Morphea-Like Lesion Following Topical Application of an Endectocide in a Cat
G. Seixas1; P. Taboada2
Morphea (scleroderma) is a rare chronic disease of connective tissues that may involve skin and internal organs in humans. It is rare in the dog, and very rare in cats. The cause is unknown. Vascular injuries with collagen production, autoimmune phenomena, and association with Borrelia burgdorferi have been speculated. In human medicine, it is known that sclerodermoid reactions can occur secondary to environmental chemicals (such as polyvinyl chloride), following local injections (such as vitamin K), or as side effect to systemically administered medication (such as bleomycin, taxanes, ergot alkaloids, and others). A three-year-old male Persian cat was presented with a history of a chronic focal alopecia for two months, which started a few days after the use of a "spot on" topical solution containing praziquantel and emodepside. According to the owner, the initial hair losing progressed rapidly into a non-pruritic alopecic plaque, and the cat was treated with dexamethasone at an unknown dosage that seemed to have stopped the progression of the lesion. At the time of clinical examination, it was noted a mildly-raised well-demarcated alopecic plaque, with 10 centimeters in diameter, tended toward the right shoulder at the interscapular region. Mild comedones and follicular casts were noted surrounding it. Fungal culture and skin scrapings were negative. Systemic itraconazole and topical chlorhexidine for 30 days showed no response. The biopsy findings revealed fibrosing dermatitis. The dermis was replaced by collagen bundles, and there was no evidence of inflammatory process; the epidermis was unremarkable. Hypotrichosis and follicular atrophy were noted. Suspected diagnosis included cicatricial alopecia or morphea. The cat was treated with systemic pentoxifylline for 70 days without any benefit. Therapy was then alternated to topical minoxidil at 5% solution. After 30 days of topical therapy, a marked regrowth of hairs was noted. The lesion could no longer be identified after 60 days of topical therapy. Distinction between cicatricial alopecia and morphea is difficult. The diagnosis of morphea was supported by clinical resolution (usually spontaneous) and fairly normal arrangement of collagen fibers. The presence of viable hair follicles lead to the use of minoxidil as a hair growth stimulator, but since morphea may be self limiting; the effect of this therapy cannot be evaluated. Morphea has not been described as a cutaneous drug eruption in veterinary medicine, and this case may represent an idiosyncratic reaction to one of the components of the product.