Key Insights On Treating Plantar Psoriasis
Topical corticosteroids have three useful mechanisms of action. First, they are potent cutaneous vasoconstrictors that slow epidermal proliferation. Secondly, they are strong immune blockers of this T-cell mediated disease. Finally, corticosteroids are anti-inflammatory by slowing lymphocyte and cytokine mediators. Initially, patients can use a class I steroid like halobetasol (Ultravate) for a maximum of two weeks with a class III mid-potency ointment such as triamcinolone (Kenalog, Bristol-Myers Squibb)after initial improvement.
Hydration of the skin before application increases corticosteroid absorption fivefold while plastic wrap occlusion increases hydration 40 percent and increases corticosteroid efficacy up to 100-fold.5 The optimal frequency of application is two to three times per day. Patients can significantly reduce the risk of adverse drug reactions such as tachyphylaxis, atrophy and striae by suspending applications one day per week.5 Patients should avoid systemic steroids because a severe rebound reaction often occurs upon cessation.
Coal tars inhibit DNA synthesis. Coal tar 5% applications transiently trigger hyperplasia but after 40 days of application reduce epidermal thickness by 20 percent.5 Salicylic acid ointment or gels are keratolytic at 3 to 6% concentrations. They help thin the hyperkeratotic plaques by solubilizing intercellular cement and enhancing desquamation. Urea compounds have a softening and hydrating effect at lower concentrations, and are keratolytic at higher concentrations. They work by disrupting hydrogen bonds within epidermal proteins. Calcipotriene is a vitamin D3 analogue that induces terminal epidermal differentiation and inhibits keratinocytes production. The efficacy of calcipotriene matches class II topical steroids without their adverse effects.5
It is useful to remember that combinations of these agents can synergistically potentiate each other’s actions. Some effective products exploit this effect by combining calcipotriene (Dovonex, Warner Chilcott) with a potent corticosteroid. Phototherapy combining oral retinoids with PUVA or UVB administered with special light boxes for the soles and palms can be effective.
Psoriasis typically follows a chronic and recurrent course. Patients with generalized involvement are best served by dermatology consultation. In addition to phototherapy, dermatologists can employ oral immunosuppressive therapies like acitretin (Soriatane, Stiefel Laboratories), methotrexate (Trexall) and cyclosporines. Methotrexate with folic acid supplementation can clear many cases of palm and sole psoriasis within four to six weeks.
A topical retinoid, tazarotene (Tazorac, Allergan), modulates differentiation and proliferation of epithelial tissue, and perhaps has anti-inflammatory and immunomodulatory activities. There are several protocols but the least irritating is to apply the medication for 15 to 20 minutes and then wash it off. Topical retinoids are effective but childbearing females must avoid them because the retinoids are teratogenic and carry a class X warning.6
New biologic therapies like etanercept (Enbrel, Amgen) and tumor necrosis factors are available for severe unresponsive psoriasis and may be tertiary care choices. Richetta and coworkers found that adalimumab (Humira, AbbVie) for 12 weeks was safe and efficacious in an open-label clinical trial of patients with palmoplantar psoriasis.7