychia Congenita (PC), which can be caused by mutations in KRT6A, KRT6B, KRT6C, KRT16, or KRT17. Painful plantar lesions can significantly impact mobility.
Punctate PPK
Characterised by small, discrete, keratotic papules (bumps) rather than diffuse thickening. Multiple genetic causes. Can appear during adolescence or early adulthood. Lesions may cause discomfort when walking. Distinct from the diffuse forms — often misdiagnosed initially as warts or calluses.
Mal de Meleda (Transgrediens PPK)
A severe form where thickening extends beyond the palms and soles onto the dorsal hands, feet, and wrists (transgrediens). SLURP1 encodes a protein involved in cholinergic signalling in skin. Associated with constricting bands around digits (pseudo-ainhum), hyperhidrosis, and strong odour. Autosomal recessive — both copies of the gene must be mutated. Related to ichthyosis under EDD.
Papillon-Lefèvre Syndrome
PPK combined with severe early-onset periodontitis (gum and supporting bone destruction). CTSC encodes cathepsin C, a protease important in immune function. Children lose their primary (milk) teeth early; permanent teeth may also be lost without treatment. Dermatology and dental management must be coordinated. Increased susceptibility to bacterial infections.
Symptoms Common to PPK Types
Management of PPK
Management follows the same keratolytic principles as ichthyosis management, with additional focus on the mechanical removal of thick plantar skin:
Keratolytic Agents
- Urea 25–40% — breaks down protein bonds in thick skin. Higher concentrations (40%) suitable for sole thickening. Apply after soaking.
- Salicylic acid 6–10% — softens and lifts scale. Can be used in combination with urea.
- Lactic acid 10–12% — gentler option for palms. Available OTC in many emollient products.
- Propylene glycol — enhances penetration of other keratolytics when used in combination.
Mechanical Removal
- Foot soaking — 20–30 minutes in warm water before mechanical removal. Essential to soften scale first.
- Pumice stone — gentle circular motion on softened skin immediately after soaking. Never use on dry skin.
- Emery board / foot file — fine abrasive tools for less severe thickening. Replace regularly.
- Podiatry — professional blade removal for severe plantar thickening. Available on NHS referral.
For Hyperhidrosis
- Aluminium chloride 20% — antiperspirant solution (e.g. Anhydrol Forte). Apply to dry palms/soles at night. Very effective for hyperhidrosis reduction.
- Iontophoresis — electrical current therapy for palmar/plantar hyperhidrosis. Available at some NHS dermatology units.
- Botulinum toxin (Botox) — highly effective for severe palmar/plantar hyperhidrosis. NHS prescribable for significant functional impairment.
- Antibacterial wash — chlorhexidine or tea tree washes reduce bacterial colonisation contributing to odour.
Systemic Treatments
- Acitretin (oral retinoid) — most effective systemic option for severe PPK. Reduces scale production. Long-term use requires monitoring (liver, lipids). Not suitable in pregnancy.
- Alitretinoin — licensed for severe chronic hand eczema; sometimes used off-label in palmar PPK. Fewer teratogenicity concerns than acitretin.
- Low-dose retinoids — some dermatologists use low-dose isotretinoin off-label. Discuss with your dermatologist.
Footwear & Daily Life
- Wide-fit shoes with cushioned insoles reduce plantar pressure and discomfort.
- Moisture-wicking socks reduce maceration — avoid cotton (holds moisture). Wool or synthetic technical fabrics preferred.
- Gel heel cups or custom orthotics for focal heel thickening.
- Avoid walking barefoot on rough surfaces — risk of fissuring.
- Swimming helps — the prolonged water exposure softens plantar scale.
Pain Management
- Padded dressings (Mepilex, Compeed) over fissures — protects while healing. Change daily.
- Tissue glue (Dermabond / superglue) into clean fissures — seals the split to allow healing and reduces pain.
- Topical lidocaine for temporary relief of painful plantar lesions before walking.
- Refer to pain clinic if persistent neuropathic pain develops.