Case 2: Facial nerve dysfunction in a mixed-breed dog
An 8-year-old spayed female mixed-breed dog was presented to Red Bank Veterinary Hospital in Tinton Falls, New Jersey, for
evaluation of ocular discharge and conjunctivitis in the right eye.
The dog had initially been evaluated by the referring veterinarian. Treatment had consisted of topical ophthalmic solution
containing a corticosteroid-antibiotic combination (neomycin-polymyxin-dexamethasone). After five days, the signs had failed
to improve, and the dog had been referred to Red Bank Veterinary Hospital.
Physical and neurologic examinations
Physical examination abnormalities were limited to the nervous system. The dog's body condition score was 6/9, subjectively.
No abnormalities were seen on an otoscopic examination.
Neurologic examination revealed bilateral drooping of the lips and drooping of the pinna of the right ear as well as a lack
of palpebral reflex in the right eye. Response to stimulation of the nares was normal bilaterally. The neuroanatomic diagnosis
was consistent with dysfunction of cranial nerve VII (facial nerve).
Differential diagnoses included ischemic infarction, idiopathic facial nerve paralysis, infection such as otitis media, neoplasia,
and trauma. The latter seemed unlikely given the lack of history of any traumatic event.
Initial diagnostic tests
A CBC and serum chemistry profile were performed. The CBC results were normal, and the serum chemistry profile revealed hypercholesterolemia
(440 mg/dl; reference range = 110 to 320 mg/dl).
Based on neurologic deficits and hypercholesterolemia, total T4, free T4, and TSH concentrations were measured. As in the previous case, a triglyceride concentration was not measured.
While pending results of the thyroid function testing, the dog developed a right-sided vestibular ataxia. In addition to the
previous neurologic deficits, neurologic examination at the time of the development of vestibular ataxia revealed normal mentation
and gait, no postural reaction deficits, normal reflexes and tone, and no abnormal nystagmus. The neuroanatomic diagnosis
was consistent with right-sided cranial nerve VIII (vestibulocochlear nerve) as well as cranial nerve VII. Magnetic resonance
imaging (MRI) of the head revealed no abnormalities. Because of this lack of MRI abnormalities and owner preference, a cerebrospinal
fluid analysis was not performed.
Table 4: Case 2 pituitary-thyroid axis testing results
The total T4 and free T4 concentrations were decreased, and the TSH concentration was increased, consistent with primary hypothyroidism (Table 4). However, there is a small possibility that the thyroid gland itself was normal but being suppressed by the corticosteroid
in the ocular preparation that cannot be ruled out. But the elevated TSH concentration makes this possibility less likely.