"Eosinophilic" means the presence of eosinophils, a type of white blood
cell within the affected area. "Myositis" means inflammation of
muscle fibres. In its acute form, it is characterised by the
rapid accumulation of large numbers of these cells within the muscles,
causing them to be swollen and painful. If the muscles associated
with chewing are affected it makes it very painful for the dog to
eat. Sometimes the swelling can be so severe that the eyes bulge
or the mouth is prevented from opening more than several
centimetres. Once the muscle fibres have been damaged, there is
little oportunity for them to repair themselves so they are replaced by
scar tissue which is inelastic and makes it even more difficult for the
dog to open its mouth.
It is unknown
what starts this process, but it is generally accepted that the immune
system is dysfuntional and starts to attack the muscles with
antibodies. The limb muscles are generally not affected at the
same time as the facial muscles because they have a different
structure. Sufferers of this condition can be generally quite
weak as they are undernourished due to the inabilty to open the mouth
As soon as
possible it is important to limit the damage to the muscle
fibres. This is achieved by using steroids which are given for
short periods of time, during attacks only, or on a lowest dose, semi
continuous basis to control symptoms.
McNally BVSC MRCVS
affects the masticatory muscles - the large muscles on the top and
of the head which act to close the jaw. These muscles have a unique
protein composition. Masticatory muscle myositis is an immune-mediated
in which the body’s immune system attacks the unique muscle protein
in the masticatory muscles. This causes the muscles to become painful
swollen initially, and the muscles will atrophy as the disease
Opening the mouth is particularly painful.
How is masticatory muscle myositis inherited?
What breeds are affected by masticatory muscle myositis?
The German shepherd dog is most frequently affected, but this disease
is also reported in other large breed dogs, including the English
pointer and springer spaniel.
For many breeds and many disorders, the studies to determine the mode
of inheritance or the frequency in the breed have not been carried out,
or are inconclusive. We have listed breeds for which there is a
consensus among those investigating in this field and among veterinary
practitioners, that the condition is significant in this breed.
What does masticatory muscle myositis mean to your dog & you?
Many dogs affected with masticatory muscle myositis will improve with
How is masticatory muscle myositis diagnosed?
Your veterinarian will suspect this disease if your dog has painful,
swollen masticatory muscles, with pain on opening the jaw. The
diagnosis can be confirmed with a muscle biopsy to examine the cells
with a microscope. Special techniques may be used to test for specific
How is masticatory muscle myositis treated?
Affected dogs are usually treated medically, with glucocorticoids such
as prednisone. Most dogs improve with drug therapy, although the
treatment may be long-term.
Affected animals should not be bred.
INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Kornegay JN. 1995. Disorders of the skeletal muscles. In EJ Ettinger
and EC Feldman (eds) Textbook of Veterinary Internal Medicine,
p.727-736. WB Saunders Co., Toronto.
Ackerman L. 1999. The Genetic Connection: A Guide to Health Problems in
Purebred Dogs, p. 121. AAHA Press,Lakewood, Colorado.
Copyright © 1998 Canine Inherited
Disorders Database. All rights reserved.Revised: May 16, 2002.
This database is a joint initiative of the Sir James Dunn Animal
Welfare Centre at the Atlantic Veterinary College, University of Prince
Edward Island, and the Canadian Veterinary Medical Association.
with kind permission from:-
Crook, DVM,Coordinator, Sir James Dunn Animal Welfare Centre, Atlantic
Veterinary College,University of Prince Edward Island, 550 University
Ave.Charlottetown, PEI C1A 4P3
The above information is simply
informational. It's intent is not to replace the advice of a
veterinarian nor to assist
you in making a diagnosis of your pet. Please consult with your own
veterinarian for confirmation of any diagnosis. Your pets life may
depend on it.