Page 822 - Clinical Small Animal Internal Medicine

790 Section 8 Neurologic Disease

cranial nerves is typically due to brainstem involve­ Etiology
VetBooks.ir ment where the cranial nerve nuclei are situated and To ensure a complete list of differential diagnoses,
there may also be concurrent mentation changes due
to the diffuse projections of the reticular activating
system (RAS) in this location. breaking down differentials into larger categories and
then fitting specific differentials into those categories
Cerebrothalamic dysfunction – mentation changes,
● will help limit oversights.
seizures, head turn +/− wide circles, visual deficits,
proprioceptive deficits, etc. Signs are due to multifo­ ● Degenerative
cal/diffuse disease or increased intracranial ● Anomalous/congenital
pressure. ● Metabolic
Cerebellar signs – intention tremors, hypermetria, ● Neoplasia, nutritional
●
truncal sway, absent menace with intact vision. ● Infectious, inflammatory, idiopathic, iatrogenic
Cerebellar lesions produce ipsilateral signs (or bilateral ● Toxic, traumatic
if diffuse/multifocal cerebellar involvement). ● Vascular – hemorrhagic or ischemic
Proprioceptive deficits +/− paresis – proprioceptive
● In general, acute versus chronic history should help
deficits may come from a lesion interrupting the flow with ranking differentials. Acute histories are more com­
of information anywhere along the pathway from the monly associated with idiopathic disease, vascular
cortex through the thalamus and brainstem (which events (ischemic vs hemorrhagic), toxin exposure (met­
may result in varying degrees of paresis) or from the ronidazole, ronidazole) +/− otitis interna (usually
cerebellum (no paresis). with an associated chronic otitis externa/media).
Thiamine deficiency is often acute and can progress
The presence of one or more of the above signs, by defi­ rapidly in cats. Of course, there are always exceptions.
nition, localizes the problem to the CNS. Central disease
may be due to a multifocal problem (i.e., infections, Peripheral Vestibular Disease
inflammatory disease, lymphoma, multiple metastatic
lesions), from increased ICP leading to compression of Anomalous/Congenital
adjacent vestibular structures, or from direct involve­ Some animals are born with signs of peripheral ves­
ment of the central vestibular system. tibular disease, either unilateral or bilateral. Bilaterally
Examination of the vestibular patient can be challeng­ affected animals are commonly deaf as well. The exact
ing, making localization difficult. For example, patients cause is unknown, although both degeneration of the
that are profoundly affected by nausea and imbalance vestibular nerve and inflammation of the labyrinth
often feel/act mentally dull and lethargic. Supporting have been described. Recent research suggests a possible
patients to assess proprioception can be futile when they genetic mutation in a doberman puppy. The signs are
are rolling and flailing. Finally, it is important to consider often noted when the animal first becomes mobile. Head
any preexisting disease that may suggest two localiza­ tilt and ataxia, +/− circling are seen. Bilaterally affected
tions or multifocal disease, such as a history of cervical animals may look more “cerebellar,” swinging the head
pain or seizures. back and forth, and have a more generalized appear­
Nystagmus has been classically used to localize ves­ ance to the ataxia. Often pathological nystagmus is not
tibular disease as peripheral versus central, but this appreciated and physiological nystagmus is frequently
should be undertaken with caution. Vertical nystagmus decreased/absent in these bilaterally affected patients.
is strongly suggestive of, but not definitive for, central Most animals will remain static or improve with time,
disease. Constant, unchanging horizontal nystagmus is but deafness is typically permanent. Congenital ves­
associated with peripheral disease. tibular disease and deafness are possible in any breed,
Paradoxical vestibular disease is associated with but reported breeds include Siamese, Burmese, and
lesions in the rostral and medial vestibular nuclei, the Tonkinese cats, Dobermans, cocker spaniels, akitas,
caudal cerebellar peduncle, or the flocculonodular lobe German shepherds, beagles, and smooth fox terriers.
of the cerebellum, and therefore it is always central in Primary secretory otitis media is a disease most com­
origin. Lesions associated with any of these neuroana­ monly seen in Cavalier King Charles Spaniels and less
tomic localizations should produce lateralizing signs. commonly in other brachycephalic breeds, such as
Once the side is determined (i.e., side of proprioceptive french bulldogs. It results in a collection of mucoid effu­
deficits, hypermetria), if the head tilt/circling is away sion in the tympanic bulla presumably due to these
from the lesion, +/− the fast phase of the nystagmus breeds extreme nasopharyngeal confirmation compro­
towards the lesion, then it is considered paradoxical ves­ mising normal drainage. It is rarely associated with ves­
tibular disease. tibular signs.