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Psoriasis afflicts 1-3% of the general population1,2 and affects the scalp in about 40% of those suffering from the disease.3 In some patients, the scalp is the only site affected.4 In long-standing scalp psoriasis, hair thinning does occur.5 For the patient, scalp psoriasis is itchy and uncomfortable, and cosmetically disturbing because of shedding of scales. It is difficult to manage6 because treatment is unpleasant, generally produces indifferent results, only partial control and relapse rates are high.5 Patient compliance is often poor as currently available medications are often greasy, sticky, odorous, can cause changes in hair color, are difficult to apply, require frequent application, and are expensive.
Psoriasis of the scalp is often a therapeutic challenge. Topical treatment is the favourite treatment approach systemic treatment is not as effective.7 The vehicles for topical scalp preparations are usually clear gels or lotions suitable for easy application and subsequent removal by the patient.8
Tar preparations are disagreeable to use, and both coal tar and anthralin preparations stain. Crude coal tar (2-5%), with 5-10% salicylic acid incorporated in petrolatum, is very messy, but can be useful for treating in-patients recalcitrant psoriasis. Purified tar preparations are more suitable for treating out-patients. Note that some patients may require treatment each week for up to two months. Shampoos containing coal tar can be used by patients as frequently as necessary. Anthralin causes skin irritation and great care must be taken to avoid contact with the eyes.8
The carcinogenicity of coal tar has clearly been demonstrated by in vitro and animal studies, and appears to be potentiated by concomitant use of ultraviolet radiation. Systemic absorption of mutagens from topically applied tar has been demonstrated in humans. Conclusive evidence for the carcinogenicity of tar used in dermatologic practice is lacking,9 and will only be provided by cohort studies involving several thousand patients. Our lead article in the very first issue of this Letter was entitled, "Should coal tar preparations be widely available without prescriptions.?"10
Various potent topical formulations (i.e. solutions or creams) of corticosteroids are used to treat scalp psoriasis. Prolonged use can cause the usual, well-recognized problems. Once the patient has improved, treatment should be tapered gradually to reduce the chance of relapse.
In a multi-centre, prospective randomized, double-blind, parallel group study in 49 adults, calcipotriol (50 mcg/ml) was well tolerated and significantly superior to its own vehicle used as placebo in reducing redness, thickness, scaliness, and extent of psoriasis.6 In another study, betamethasone 17-valerate solution (1 mg/ml) was significantly more effective than calcipotriol (50 mcg/ml) and was associated with statistically significant less local irritation on the scalp and face.12
In severe, recalcitrant scalp psoriasis, it may be necessary to consider systemic therapy with acitretin or methotrexate8 combined with topical corticosteroids or vitamin D3 preparations.7 Unfortunately, hair acts as an ultraviolet shield; hence for scalp psoriasis, PUVA therapy is only useful in patients who are significantly bald.8 Grenz ray (soft x-rays) therapy has been found to be effective,13 but this form of therapy is considered to have unacceptable risks and is no longer used in most countries.
When scaling is thick and adherent, it must be removed by overnight application of a keratolytic. Dr. Kenneth Arndt uses a phenol/saline lotion (P&S liquid).11 Professor Gollnick uses salicylic acid (up to 15%) oil formulations, applied for 12-24 hours under occlusion.7 Professor Kragballe prescribes a daily application of 5% tar and 5% salicylic acid in petrolatum.14 The scalp should be shampooed daily. Once the crust/scale is removed, the keratolytic can be used as necessary to keep the scalp reasonably free from scaling. After shampooing, an appropriate potent corticosteroid formulation should be massaged into the scalp. Dr. Arndt uses clobetasol scalp solution or cream. In order to achieve and maintain a good response, he often finds it necessary to use combination therapy and to substitute topical anthralin or calcipotriene for the corticosteroid.11 If appropriate, other options such as tar preparations or the milder topical corticosteroids can be substituted.7
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