An 8-year-old, 4.8-kg, spayed female dachshund presented with a 4-day history of progressive, bilateral exophthalmos.
Physical Examination. No pain or restriction was detected when opening the mouth. No pain, atrophy, or swelling of the temporalis or masseter muscles was noted. Complete ophthalmic examination revealed bilateral restrictive exophthalmos and nictitans elevation with slight exotropia (OD > OS), superficial corneal erosion OS, mild anterior uveitis OS, and distichiasis OU (Figure 1, above).
Figure 1. Bilateral extraocular photograph of the patient showing bilateral exophthalmos, slight exotropia (OD > OS), and bilater al elevation of the thir d eyelid. A focal, axial, superficial corneal erosion was also present in the left eye
Initial Diagnostics. Results of a CBC, chemistry profile, serum creatine phosphokinase (CK), and urinalysis were normal. Total thyroxine (T4) and triiodothyronine (T3), free T3 and T4, T3 and T4 autoantibodies, and thyroid-stimulating hormone levels were normal. Serum IgG titers for Blastomyces dermatitidis, Histoplasma capsulatum, Cryptococcus neoformans, Neospora caninum, and IgG and IgM titers for Toxoplasma gondii were negative.
Lupus erythematous and antinuclear antibody testing were negative. The patient's fresh frozen serum was incubated with normal canine extraocular muscle and staphylococcal protein A conjugated with horseradish peroxidase (SPA-HRPO), then stained for peroxidase localization.1 No labeling of myofiber components was observed. Serology for type 2M myofibers was negative.2, 3 Thoracic radiographs demonstrated no evidence of neoplasia or fungal disease.
ASK YOURSELF ...
What additional diagnostic testing should be pursued?
A. Schirmer's tear test and rose bengal stain
B. Ultrasonography, CT, and muscle biopsy
C. Fluorescein stain and intraocular pressure measurement
D. Conjunctival biopsy
E. Gonioscopy with scleral depression
Correct Answer: B
Ultrasonography, CT, and muscle biopsy
Diagnostic imaging techniques are often useful in the diagnosis of exophthalmos (protrusion of the globe out of the orbit). In this patient, ocular ultrasound revealed markedly swollen extraocular muscles OU (Figure 2) with homogeneous low-reflective enlargement, suggestive of myositis.4-7