Morphea-like lesion following topical endectocide application in a cat

Background – Scleroderma is a rare chronic disease of connective tissues that may affect the skin in humans. Although still unclear, its aetiology may be related to drug reactions. To date, scleroderma has been reported in only a few dogs and one cat. Case report – Localized (morphea‐like) scleroderma was diagnosed in a 3‐year‐old intact male Persian cat that developed a nonpruritic, well‐demarcated alopecic plaque a few days after topical application of a ‘spot‐on’ solution containing praziquantel and emodepside. The lesion occurred at the site of application at the dorsal cervical region, and was characterized histologically by fibrosing dermatitis. There was no response to systemic treatment with pentoxifylline. Following topical therapy with minoxidil 5% for 30 days, hair regrowth occurred, and the lesion had completely disappeared after 60 days. Conclusions and clinical importance – The relationship between the alopecic plaque and the topical application of the spot‐on solution cannot be proved; however, according to the Naranjo scale, which estimates the probability of adverse drug reactions, this case could be classified as a ‘possible’ reaction to one of the components of the product. Sclerodermoid reactions have not been described as a cutaneous drug eruption in veterinary medicine, so this case may possibly represent the first such idiosyncratic reaction to one of the applied substances. Furthermore, to the best of the authors’ knowledge, this is the second report of a morphea‐like lesion in a cat.