Ultraviolet radiation helps many patients with psoriasis , perhaps by increasing the production of cholecalciferol in the skin. Calcipotriol and tacacitol are analogues of chlolecalciferol, which do not cause hypercalcaemia and calciuria when used topically in the recommended dose. Both can be used for mild to moderate psoriasis affecting less than 40% of the skin. They work by influencing vitamin D receptors in keratinocytes, reducing epidermal pro-liferation and restoring a normal horny layer. They also inhibit the synthesis of polyamines.
Patients like calcipotriol because it is odourless, colour-less and does not stain. It seldom clears plaques of psoriasis completely, but does reduce their scaling and thickness. Local and usually transient irritation may occur with the recommended twice-daily application. One way of lessening this is to combine the use of calcipotriol with that of a moderately potent steroid, the calcipotriol being applied in the evening and the steroid in the morning (see Topical corticosteroids below). Calcipotriol should not be used on the face. Up to 100 g/week calcipotriol may be used but the manufacturer’s recommendations should be con-sulted when it is used in children over 6 years old.
Our current practice, which may be unnecessary, is still to check the blood calcium and phosphate levels every 6 months, especially if the psoriasis is widespread or the patient has had calcified renal stones in the past.
Tacalcitol ointment (not available in the USA) is applied sparingly once daily at bedtime, the maximum amount being 10 g/day. As with calcipotriol, irritation aoften transientamay occur. The drug should not be used for longer than a year at a time and is not yet recommended for children.
Tazarotene is a topically active retinoid. It has a selective affinity for RARs and, when bound to these, improves psoriasis by reducing keratinocyte prolifera-tion, normalizing the disturbed differentiation and lessening the infiltrate of dermal inflammatory cells. It is recommended for chronic stable plaque psoriasis on the trunk and limbs covering up to 20% of the body. It is applied sparingly once a day, in the evening, and can be used for courses of up to 12 weeks. It seldom clears psoriasis but reduces the induration, scaling and redness of plaques. It is available as either a 0.05% or 0.1% gel. Like the vitamin D analogues, its main side-effect is irritation. If this occurs, the strength should be reduced to 0.05%; if irritation persists, applications should be cut to alternate days and a combination treatment with a local steroid considered.
In the USA, tazarotene is licensed for children aged 12 years and over; in Europe it is currently licensed only for adults over 18 years old. The drug should not be used in pregnancy or during lactation. Females of childbearing age should use adequate contraception during therapy.
Practice varies from centre to centre and from country to country. Many dermatologists, particularly in the USA, find topical corticosteroids most helpful and use them as the mainstay of their long-term management of stable plaque psoriasis. Patients like them because they are clean and reduce scaling and redness.
In our view such usage is safe, but only under proper supervision by doctors well aware of problems such as dermal atrophy, tachyphylaxis, early relapses, the occasional precipitation of unstable psoriasis (Fig. 5.16) and, rarely, in extensive cases, of adrenal suppression caused by systemic absorption. A commitment by the prescriber to keep the patient under regular clinical review is especially important if more than 50 g/week of a moderately potent topical corticosteroid prepara-tion is being used. Combined tar–steroid preparations may also be helpful (Formulary 1).
The regular use of topical corticosteroids is less controversial under the following circumstances.
1 In ‘limited choice’ areas such as the face, ears, gen-itals and flexures where tar and dithranol are seldom tolerated (mildly potent steroid preparations should be used if possible).
2 For patients who cannot use vitamin D analogues,tar or dithranol because of allergic or irritant reac-tions (moderately potent preparations, except for ‘no choice’ areas where mildly potent ones should be used if possible).
3 For unresponsive psoriasis on the scalp, palms and soles (moderately potent, potent and very potentabut only in the short termapreparations).
4 For patients with minor localized psoriasis (moder-ately potent or potent preparations).
A combination ointment of calcipotriol and beta-methasone diproprionate (a potent corticosteroid) has recently been marketed in the UK. The maximum dose should not exceed 15g/day or 100g/week and the ointment should not be applied for longer than 4 weeks.
Dithranol is rarely used in the USA nowadays but remains popular in the UK. Like coal tar it inhibits DNA synthesis, but some of its benefits may be brought about by the formation of free radicals of oxygen.
Dithranol is more tricky to use than coal tar. It has to be applied carefully, to the plaques only; and, if left on for more than 30 min, must be covered with gauze dressings. It is irritant, so treatment should start with a weak (0.1%) preparation, thereafter the strength can be stepped up at weekly intervals. Dithranol stronger than 1% is seldom necessary. Irritation of the sur-rounding skin can be lessened by the application of a protective bland paste, e.g. zinc paste.
Dithranol stains normal skin, but the purple-brown discoloration peels off after a few days. It also stains bathtubs, clothesaand anything else it touches. One popular regimen is to apply dithranol daily for 5 days in the week; after 1 month many patients will be clear.
Short contact therapy, in which dithranol is applied for no longer than 30 min, is also effective. Initially a test patch of psoriasis is treated with a 0.1% dithranol cream, left on for 20 min and then washed off. If there is no undue reaction, the application can be extended the next day and, if tolerated, can be left on for 30 min. After the cream is washed off, a bland application such as soft white paraffin or emulsifying ointment is applied. Depending on response, the strength of the dithranol can be increased from 0.1 to 2% over 2–3 weeks. Suitable preparations are listed in Formulary 1.
Dithranol is too irritant to apply to the face, the inner thighs, genital region or skin folds. Special care must be taken to avoid contact with the eyes. Recent research has shown that applying triethanolamine after the dithranol has been removed reduces inflam-mation and staining without diminishing the thera-peutic effect. Crude coal tar and its distillation products have been used to treat psoriasis for many years. Their precise mode of action is uncertain but tar does inhibit DNA synthesis.
Many preparations are available but it is wise to become familiar with a few. The less refined tars are smelly, messy and stain clothes, but are more effective than the cleaner refined preparations. Tar emulsions can also be added to the bath. Suitable preparations are listed in Formulary 1. Surprisingly, no increase in skin cancer has been found in patients treated for long periods with tar preparations; it has even been suggested that psoriatics are less likely than normal to develop skin cancer.