Can patch testing with methylchloroisothiazolinone/methylisothiazolinone be optimized using a new diagnostic mix? – A multicenter study from the Swedish Contact Dermatitis Research Group

Abstract

Background: Methylchloroisothiazolinone/methylisothiazolinone (MCI/MI) and methylisothiazolinone (MI) are tested to detect contact allergy to these isothiazolinones.Objectives: To study if an aqueous patch test preparation with MCI and MI in a mix of 0.015% and 0.2%, respectively, detects more contact allergies than the commonly used preparations of MCI/MI in 0.02% aq. and MI in 0.2% aq.Methods: A total of 1555 patients with dermatitis in five Swedish dermatology departments were tested consecutively with MCI/MI 0.215% aq., MCI/MI 0.02% aq., and MI 0.2% aq.Results: The share of contact allergy to MCI/MI 0.215% aq., MCI/MI 0.02% aq., and MI 0.2% aq. varied in the test centers between 7.9% and 25.9%, 3.2% and 10.3%, and 5.8% and 12.3%, respectively. MCI/MI 0.215% aq. detected significantly more patch-test positive individuals than both MCI/MI 0.02% aq. (P < .001) and MI 0.2% aq. (P < .001), as well as either one of MCI/MI and MI (P < .001). In the patients only reacting to MCI/MI 0.215% aq., 57.7% were recorded as having a dermatitis that was explained or aggravated by exposure to either MCI/MI or MI. Conclusion:The results speak in favor of replacing the preparations MCI/MI 0.02% aq. and MI 0.2% aq. with MCI/MI 0.215% aq. as the screening substance in the Swedish baseline series, which has been implemented in 2020. K E Y W O R D Sallergic contact dermatitis, contact sensitization, delayed hypersensitivity, methylchloroisothiazolinone/methylisothiazolinone (MCI/MI), mix, patch testing

Patch Testing With Methylchloroisothiazolinone/Methylisothiazolinone Using a New Diagnostic Mix—A Multicenter Study From the International Contact Dermatitis Research Group

“…The results from this multicenter study are in line with the aforementioned study performed within the Swedish Contact Dermatitis Research Group, 13 and in the updated ICDRG baseline series from 2019, MCI/MI 0.02% aq and MI 0.2% aq were replaced by MCI/MI 0.215% aq 25 …”

“…Despite this, the total score was 22, which rendered this study to be classified as a multicenter patch test study with a high quality. 24 The results from this multicenter study are in line with the aforementioned study performed within the Swedish Contact Dermatitis Research Group, 13 and in the updated ICDRG baseline series from 2019, MCI/MI 0.02% aq and MI 0.2% aq were replaced by MCI/ MI 0.215% aq. 25…”

“…[21][22][23] However, the Swedish study showed that MCI/ MI and MI positive tests rarely appear late. 13 It was shown that 4.9% of the individuals with contact allergy to MCI/MI 0.215% aq, 5.4% of those with contact allergy to MI 0.2% aq, and 2.7% of those with contact allergy to MCI/MI 0.02% aq would have been missed if readings had only been performed on day 3 or 4. In the present study, a day 7 reading was not mandatory because each center followed its usual regimen.…”

“…For some allergens, this is particularly important, such as for corticosteroids, gold, and isocyanates 21–23 . However, the Swedish study showed that MCI/MI and MI positive tests rarely appear late 13 . It was shown that 4.9% of the individuals with contact allergy to MCI/MI 0.215% aq, 5.4% of those with contact allergy to MI 0.2% aq, and 2.7% of those with contact allergy to MCI/MI 0.02% aq would have been missed if readings had only been performed on day 3 or 4.…”

“…The prestudy in Malmö implied using a concentration of MI in the MCI/MI mix of 2000 ppm and patch testing consecutive patients with dermatitis in a stepwise manner, ensuring that no adverse effects were seen before proceeding with a higher concentration. A detailed scheme on how this was achieved is published, describing testing to this new mix 13 …”