Diagnosis and Further Treatment
Supportive care with intravenous fluids and syringe
feeding was initiated and potentiated sulphonamides were also added (15mg/kg/BID). Ocular lubricants
were used to prevent exposure keratitis in the left eye (Lacrilube overnight and Viscotears q4 hours in the day). Over the next 4 days the dog’s demeanor improved, the nystamus resolved
and the head tilt reduced in severity. The dog was discharged
to her owner at this point.
Although the positive 2M antibody titre confirms
a diagnosis of masticatory muscle myositis (MMM), the positive
Neospora IFAT also indicates an active Neospora infection.
The development of acute onset of neurological signs, lead
us to believe there was active Neospora infection within the
central nervous system. It was felt that there may also be
Neospora infection within the muscles, however review of the
muscle biopsies in light of this did not reveal any Neospora
cysts or tachyzoites; antibody staining
for Neospora was also negative. As masticatory muscle myositis
is an immune mediated condition it is possible that the Neospora
infection acted as a trigger for the development of 2M auto-antibodies.
Masticatory muscle myositis can lead to the rapid destruction of myofibers and fibrosis, and immunosuppressive therapy with corticosteroids
is indicated. In this case steroids were not added initially
due to the concern of worsening Neospora infection. Six weeks
of clindamycin and potentiated sulphonamides were prescribed, and after 3 weeks,
anti-inflammatory doses of corticosteroids were added. The
dosage was incrementally increased to an immunosuppressive
dose (1mg/kg/BID) whilst watching for worsening of the neurological
signs. The dog remained stable and the jaw movement increased
rapidly over the next 2 weeks. The prednisolone dose was then gradually reduced over the next 6 months.
The dog has now completed the 6 month tapering prednisolone course, and although a slight head tilt and the
absence menace response are still present, the dog has a very
good quality of life. The dog’s jaw opens close to a normal
range with normal prehension and chewing.
A severe and early onset form of masticatory myositis is seen in
Cavalier King Charles Spaniels, although this is yet to be
fully characterized (see our July 2005 case of the month).
With respect to the Neospora infection, this dog had never
been outside the owners’ garden, thus vertical transmission
was suspected. The dog had been bred by the owner and the
bitch was frequently walked on dairy farm land, a known risk
factor for Neospora infection (Kramer et al, 2004); Neospora
titres in the bitch did not indicate exposure to Neospora
(IFAT <1:100 ), and there were no clinical signs of infection.
Kramer L, De Riso L, Tranquillo V M, Magnino S & Genchi
C. Analysis of risk factors associated with seropositivity
to Neospora caninum in dogs. Veterinary
Record (2004) 154,692,693
Ruehlmann D, Podell M, Oglesbee M, Dubey J P. Canine Neosporosis:
A case report and literature review. Journal of the American
Hospital Association (1995) 31,174-183
C, Barton CL, Bergman R, Shelton
D. Masticatory muscle myositis: Pathogenesis, Diagnosis, and
Treatment. Comp Continuing Ed Small Animal. August 2004