Dithranol has been used for over 50 years in the treatment of stable plaque psoriasis and remains an effective, inexpensive and extensively used topical remedy, without long term local, systemic or teratogenic effects.
Efficacy
Treatment is designed to limit dithranol application to the affected skin by applying dithranol (0.1-2%) in a non-smudging zinc oxide (Lassar's) paste. This is applied to each plaque by a trained nurse or tutored patient and, after covering with powder and Stockinette to reduce smearing, left on for up to 24 hours. Treatment is frequently combined with UVB phototherapy and a tar bath (the Ingram regimen). Patients with plaque psoriasis respond after approximately 20 days of treatment, and relapse at a rate of 10% per month.
Because of the difficulty in its application, this type of dithranol treatment is normally carried out under hospital supervision. Cream or ointment based preparations may smudge onto and, hence, burn, surrounding unaffected skin when used as overnight applications. Application of high concentrations of dithranol (1-10%) for 15-30 minutes daily (short contact therapy), followed by wash-off, allows sufficient dithranol to remain fixed to the plaques for a clinical effect to be obtained without the need for special dressings, as there is less risk of smudging of dithranol onto peri-lesional skin. Skin irritancy may still occur when dithranol is smeared on normal skin during wash-off.
Patients require a careful explanation or, ideally, a demonstration of the technique. Preparations such as dithrocream are available in multiple concentrations. Normally treatment is started at a lower concentration with each course of treatment and gradually increased within the patient’s tolerance, reducing the strength if there is burning and increasing it where possible. Response can be gauged by palpating the plaque. Once lesions are palpably flat dithranol should be discontinued.
Safety, side-effects and patient acceptability
The immediate unwanted effects of skin staining and irritancy, however, limit its use. Brown dithranol staining of treated skin (temporary) and fabrics or bathroom fittings (permanent), is common to all dithranol treatment techniques, and reduces patient acceptability. Skin irritancy is also a problem. Involved psoriatic skin is more resistant to irritancy than the clinically normal peri-lesional skin
Synergy with other treatments
The addition of UVB phototherapy prolongs remission. Comparison of the Ingram and short contact dithranol therapies shows a similar outcome. Dithranol must only be used under expert guidance on the face and flexures, because of the risk of skin or eye irritancy.
This information forms part of the current BAD guidance document for the general management of psoriasis. Other section in the document comprise: