Extraocular myositis is an uncommon inflammatory myopathy restricted to the extraocular muscles in dogs. The pathogenesis is unknown but could involve an autoimmune response to antigenically distinct muscle fibers, similar to what occurs in masticatory myositis (1).
Extraocular myositis affects a variety of dog breeds; however, Golden Retrievers may be overrepresented. Age of onset is between 6 months and 8 years.
The most common clinical sign of extraocular myositis is acute-onset bilateral exophthalmos; however, unilateral exophthalmos is possible. Visual deficits and increased intraocular pressures have been observed.
Diagnosis of extraocular myositis is based on history and clinical signs. Although muscle biopsy results may provide a definitive diagnosis, muscle biopsy is typically not necessary and carries risk of ocular injury.
Treatment typically involves immunosuppressive doses of steroids (eg, prednisone/prednisolone, 1–2 mg/kg, PO, every 24 hours [2]). Steroid therapy is often gradually decreased after several weeks. However, many patients need long-term treatment, and steroids may need to be restarted if clinical signs return after stopping therapy.
The prognosis for dogs with extraocular myositis appears to be favorable.
For other inflammatory myopathies in dogs, see the Overview for this chapter.
For More Information
Williams DL. Extraocular myositis in the dog. Vet Clin North Am Small Anim Pract. 2008;38(2):347-359, vii.
References
Allgoewer I, Blair M, Basher T, et al. Extraocular muscle myositis and restrictive strabismus in 10 dogs. Vet Ophthalmol. 2000;3(1):21-26. doi:10.1046/j.1463-5224.2000.00100.x
Adegboye O. Extraocular myositis in a female puppy. Open Vet J. 2015;5(1):42-44.
