Dynamic exophthalmos and lateral strabismus in a dog caused by masticatory muscle myositis.
METHODS
A 5.5-year-old neutered male mixed-breed dog was presented for evaluation of a 5-month history of deviation of the right globe upon opening the mouth and a 1-month history of conjunctivitis in the same eye. Clinical findings, diagnostic imaging results, treatment and follow-up are described.


RESULTS
When the mouth was opened, the right globe deviated rostrally and laterally. There was no pain or resistance to opening the mouth, or resistance to retropulsion of the globe. No other abnormalities were observed. Computed tomography was performed, revealing a contrast-enhancing region associated with the right masseter muscle impinging into the right orbit; this was more pronounced with the mouth open. Cytology revealed a small number of mildly to moderately atypical mesenchymal cells. Histopathology was consistent with polyphasic myositis, with a predominance of lymphocytes and plasma cells. No infectious agents were identified. Serum antibody titers for Toxoplasma gondii and Neospora caninum were negative. Serum titers for 2 M antibody were positive at 1:500, consistent with a diagnosis of masticatory muscle myositis.


RESULTS
Therapy with prednisone was initiated. During a follow-up period of 5 months, there was no recurrence of clinical signs, and the dose of prednisone was reduced by 25%.


CONCLUSIONS
To the authors' knowledge, this is the first reported case of masticatory muscle myositis causing dynamic exophthalmos and strabismus in a dog.
Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, 2015 SW 16th Avenue, Gainesville, FL, 32610, USA.
Sarah L
SL
Czerwinski
Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, 2015 SW 16th Avenue, Gainesville, FL, 32610, USA.|Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, 2015 SW 16th Avenue, Gainesville, FL, 32610, USA.
Caryn E
CE
Plummer
New England Veterinary Center and Cancer Care, 955 Kennedy Road, Windsor, CT, 06095, USA.
Shari M
SM
Greenberg
Department of Infectious Diseases and Pathology, College of Veterinary Medicine, University of Florida, 2015 SW 16th Avenue, Gainesville, FL, 32610, USA.
William F
WF
Craft
Department of Infectious Diseases and Pathology, College of Veterinary Medicine, University of Florida, 2015 SW 16th Avenue, Gainesville, FL, 32610, USA.
Julia A
JA
Conway
Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, 2015 SW 16th Avenue, Gainesville, FL, 32610, USA.
Mayrim L
ML
Perez
Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, 2015 SW 16th Avenue, Gainesville, FL, 32610, USA.
Kirsten L
KL
Cooke
Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, 2015 SW 16th Avenue, Gainesville, FL, 32610, USA.
Matthew D
MD
Winter
D000818:Animals; D000893:Anti-Inflammatory Agents / Q000627:therapeutic use; D004283:Dog Diseases / Q000175:diagnosis* / Q000209:etiology / Q000473:pathology; D004285:Dogs; D005094:Exophthalmos / Q000175:diagnosis / Q000209:etiology / Q000473:pathology / Q000662:veterinary*; D008297:Male; D008410:Masticatory Muscles; D009220:Myositis / Q000150:complications / Q000175:diagnosis / Q000188:drug therapy / Q000662:veterinary*; D011241:Prednisone / Q000627:therapeutic use; D013285:Strabismus / Q000175:diagnosis / Q000209:etiology / Q000473:pathology / Q000662:veterinary*
D000893:Anti-Inflammatory Agents; D011241:Prednisone
dog; exophthalmos; masticatory; muscle; myositis; strabismus