Acute Contact Dermatitis by Dithranol

Abstract

We report the case of a bricklayer who presented an outbreak of generalized psoriasis. After treatment with several topic preparations, the patient's lesions improved, but at the same time he developed an intensely pruritous eczema with pigmented lesions on the treated areas. Standard patch tests showed positivity to potassium dichromate, cobalt sulphate, and cobalt chloride, professionally related. Special patch tests performed with a series of the substances used in the treatment of the outbreak of psoriasis showed negative results with the exception of dithranol, which gave positivity to concentrations of 0.05%, 0.02%, 0.01%, and 0.005%, all in petrolatum. Fifty healthy controls patch-tested with dithranol at the same concentrations were negative to the latter three, but showed positivity to a concentration of 0.05%. The conclusions from this are as follows: (1) Dithranol and the identified oxydization products of this substance, danthron and dithranol dimer, are not responsible for either the irritation or pigmentation of the skin, and it is probable that compounds still not recognized added to that of dithranol could be responsible for adverse skin reactions. It has been suggested that dithranol dimer is oxidized before colorant is added, which may contribute to the formation of pigmentation. A recent published work did not support the hypothesis that the pigmentary system might be involved in dithranolinduced irritancy. (2) The ideal concentration for patch-testing patients suspected of sensitization to dithranol is 0.02% in petrolatum or acetone.