Parthenium dermatitis presenting as photosensitive lichenoid eruption. A new clinical variant.

Parthenium hysterophorus is the commonest cause of airborne contact dermatitis (ABCD) in India. The disease usually manifests as itchy erythematous, papular, papulovesicular and plaque lesions on exposed areas of the body. Rarely, however, the disease may present as actinic reticuloid or photocontact dermatitis. We have observed a different clinical variant of this disease where certain patients with Parthenium dermatitis have presented with discrete, flat, violaceous papules and plaques on exposed areas of the body closely simulating photosensitive lichenoid eruption. We had 8 patients, 6 males and 2 females between 30 and 62 years of age, with itchy, violaceous, papules and plaques on the face, neck, ears, upper chest and dorsa of the hands for 6 months to 6.5 years. Four of these patients had a history of improvement of the lesions up to 30% in winter and aggravation of lesions on exposure to sunlight. There was no personal or family history of atopy. Cutaneous examination in all patients revealed multiple flat, violaceous, mildly erythematous papules and plaques on the forehead, sides and nape of neck, ears, 'V' area of the chest, and extensor aspects of the forearms and hands. Skin biopsies from these lesions showed features of chronic non-specific dermatitis. Patch testing with standardized plant antigens showed a positive patch test reaction to Parthenium hysterophorus in all patients, with a titre of contact hypersensitivity (TCH) varying from undiluted to 1 : 100. We conclude that Parthenium dermatitis may occasionally present with lesions very similar to the lesions of photosensitive lichenoid eruption in morphology and distribution. This clinical presentation of Parthenium dermatitis needs to be recognized to avoid misdiagnosis.