Palmoplantar Psoriasis

Palmoplantar psoriasis is psoriasis that is confined to or dominant on the palms and soles, with well demarcated, thick, scaly, fissured plaques. It may be hyperkeratotic or accompanied by sterile pustules.

It accounts for around 3 to 4% of people with psoriasis and is more frequent in adults, with a female predominance in the pustular form. It causes marked disability from pain, fissuring and loss of grip and gait.

Triggers include friction and trauma, smoking, infection, stress, drugs (lithium, beta blockers, antimalarials) and metal allergy in some. Smoking is strongly associated, particularly with palmoplantar pustular disease.

Pathophysiology.

Psoriatic inflammation is driven by interleukin-23 and interleukin-17, with amplification by mechanical stress on acral skin. The thick palmoplantar stratum corneum retains scale and impedes drug penetration, which explains the poor response to topical therapy.

• Sharply demarcated, erythematous, thickened plaques with adherent scale on the palms and soles, often with painful fissures.
• Pustular form: sterile yellow brown pustules on the thenar and hypothenar eminences, arches and heels.
• Nail pitting, onycholysis and subungual hyperkeratosis in many. Psoriasis at other sites in some.
• Pain, impaired hand and foot function, and bleeding fissures.

Red flags.

• Asymmetrical disease, which suggests tinea, contact dermatitis or malignancy.
• Fever with spreading erythema (secondary infection).
• Joint pain or swelling, suggesting psoriatic arthritis.

• Clinical diagnosis with examination of the nails, scalp and skin folds for psoriasis at other sites.
• Fungal scraping for potassium hydroxide microscopy and culture to exclude tinea.
• Patch testing if allergic contact dermatitis is suspected. Swab for bacteria if crusting or purulent.
• Skin biopsy if the diagnosis is unclear.
• Screening for psoriatic arthritis (symptoms of joint pain, stiffness and dactylitis).

Differential diagnosis. Hand and foot eczema, tinea pedis or manuum, inherited and acquired palmoplantar keratoderma, pityriasis rubra pilaris, lichen planus, secondary syphilis, contact dermatitis and acrodermatitis continua.

Topical.

• Very potent corticosteroid (clobetasol propionate 0.05%) once daily for up to 4 weeks, with occlusion at night, then step down to twice weekly.
• Keratolytics: salicylic acid 5 to 10% in white soft paraffin, or urea 20 to 40%, to descale before steroid application.
• Calcipotriol 50 micrograms/g or its combination with betamethasone once daily, and coal tar preparations.

Phototherapy and systemic treatment.

• Hand and foot phototherapy with psoralen and ultraviolet A (soak or topical) or narrowband ultraviolet B two to three times weekly. Combination with acitretin improves response.
• Acitretin 25 to 50 mg daily, especially for hyperkeratotic disease. It is teratogenic, requires strict contraception during treatment and for 3 years after stopping, and needs lipid and liver monitoring.
• Methotrexate 7.5 to 15 mg once weekly (maximum 25 mg) with folic acid 5 mg weekly, or ciclosporin 2.5 to 5 mg/kg/day in two divided doses.
• Apremilast 30 mg twice daily after a 5 day titration.
• Biologics for severe disease: secukinumab 300 mg at weeks 0 to 4 then every 4 weeks, ixekizumab, guselkumab 100 mg at weeks 0 and 4 then every 8 weeks, or risankizumab 150 mg at weeks 0 and 4 then every 12 weeks. Screen for tuberculosis, hepatitis B, hepatitis C and HIV first.
• Smoking cessation, glove use and avoidance of trauma.

Monitoring. Review at 4 weeks and 12 weeks, with pain, function and extent. Monitor drug toxicity with the tests for each agent.

Referral and escalation. Refer to dermatology for resistant disease, diagnostic doubt or need for phototherapy or systemic treatment.

Special groups. Acitretin and methotrexate are contraindicated in pregnancy. Use ciclosporin or certolizumab with specialist input.