Scleromyxoedema in a dog

Background In humans, scleromyxoedema is a chronic progressive skin condition traditionally characterized by deposits of mucin, increased number of fibroblasts and fibrosis in the skin, and by systemic disease. Thyroid disease is typically absent. A monoclonal gammopathy is usually present, as are other comorbidities. Descriptions of scleromyxoedema in the veterinary literature are limited to a single feline case. One dog, previously reported as having papular mucinosis, exhibited features that matched the more current diagnostic criteria of scleromyxoedema. Objectives To describe generalized papular mucinosis in a dog with systemic illness and to compare the signs with those of human lichen myxoedematosus conditions, specifically scleromyxoedema. Results A nine‐year‐old female, spayed English springer spaniel dog presented with generalized papules and nodules (0.5–5 cm) on the body and proximal fore and hind limbs, sparing the face and distal limbs distal to carpi/tarsi. Larger nodules were erythematous. Nodules occurred in proximal limb muscles. The dog had concurrent osteoarthritis of the elbows and coxofemoral joints, developed generalized weakness, declined in health and was euthanized. Thyroid disease was lacking and a monoclonal gammopathy was not present. Histopathological evaluation revealed the classic triad of mucin, fibroblast proliferation and fibrosis with very mild inflammation, as described for humans. Conclusion and clinical importance We document scleromyxoedema in a dog with significant morbidity and features of the human disease. Recognizing the typical histopathology is important for identifying cases and to establish a diagnosis. Systemic evaluation is important to identify evidence of internal disease and associated comorbidities, which are common, variable, and impact classification and prognosis in humans.