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A 44-year-old man presented with a two-and-a-half-year history of an itchy recurrent facial rash, occurring during the summer. He was employed at a company which made pyrethrins for insecticide manufacturers. His work included unloading and processing pyrethrum daisies (Tanacetum cinerariifolium) into pallets. He developed the rash after occupational exposure to the daisies, lasting 2–4 weeks each summer. Symptoms improved, though incompletely, after about 2 months post-exposure. He found hydrocortisone 1% cream unhelpful when symptomatic, instead noting increased plant dust adhesion to his face when using the cream. He had never noticed any reaction to insect spray containing pyrethroids. He had capeweed (Arctotheca calendula) growing around his home. There was no past history of skin disease such as atopic dermatitis. Examination showed facial erythema and mild glabellar scaling. A photograph taken during the season revealed facial scaling with eyelid involvement and mild serous discharge on the left cheek. A diagnosis of airborne contact dermatitis was made. He was prescribed pimecrolimus 1% cream twice daily for his face. His employer provided protective equipment (half-face respirator and goggles) to wear during exposure to the plant dust. Patch testing showed positive reactions (erythematous and papular) to a sample of the crop (T. cinerariifolium), carbamate mix, iodopropynyl butylcarbamate, lanolin, ammonium persulphate and betamethasone 17-valerate. He had equivocal reactions to mercapto mix and methylprednisolone aceponate, but did not react to Compositae mix, sesquiterpene lactone mix or a pyrethrum-based insect spray. Photopatch testing yielded positive reactions to the crop and lichen acid but not Compositae mix. Because the exposure is occupational, it is hoped that the use of protective equipment while working will provide adequate relief, given that the patient is not sensitive to other Compositae which he may encounter as an airborne allergen outside the workplace. Occupational pyrethrum dermatitis has been identified in the literature as being induced by sesquiterpene lactones, principally pyrethrosin.1 However, the components of the pyrethrum plant which actually have insecticidal properties are the pyrethrins, which are not sesquiterpene lactones. While pyrethrosin and pyrethrins are both contained in the plant, it is pyrethrins that are used in manufactured insecticides, which therefore are unlikely to provoke a reaction in workers occupationally sensitised to pyrethrosin.1 However, pyrethrin II has also been reported as an allergen.1 Sesquiterpene lactone mix contains alantolactone, costunolide and dehydrocostus lactone.2 However, the commercially available mix is not always adequate for diagnosing individuals sensitised to specific Compositae species.3 Compositae mix is a more sensitive reagent in detecting Compositae allergy.4 Compositae mix II is in the Australian baseline series for patch testing, containing extracts of Anthemis nobilis, Chamomilla recutita, Achillea millefolium, Tanacetum vulgare and Arnica montana, as well as parthenolide.5 We wish to highlight the utility of patch testing for specific potential allergens to which a patient may be exposed (in this case, the crop sample) rather than solely the commonly tested allergens such as sesquiterpene lactone or Compositae mix. None. The authors have no conflicts of interest to disclose. Patient consent was obtained for publication.
Rajagopalan et al. (Fri,) studied this question.