Clinical
History
A 7 year old M German Shepherd dog presented for an approximately
1 week history of bilateral exophthalmos
that was worse on the right side, swollen hemorrhaghic
third eyelids, firm and swollen facial muscles, and mild submandibular
lymphadenopathy (A,B,C). Although pain was reported on opening the jaw,
the dog did not have any difficulty eating.
Physical Examination
Abnormal findings on physical examination were localized
to the muscles of mastication and the eyes. The masticatory
muscles were firm and swollen, and there was marked enlargement
of submandibular lymph nodes. Ophthalmologic examination revealed
bilateral exophthalmos that was
worse on the right, protrusion and vascular engorgement of
the nictitating membrane bilaterally, focal corneal ulceration
in the right eye, anisocoria, and
negative direct pupillary light response and absent menace
reflex in the right eye. The dog was blind in the right eye.
Diagnostic Testing
CBC Unremarkable with the exception of decreased
platelets (30,000/ml; reference range 175-500,000)
Creatine kinase Mildly elevated (298 IU/L; reference range
10-200)
Total protein Elevated (95 g/L; reference range 52-82)
Globulin Elevated (62 g/L; reference range
25-45)
Antinuclear antibody titer Negative
2M antibody titer Positive at 1:1000 (reference range <
1:100)
Chest radiographs Normal
Diagnosis
Based on the clinical signs and the positive serum antibody
titer against masticatory muscle
type 2M fibers, a diagnosis of masticatory
muscle myositis (MMM) was made.
Since platelets were decreased on the initial CBC, a decision
was made not to perform a biopsy of the temporalis
muscle. A repeat CBC later showed the platelet count within
the reference range and it was concluded that initial count
was laboratory error.
Treatment
Prednisone therapy was initiated at immunosuppressive dosages and ophthalmic
ointments were used for treatment of the corneal ulceration.
Outcome
On reevaluation 7 days later, all clinical signs with the
exception of the blindness in the right eye had resolved (D,E,F).
A gradual tapering
dose of prednisone was planned for over the next 3 to 6 months.
Clinical signs were most likely a result of MMM due to swelling
of the temporalis and pterygoid
muscles. In one study (Gilmour et al 1992), ocular signs
including conjunctivitis, exophthalmos
and permanent blindness with optic nerve atrophy occurred
in 44% of the cases. Temporary blindness was also described
in a case report (Glauberg and Beaumont
1979). On reexamination 3 weeks following the initial presentation,
the dog was still blind in the right eye with no other clinical
signs of MMM.
References
Gilmour MA, Morgan RV, Moore
FM. Masticatory myopathy
in the dog: A retrospective study of 18 cases. J Am Anim
Hosp Assoc 28:300-306, 1992.
Glauberg A, Beaumont PR. Sudden
blindness as the presenting sign of eosinophilic
myositis: A case report. J Am Anim
Hosp Assoc 15:609-611, 1979.
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