By neuropetvet
Extraocular myositis is an uncommon inflammatory myopathy involving only the extraocular muscles. It is thought to be an immune-mediated condition, possibly the result of antibodies directed against an autoantigen of specific myofibers found only in the extraocular muscles.
Signalment
This condition occurs most commonly in young adult dogs (mean age 24 months in one case series of 37 dogs), but reported ages have been between 6 months and 11 years of age. Golden Retrievers are overrepresented. In two reports, Golden Retrievers accounted for 21 of 37 patients and 6 of 10 patients, respectively. Other reported breeds include: Bernese Mountain Dog, Dachshund, German Pointer, German Shepherd, Great Dane, Hovart, Japanese Spitz, Labradoodle, Labrador Retriever, mixed breed dogs, Rottweiler, and Welsh Corgi. There does not appear to be a gender bias.
Extraocular myositis is an uncommon inflammatory myopathy involving only the extraocular muscles. It is thought to be an immune-mediated condition, possibly the result of antibodies directed against an autoantigen of specific myofibers found only in the extraocular muscles.
Signalment
This condition occurs most commonly in young adult dogs (mean age 24 months in one case series of 37 dogs), but reported ages have been between 6 months and 11 years of age. Golden Retrievers are overrepresented. In two reports, Golden Retrievers accounted for 21 of 37 patients and 6 of 10 patients, respectively. Other reported breeds include: Bernese Mountain Dog, Dachshund, German Pointer, German Shepherd, Great Dane, Hovart, Japanese Spitz, Labradoodle, Labrador Retriever, mixed breed dogs, Rottweiler, and Welsh Corgi. There does not appear to be a gender bias.
Clinical signs
Almost all dogs are presented for evaluation of bilateral exophthalmos. Unilateral exophthalmos is uncommon, but has been reported. Blindness was reported in one dog.
Neurological & physical exam
The neurological exam is usually normal outside of ophthalmic changes. Most dogs have bilateral exophthalmos, giving them a characteristic "shocked" or "stunned" appearance. A small number of dogs showed other changes, such as strabismus, exotropia (divergent strabismus) and chemosis.
Diagnosis
A presumptive diagnosis is typically made based on the characteristic clinical signs described above in patients with no other signs of neurological dysfunction. Intraocular pressures are almost always normal; it was elevated in the one dog that was reported with blindness. Schirmer tear test results are sometimes elevated, but the significance of this finding is uncertain. Other diagnostic tests can be performed to further support the diagnosis, such as orbital ultrasonography, MRI, electromyography (EMG), fine-needle aspiration, or biopsy of extraocular muscles.
Almost all dogs are presented for evaluation of bilateral exophthalmos. Unilateral exophthalmos is uncommon, but has been reported. Blindness was reported in one dog.
Neurological & physical exam
The neurological exam is usually normal outside of ophthalmic changes. Most dogs have bilateral exophthalmos, giving them a characteristic "shocked" or "stunned" appearance. A small number of dogs showed other changes, such as strabismus, exotropia (divergent strabismus) and chemosis.
Diagnosis
A presumptive diagnosis is typically made based on the characteristic clinical signs described above in patients with no other signs of neurological dysfunction. Intraocular pressures are almost always normal; it was elevated in the one dog that was reported with blindness. Schirmer tear test results are sometimes elevated, but the significance of this finding is uncertain. Other diagnostic tests can be performed to further support the diagnosis, such as orbital ultrasonography, MRI, electromyography (EMG), fine-needle aspiration, or biopsy of extraocular muscles.
Treatment
Most dogs are treated with immunosuppressive doses of prednisone (1-2 mg/kg/day x 2 weeks followed by a gradual taper over several months). Some patients have also been treated with azathioprine.
Prognosis
The prognosis for recovery appears to be good if treated early.
Further reading
Allgoewer I, Blair M, Basher T, et al. Extraocular muscle myositis and restrictive strabismus in 10 dogs. Vet Ophthalmol 2000;3:21-26.
Azoulay T, Jongh O. Extraocular myositis and comparative pathology: two case reports in the dog. J Fr Ophtalmol 2011;34:737.e1-5.
Carpenter JL, Schmidt GM, Moore FM, et al. Canine bilateral extraocular polymyositis. Vet Pathol 1989;26:510-512.
Mitra S. Eosinophilic myositis of the extraocular muscles. A case report. Tierarztl Prax Ausg K Klientiere Heimtiere 1998;26:336-340.
Williams DL. Extraocular myositis in the dog. Vet Clin North Am Small Anim Pract 2008;38:347-359.
Most dogs are treated with immunosuppressive doses of prednisone (1-2 mg/kg/day x 2 weeks followed by a gradual taper over several months). Some patients have also been treated with azathioprine.
Prognosis
The prognosis for recovery appears to be good if treated early.
Further reading
Allgoewer I, Blair M, Basher T, et al. Extraocular muscle myositis and restrictive strabismus in 10 dogs. Vet Ophthalmol 2000;3:21-26.
Azoulay T, Jongh O. Extraocular myositis and comparative pathology: two case reports in the dog. J Fr Ophtalmol 2011;34:737.e1-5.
Carpenter JL, Schmidt GM, Moore FM, et al. Canine bilateral extraocular polymyositis. Vet Pathol 1989;26:510-512.
Mitra S. Eosinophilic myositis of the extraocular muscles. A case report. Tierarztl Prax Ausg K Klientiere Heimtiere 1998;26:336-340.
Williams DL. Extraocular myositis in the dog. Vet Clin North Am Small Anim Pract 2008;38:347-359.
Other article notes:
Notes by vetinfo
Extraocular myositis (EOM) is extremely rare and generally only affects Golden Retrievers. The disease, first diagnosed in 1991, occurs when the extraocular muscles become inflamed. Unlike MMM that occurs when the antibodies attack 2M fibers, it's unknown why the eye muscles are attacked.
Dogs with this form of myositis have a startled expression with wide open eyes that may appear to pop out. Pet owners might notice their dogs third eyelid is protruding. The dogs do not appear to be in pain and are usually one to three years old when EOM becomes noticeable.
Because this is a relatively new disease, research is still ongoing. In studies performed on animals showing the signs of EOM, almost all dogs were female and of breeding age. There are a handful of male dogs who've developed EOM, but research finds it is most common in females by a ratio of about four to one.
Treatment for this inflammatory disease involves corticosteroids. Prednisolone is the prescription medication used and many dogs are back to normal within a month. Dogs given the corticosteroids for only a few days usually had a relapse of the disease after approximately two to three months. For this reason, it is important to follow your veterinarian's treatment plan.
Extraocular myositis (EOM) is extremely rare and generally only affects Golden Retrievers. The disease, first diagnosed in 1991, occurs when the extraocular muscles become inflamed. Unlike MMM that occurs when the antibodies attack 2M fibers, it's unknown why the eye muscles are attacked.
Dogs with this form of myositis have a startled expression with wide open eyes that may appear to pop out. Pet owners might notice their dogs third eyelid is protruding. The dogs do not appear to be in pain and are usually one to three years old when EOM becomes noticeable.
Because this is a relatively new disease, research is still ongoing. In studies performed on animals showing the signs of EOM, almost all dogs were female and of breeding age. There are a handful of male dogs who've developed EOM, but research finds it is most common in females by a ratio of about four to one.
Treatment for this inflammatory disease involves corticosteroids. Prednisolone is the prescription medication used and many dogs are back to normal within a month. Dogs given the corticosteroids for only a few days usually had a relapse of the disease after approximately two to three months. For this reason, it is important to follow your veterinarian's treatment plan.