Key words: agricultural workers' diseases; occupational contact dermatitis; psoriasis; Köbner phenomenon; isomorphic phenomenon; contact allergy; thiuram; rubber; agricultural chemicals; seed protectants.
Hybrids of psoriasis and occupational contact allergy are rarely reported.
A woman had been a farmer since the age of 16. Besides field crops, there was also greenhouse vegetable production on the farm. When she was 23, psoriasis appeared on her trunk and limbs, though not on the hands. 8 years later, hand dermatitis developed in relation to contact with pesticides and working in the greenhouses. A few years later, she had had to discontinue wearing rubber gloves and boots, because of a burning sensation and eczema at contact sites.
Examination showed psoriatic plaques over the patient's trunk and limbs. There was confluent erythema, hyperkeratosis with scaling and fissuring on the palms of the hands and lichenification on the dorsa. The distal forearms were also involved, with parakeratotic papules scattered along the borders of the dermatitis. The patient underwent a standardized diagnostic procedure for farmers' occupational diseases (1).
Biopsy from the involved forearm skin showed granulocytic infiltration of dermal papillae; there were foci of parakeratosis and spongiosis in the epidermis, the granular layer being preserved. This picture thus comprised features of both psoriasis and dermatitis. Prick and intracutaneous tests with environmental and occupational allergens were all negative. Patch tests included European standard series (Chemotechnique, Malmö, Sweden), rubber series (Jaworski, Katowice, Poland) and pesticide series (Institute of Agricultural Medicine, Lublin, Poland). A positive reaction was recorded to thiuram mix 1% pet. on D3, D4 and D7. The test reaction corresponded with a ++ score - there was pronounced erythema and infiltration, though pustules were present instead of typical vesicles.
Within 2 weeks, a parakeratotic plaque of psoriasis had developed on the positive patch test site. This Köbner (isomorphic) phenomenon was consistent with the above-mentioned parakeratotic patches at the borders of the eczema. Besides rubber gloves and boots, seed protectants were identified as a major source of thiuram in the patient's work environment. She was regularly treating vegetable seeds with such protectants, which according to the products' labels consisted of up to 32% thiuram.
Köbnerizing occupational contact dermatitis from thiuram has previously been described only once - in a nurse allergic to rubber gloves (2). Nurses' gloves were also the cause of recurrent erythroderma in a thiuram-allergic patient with psoriasis (3).
A pustular patch test reaction to thiuram has previously been seen in a rubber factory worker with occupational pustulosis palmaris; in that case, however, there was no pre-existing psoriasis and no köbnerization (4). Allergy to thiuram is relatively frequent among farmers - it was found in 7% cases of disabling occupational dermatitis (5).
The present case, besides the rarity of the clinical picture, clearly shows that seed protectants and seeds treated with those chemicals are relevant sources of thiuram in agriculture and horticulture.
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