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Contact sensitization to N-(cyclohexylthio)phthalimide
Johannes Geier1, Holger Lessmann, Peter J Frosch
1Information Network of Departments of Dermatology (IVDK), Georg August University, Göttingen, Germany. jgeier@med.uni-goettingen.de
Contact Dermatitis
|March 19, 2003
Summary
Patch testing for N-(cyclohexylthio)phthalimide (CTP) in rubber allergies revealed that 0.5% concentration is optimal for identifying true allergies. Lower concentrations missed cases, while higher concentrations yielded false positives.
Area of Science:
- Dermatology
- Allergology
- Occupational Health
Background:
- Previous studies indicated high sensitization rates to N-(cyclohexylthio)phthalimide (CTP), a rubber chemical.
- The clinical relevance of positive patch test reactions to CTP and the appropriate test concentration were previously undetermined.
Purpose of the Study:
- To evaluate the diagnostic accuracy of different concentrations of CTP in patch testing for contact allergy.
- To determine the optimal concentration of CTP for reliable detection of CTP allergy in patients.
Main Methods:
- The German Contact Dermatitis Research Group (DKG) conducted patch testing with CTP at 0.25%, 0.5%, and 1% concentrations.
- 1936 patients were tested across 30 dermatology departments between June 1999 and December 2000.
- Analysis included reaction indices, patient characteristics, and concomitant sensitizations to other rubber chemicals.
Main Results:
- A total of 56 patients (2.9%) showed positive reactions to CTP.
- 52 patients reacted to 1% CTP, 21 to 0.5% CTP, and 9 to 0.25% CTP.
- 34 patients positive to 1% CTP did not react to lower concentrations, suggesting false positives. 0.25% CTP missed most true allergies.
Conclusions:
- A positive reaction to 0.5% CTP was identified as a reliable indicator of true contact allergy.
- The DKG will continue using 0.5% CTP in their standard rubber series for patch testing.
- Further research is needed to clarify the relevance of positive CTP reactions and identify causative exposures in allergic patients.