Comparative Neuromuscular Laboratory

NEUROMUSCULAR CASE OF THE MONTH – OCTOBER 2007

Chronic pain opening the jaw and bilateral enophthamos in an 8 year old FS Rottweiler
Contributed by Dr. Lynelle Johnson
Veterinary Medical Teaching Hospital
University of California, Davis

Clinical History
This 8 year old FS Rottweiler had a 1.5 year history of intermittent mucoid to hemorrhaghic right sided nasal discharge with reverse sneezing and a 6 week history of enophthalmos and lethargy. At this time, an otoscopic examination was normal, and rhinoscopy with biopsy revealed a lymphoplasmacytic inflammation with marked submucosal edema. No improvement was noted with prednisone treatment. Three months later an MRI performed at an imaging center showed exudative material suspicious for fungal granuloma in the right frontal sinus. Fourteen months later the dog presented to the UC Davis Veterinary Medical Teaching Hospital for pain opening the jaw and bilateral enophthalmos.

Physical Examination
The predominant abnormality on physical examination was bilateral enophthalmos and third eyelid protrusion (see image above) with the right eye not visible to assess the pupil. Neurologic examination revealed depressed mentation. No specific abnormalities were identified in other body systems. Differential diagnosis at this time included Horner’s syndrome, chronic atrophic masticatory muscle myositis affecting predominantly the pterygoid muscles, a cranial neuropathy, or space occupying fungal infection or neoplasia.

Diagnostic Tests
CBC and chemistry panel including serum creatine kinase activity, and urinalysis - within the reference range
Serologic testing for antibodies against masticatory muscle type 2M fibers (masticatory muscle myositis) - negative
Serology for Aspergillus antibody – negative
Ophthalmology examination – Pharmacologic testing with a direct acting sympathomimetic did not resolve the enophthalmos making a Horner’s syndrome less likely. The eye is normally held forward within the orbit by smooth muscles within the periocular/periorbital tissue, which are innervated by branches of sympathetic nerves from the cranial cervical ganglion.
Thoracic radiographs – no abnormalities detected

Magnetic Resonance Imaging (MRI)
An MRI with contrast (see images below) revealed a large complex soft tissue mass lesion centered at the right frontal sinus and invading the left. There was destruction of the inner table of the frontal sinuses bilaterally, the right frontal bone, the cribriform plate, and the right lateral aspects of the palatine and sphenoid bones. Extension of the lesion into the right retrobulbar space was suspected. These lesions were most consistent with severe and extensive fungal disease although neoplasia could not be ruled out. Trephine biopsies of the sinus just revealed bony lysis. Fungal cultures were negative.

Conclusion
Since a fungal infection was considered most likely, the dog was sent home on voriconazole (200 mg/kg PO BID) with the hope of stalling progression of disease. After no response, the dog was euthanized due to progression of disease and a necropsy performed. The most significant finding was right-sided nasal squamous cell carcinoma with invasion into the calvarium and into the right frontal cerebral cortex. The author thanks Dr. Peter Dickinson (neurology), Dr. Seth Eaton (ophthalmology), Dr. Sarah Puchalski (radiology), and Dr. Jim MacLachlan (pathology) for assistance with this case.