The Case of the Loopy Shepherd
1. Referral:
“Daisy” is a 5 year old FS Shepherd mix* referred for a sudden onset of blindness. Three days prior to presentation, Daisy started to bump into objects and her behavior became increasingly “loopy.” The morning of referral, a left head tilt was noted, along with an incoordinated gait.
2. Exam:
Neurologic examination revealed dull mentation with agitated behavior. There was a tendency to circle to the left with ataxia of all four limbs. Postural reaction deficits were noted on the left side. Menace response was absent bilaterally with dilated pupils and absent PLR OU. A resting horizontal nystagmus, fast phase to the right, was noted. The remainder of the neurologic examination was normal. Fundic exam revealed a normal retina but enlargement of both optic discs.
3. Neurolocalization:
This case is a great example of a confusing set of neurologic symptoms that actually make a lot of sense upon deeper examination. I find in a case like this that the best approach is to start with the “highly localizing neurosymptoms.” Then I see how many other exam abnormalities I can lump together with these highly localizing findings. For example, in this particular case, the presence of nystagmus means with certainty that the dog has at least a vestibular localization. Since the fast phase of the nystagmus is to the right, we know the vestibular lesion is probably on the left. Therefore, the ataxia and circling to the left can be accounted for by the left vestibular localization. Left sided postural reaction deficits suggest a central vestibular lesion. Now we have successfully explained half of our neurologic symptoms and can consider the remaining symptoms.
Blindness could either be post-chiasmic (cortical) or chiasmic/pre-chiasmic (eye or optic nerves). The behavior change in this dog immediately brings up concern that the blindness is cortical in nature, so we should next ask ourselves what we would expect on the remainder of the neuro-ophthalmologic examination in the case of cortical blindness. The answer is normal pupil size and normal PLR’s. However, in this case we have dilated pupils and absent PLRs. The only possible localization for these findings is a pre-chiasmic lesion. On the fundic examination, we can visualize disease of the optic nerves. Therefore, we now have a second localization to the optic nerves bilaterally, meaning this dog has multifocal CNS disease.
So the only symptoms left to explain are the behavior changes and dull mentation. These could be simply a consequence of sudden vision loss, but the magnitude of the behavior change and the presence of aggression raise the possibility that there is an intracranial cause of these symptoms, which would go along with our overall multifocal localization.
4. Procedures:
Brain MRI revealed patchy, multifocal contrast-enhancing lesions of the left brainstem, central diencephalon, and both optic nerves. CSF white blood cell count was markedly elevated at 512/uL (normal <4/uL) with a predominance of mononuclear cells on cytology. Infectious titers were negative.
5. Diagnosis:
Immune-mediated encephalitis (i.e. Granulomatous Meningoencephalitis)
6. Outcome:
Daisy responded to long-term immunosuppressive therapy with prednisone and returned to normal except for partial visual deficit OD. Eighteen months after prednisone was discontinued, Daisy re-presented for dilated pupils OU. Immunosuppression was re-instituted and Daisy returned to her old self.
7. Discussion:
Daisy’s case is a good example of how anyone can approach a more complicated set of symptoms and still work through to the correct localization. My advice is always to focus on the symptoms that are highly localizing and then to see how many other symptoms can be explained by this localization. Animal Specialty Group will be putting together a continuing education program focusing on neurology for the general practitioner on October 6, 2011. I will be expanding on this concept, giving a more comprehensive list of what I call “highly localizing neurosymptoms” and working through the neurolocalization on both simple and complicated cases. Save the date, I look forward to seeing you all there!
by Stacey A. Sullivan, DVM,
Diplomate ACVIM (Neurology)
*Photo of German Shepherd is not “Daisy.”
