Investigation of Anti-Myeloperoxidase Antibodies in a Dog with Bilateral Necrotizing Scleritis

Necrotizing scleritis is uncommon in dogs and presumed to be immune-mediated. Its clinical pattern and histopathology are similar to ocular lesions observed in humans suffering from granulomatosis with polyangiitis (GPA), formerly named Wegener's granulomatosis, where the pathogenesis revolves around anti-neutrophil antibodies (e.g., anti-myeloperoxidase). These antibodies are used to diagnose and follow-up the disease in humans, but variants that only affect the eyes often test negative. Here, we present the first case of canine necrotizing scleritis where measurement of anti-myeloperoxidase antibodies was attempted. A 1.5 year-old female Scottish Terrier was presented with bilateral deep multifocal scleromalacia, severe inflammation of corneal/uveal/retrobulbar tissues, perilimbal corneal oedema and neovascularization, hypotony, and mild exophthalmos. Corticosteroids and antibiotics had been administrated (topically and orally) without success. Due to painful multifocal scleral perforation with vitreal haemorrhage, the left eye underwent enucleation, so did the right eye one week later. The histopathology of the left eye revealed a neutrophilic and histiocytic scleral infiltration with extension of pyogranulomatous inflammation to the cornea, choroid, ciliary body, and orbital fat. Levels of plasma anti-myeloperoxidase antibodies were not statistically significant to those of 13 healthy dogs. Further research is warranted to investigate the presence and role of anti-neutrophil antibodies in canine necrotizing scleritis.