Acquired perforating calcific collagenosis after topical calcium chloride exposure

A 24-year-old healthy man presented with a 6-week history of numerous umbilicated coalescing erythematous papules with some scale and crust on his anterior medial thighs. The eruption began 1 to 2 weeks after he spilled calcium chloride rock salts on his pants while salting the sidewalk during a snow storm. The salts dissolved and remained in contact with his skin for at least 4 hours until he was able to change clothes. A skin biopsy shows thick and thin collagen fibers with partial calcification in the papillary and upper reticular dermis associated with a sparse infiltrate of neutrophils, lymphocytes and mononuclear histiocytes. There are foci of transepidermal elimination of calcified fibers with adjacent epidermal hyperplasia and ortho- and parakeratosis. Von Kossa stain highlights calcification of the fibers, and trichrome stain confirms the fibers are collagen. A Verhoeff-van Gieson stain shows no abnormality of elastic fibers. The patient was treated with topical betametasone diproprionate cream twice daily for 3 weeks, as well as a short course of oral levofloxacin and topical gentamicin cream. The lesions resolved over 3 weeks with residual scarring. We report a unique case of acquired perforating calcific collagenosis secondary to topical calcium chloride exposure.