CURIO ITALIAN GREYHOUNDS
Quality without Compromise since 1987
have included information about this condition on our website so that it is in a
convenient location for those that might encounter it in one of their own dogs,
or if they experience symptoms that they don't know how to identify.
If you would like to read Ditto's Story, you can do so by following this link. If you have questions that I might be able to answer, please contact me.
Masticatory Muscle Mysositis (MMM) appears to be a breed problem in many large breed of dogs, including but not limited to:
German Shepherd Dogs
All Retrievers (Goldens and Labradors make up most reported cases in this group)
Old English Sheepdogs
This immune-mediated, focal inflammatory myopathy selectively affects the muscles of mastication and can occur in dogs less than 6 months of age, although the condition primarily affects young and middle-aged dogs and is unrelated to gender. While most cases occur in large breeds of dogs, it can affect any breed. (The incidence of this in Italian Greyhounds seems to be moderate, based on the information we have. We have found information on only six other affected dogs nationwide. I'm sure the numbers are higher, as many cases go unreported or undiagnosed) **(updated, October 2005...it has been brought to our attention that there are a number of other IGs diagnosed with this condition, including two in one litter. I have spoken with the breeders/owners of several of these dogs soon, so that we can compare information and pedigrees of these dogs to the ones we already know of.)
While most veterinarians are hesitant to say it's an inherited condition, it has been witnessed in lines and in litters of affected individuals.
This condition used to be described as two separate disorders: (1)eosinophilic myositis and (2) atrophic myositis. It is currently felt that these are manifestations of the same disease now called masticatory myositis. (MMM) is a canine inflammatory disorder, most likely immune-mediated,selectively involving the masseter, temporal, and pterygoid muscles of mastication. These muscles are used to grind and chew food prior to swallowing.(In layman's terms, these are the muscles in the top and sides of the face, including the cheek muscles, that assist in opening and closing the mouth)
Five muscle groups in the dog are involved in the process of mastication - four muscles are responsible for closing the mouth and one with opening the mouth. The tempoallis muscles and the masseter muscles are primarily the muscles used to powerfully close the jaws.
in mind that these muscles must also relax in order for the mouth to open. Since
these two muscles are the largest muscles which close the jaw, when they become
involved in masticatory myositis, the primary clinical sign is trouble in opening
chronic form usually is evident when the dog's head appears "sunken",
especially the top of the head. Sever and recurrent muscle damage leads to scar
tissue formation and atrophy or shrinking of the muscle. This scar tissue is
non-functional and these dogs often cannot open their mouths more than 1/2-1
inch. The dog's head often appears "skull-like" with a prominent
external sagittal crest (the bony ridge on top of the head) and the eyes are
sometimes enophthalmic or sunken due to loss of the muscle mass behind them
(fig.3). In the chronic form, laboratory findings are often normal. The CPK-MM
is usually normal due to the fact that there is little muscle left to produce
the enzyme. The dogs are normal otherwise and non-painful, although the mouth
cannot be opened.
Laboratory diagnosis is made by detection of circulating antibodies against type 2M fibers, a unique fiber type present only in the muscles of mastication(the temporalis and/or masseter muscles). These antibodies may play a role in the immune system attack on these muscle fibers. Evaluation of a muscle biopsy is necessary for confirmation of the diagnosis and in prognosis for return of jaw function and muscle mass as determined by the amount of myofiber destruction and fibrosis.
Immunosuppressive dosages of corticosteroids should be used until jaw function returns to normal and serum CK is within the reference range. The dosage should then be decreased until the lowest alternate day dosage is reached that keeps the dog free of clinical signs. In some dogs, prone to relapses, this must be maintained on continuous alternate day therapy over the dog's lifetime. This dosage should be continued for an additional 4-6 months since clinical signs will reoccur if treatment is stopped too soon or an inadequate dosage is used initially
Surgery is sometimes necessary to allow some return of jaw function. Often the insertion of the temporal muscle on the lower jaw is surgically incised and released. This may free up the jaw enough for the dog to be functional.
Fortunately, this is not a common disease, but one that veterinarians and owners need to be aware of.
This information was compiled from a number of veterinary sites, as well as newsletters and seminar transcripts.