NEUROMUSCULAR CASE OF THE MONTH - JULY 2005
Masticatory muscle myositis in a young male Cavalier King Charles Spaniel
Contributed by Dr. Dana Graham
The pup was born
An initial DHPP vaccination was given by the breeder, and booster
DHPP and intranasal Bordatella vaccines were
given at 9 weeks of age. At that time, physical examination was
with normal limits with the exception of a small, reducible umbilical
hernia. The dog was also dewormed and
placed on preventative treatment for fleas. Ten days following the
second vaccination, the dog presented for lethargy and anorexia.
Physical and Neurological Examination
A change in facial features was noted with swelling
of the temporomandibular muscles and jaw pain. The dog was unable
to open the jaws more than 1-1.5 cm. Mild serous exudate was present from both nostrils, and there was mild ocular discharge
and conjunctivitis. The submandibular lymph nodes were also enlarged. The differential diagnosis included
acute masticatory muscle myositis or craniomandibular osteopathy. Treatment
was initiated with a non-steroidal anti-inflammatory (4 mg/kg SID)
and clavamox (22 mg/kg BID). Since there
was no improvement 24 hours later, prednisolone (1.5 mg/kg BID) was added.
On re-evaluation two days later, the
dog was brighter with decreased swelling of the masticatory muscles. The owner described that he was starting to play with chew
toys and eating gruel. The jaw was easier to open and lymph nodes
were decreased in size. At one week following initiation of prednisolone,
the dog developed diarrhea. Coccidia sp was identified and the dog treated. Ten days later masticatory muscle atrophy was noted and the owner, in spite
of recommendations to continue long term prednisone therapy, decreased
the prednisolone dosage to 2 mg/kg SID,
and weaned the dog off the prednisolone following only a three week course of treatment. Three weeks later,
there was reoccurrence of masticatory muscle swelling, decreased jaw mobility, and enlargement
of the submandibular lymph nodes.
Serum creatine kinase concentration 668 IU/L (reference 59-895)
Serum 2M antibody titer positive 1:4000 by ELISA
The positive 2M antibody titer confirmed the diagnosis of masticatory muscle myositis and prednisolone therapy was again prescribed. The dog again responded
to treatment and is now on an extended course with slow taper over
a 4 to 6 month period of time. Relapse of clinical signs is a common
occurrence in this myopathy if treatment
is not continued for an adequate period of time. A female, full
litter-mate was also noted to have had a “vaccine reaction”.
Conclusion by Dr. Diane Shelton
In a search of the database of the Comparative Neuromuscular
Laboratory over the years 2001-2005, masticatory muscle myositis was confirmed in 11 young
Cavalier King Charles Spaniels with onset at less than 6 months
of age. In several cases, onset followed within 10 days of vaccinations.
Although long-term information is not yet complete, there was resolution
of clinical signs of masticatory muscle myositis in most
cases. Of interest, other complications such as early onset hypothyroidism
and allergies were reported. Additional information will be provided
as more is learned about this early-onset masticatory muscle myositis in this breed.
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