The value of the patch test in poison ivy dermatitis, with consideration of group reactions between rhus extract and turpentine, pyrethrum, ragweed oil and 3-geranyl catechol

Abstract 1.1. The results of my studies support the following more or less generally accepted opinions on the uses and limitations of the patch test in relation to poison ivy dermatitis: 1.1.a. Diagnostic: A positive patch test with a potent rhus extract does not prove the presence of dermatitis due to poison ivy, but simply indicates sensitization to the plant, past or present. The diagnostic value of the test is depreciated by the high incidence of positive reactions in the normal adult population. Perhaps greater diagnostic significance can be attributed to a positive test in children below the school age, but this general rule has exceptions. In my view a negative patch test eliminates past and present hypersensitiveness to Rhus toxicodendron; upon this point rests the chief value of the test in differential diagnosis of dermatitis due to poison ivy. No substantial evidence has been published, thus far, to indicate that a negative patch test occurs in persons who have become spontaneously or otherwise desensitized months or years after the attack of poison ivy dermatitis. 1.2.b. Therapeutic: The quantitative patch test is an important method of checking the value of treatment in this disease. 1.3.c. Prognostic: A positive patch test does not necessarily mean that the patient has had clinical dermatitis from poison ivy or will acquire it under ordinary conditions of exposure. The relation between the results obtained with the patch test and the acquisition of clinical disease depends probably on quantitative factors involving the degree of hypersensitiveness and the severity of exposure. Those showing positive patch tests are more apt to acquire a dermatitis from contact with rhus under ordinary conditions than those with negative patch tests, but the rule is not invariable; a relatively small number of adults in the United States who show negative patch tests may also subsequently develop hypersensitiveness to poison ivy with a clinical attack. A distinction should be made between immunity as indicated by a negative patch test and immunity as revealed by contact with the plant under ordinary conditions of exposure. There are apparently rare instances in which the most drastic methods of sensitizing the skin have failed to produce hypersensitiveness to poison ivy. 1.4.d. Experimental: The value of the patch test in experimental studies cannot be overstressed. 2.2. Evidence is presented to show that there is no apparent biologic relation between hypersensitiveness to poison ivy and that to fresh turpentines of various types or to α- and β-pinene. Group reactions may be encountered with old specimens of turpentine, and it is assumed, although proof is lacking, that this may have been due to an increase in the phenolic fraction of turpentine. This problem needs further study. 3.3. Evidence of a group relation between the active ingredient in poison ivy and pyrethrum or ragweed oil was not found. 4.4. Evidence is presented to show, in substantiation of the work of Landsteiner and Jacobs in guinea pigs, that, in man, 3-geranyl catechol is biologically related to the active principle in poison ivy. Hypersensitiveness to 3-geranyl catechol seems to be dependent on the unsaturated geranyl group in combination with the catechol configuration.