Prescribe topical therapy for psoriasis safely and appropriately
Most patients with psoriasis use topical treatment of one form or other. As with all topical treatments, a range of products may be required depending on the site, severity and chronicity of the skin disease.
Emollients relieve dryness, fissuring and irritation. Thick ointments based on white soft paraffin, beeswax or lanolin are recommended for chronic plaques especially on hands and feet. Keratolytics such as salicylic acid (0.5%-10%) and / or urea (5-40%) reduce scaling and may be incorporated in shampoos, lotions, creams, ointments and pastes. Salicylism is a potential risk of extensive use of high concentration topical salicylic acid. Both salicylic acid and urea may irritate and cause transient stinging especially if the treated skin is fissured, excoriated or eroded.
Calcipotriol is a derivative of calcitriol (1,25-dihydroxy cholecalciferol or active vitamin D). Calcipotriol is available as an ointment, cream and scalp solution at a concentration of 50µg/g and is applied to psoriasis plaques twice daily to reduce scaling and induration. Erythema often persists despite continued treatment.
Topical calcipotriol can be used safely long term. It is generally well tolerated, but sometimes causes stinging and / or irritant dermatitis, especially on the face.
Calcipotriol is inactivated by salicylic acid. If more than one 100g-tube is used each week, calcium levels in blood and urine should be monitored. Calcipotriol is very poisonous to dogs.
Topical corticosteroids are popular with patients because they are clean, well tolerated and easy to apply. However, they are not ideal long term because of tachyphylaxis and adverse effects. Potent or ultrapotent topical steroids may significantly improve the appearance of psoriasis, but they do not result in remission. They may be usefully combined with other topicals including calcipotriol, salicyclic acid, antifungal agents.
The patient illustrated has psoriasis. He has been applying clobetasol propionate ointment (an ultrapotent topical steroid) and has used about 100g each week for several months. He is also taking oral prednisone because of severe psoriatic arthropathy. He has developed severe striae and marked generalised cutaneous atrophy. Note the transparency of abdominal skin and Cushingoid habitus. His psoriasis was subsequently extremely difficult to control and he suffered several serious complications of steroid therapy.
Coal tar continues to be prescribed for patients with psoriasis and eczema. It is anti-inflammatory i.e. it reduces redness and itching. Pine tar and ichthammol preparations are also available.
Hospitalised patients with chronic plaque psoriasis may be prescribed 2-5% crude coal tar in an emollient base under dressings, preceded by daily exposure to ultraviolet radiation (Goeckerman regime). Crude coal tar is black, malodorous, messy and rarely used nowadays.
There are several over-the-counter and prescription products containing more cosmetically acceptable refined or liquified coal tar (liquor picis carbonis), often combined with salicylic acid as a descaling agent and/or sulphur, resorcinol and other traditional anti-inflammatory agents. They are most useful for scalp psoriasis and seborrhoeic dermatitis, applied for an hour or more before washing out with a shampoo also containing tar and salicylic acid.
Dithranol, also known as anthralin, is one of the most effective preparations available for treating psoriasis especially applied twice daily in Lassar’s paste (zinc, salicylic acid and paraffin) under tube gauze dressings. It may be preceded by a tar bath and exposure to ultraviolet radiation (Ingram regime).
Dithranol causes severe irritation on normal skin and stains skin and clothing a purple-brown colour (it wears off the skin within about ten days but leaves permanent marks on fabric). For outpatients, dithranol in a cream base is left on the skin for only 10 to 30 minutes. This 'short contact' method reduces burning and staining.