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CASE SUMMARY: A 4-year-old female spayed domestic shorthair cat was presented with facial swelling, ocular discharge and intermittent bilateral exophthalmos. Haematology revealed mild eosinophilia. Serum biochemistry showed a markedly elevated creatine kinase activity. MRI of the head revealed diffuse and severe changes of the masticatory muscles, including irregular areas compatible with fluid or necrosis within the abnormal muscle tissue. Cytological analysis of the left temporal muscle revealed eosinophilic and macrophagic inflammation. Bacterial and fungal cultures were negative. Serological titres against Toxoplasma gondii were compatible with previous exposure. A canine ELISA against masticatory muscle type IIM fibre proteins was positive at 1:4000 (reference interval <1:100). Histopathological examination of the left temporalis muscle revealed moderately severe and multifocal myositis. A diagnosis of immune-mediated masticatory myositis was made and immunosuppressive therapy was started. The cat initially responded to tapering doses of prednisolone, but subsequent relapses required therapy modulation. At the time of writing, 27 months after the initial diagnosis, the cat was in remission, but was diagnosed with diabetes mellitus, probably secondary to chronic glucocorticoid use. RELEVANCE AND NOVEL INFORMATION: To our knowledge, this is the first case report to describe the MRI appearance of masticatory myositis in a cat and the second to describe the clinical presentation, histopathology, response to treatment and outcome in a cat with this condition.
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BACKGROUND: Identification of perpetuating factors, such as otitis media (OM), is important for the successful management of canine chronic otitis externa (OE). HYPOTHESIS/OBJECTIVES: Occult OM can occur in cases of chronic OE; a focused magnetic resonance imaging (MRI) examination is a useful tool in their management. ANIMALS: One hundred twenty one client-owned dogs presented for investigation and treatment of chronic OE between 2009 and 2018. METHODS AND MATERIALS: Mixed retrospective (74 dogs) and prospective (47 dogs) study of chronic OE cases without neurological signs, describing the MRI, otoscopic and cytological findings; comparing cases with and without MRI evidence of OM. RESULTS: A total of 123 MRI studies were analysed (two dogs scanned twice). A short, focused MRI scan allowed detection of inflammation of the mucosal bulla lining as well as excellent discrimination between avascular material and vascularised soft tissue in the tympanic cavity. OM was found in 41 of 197 (21%) ears with chronic otitis externa. On otoscopy, the tympanic membrane was intact in six of 41 ears (15%), ruptured in 16 of 41 (39%) and not visible in 14 of 41 (34%) [no data in five of 41 (12%)]. Analysis of cytological findings showed that the presence of rods was only associated with an increased likelihood of OM when found together with inflammatory cells. CONCLUSIONS AND CLINICAL IMPORTANCE: Occult OM is a not uncommon finding on MRI of dogs with chronic OE. A targeted MRI study ("bulla mini-scan") may be useful as part of the clinical investigations.