Page 808 - Problem-Based Feline Medicine

800 PART 10 CAT WITH SIGNS OF NEUROLOGICAL DISEASE

● Impaired facial sensation is detected by decreased Pathogenesis
head withdrawal when the contralateral nasal sep-
Likely symptomatic epilepsy is common in cats.
tum, upper lip or whiskers are touched.
It is most often caused by an acquired focal thalamo-
Large or diffuse forebrain lesions (e.g. tumors, edema)
cortical lesion that is no longer active but has trans-
may cause signs of increased intracranial pressure
formed into an epileptic focus by irritating the
(e.g. marked depression, bilateral miosis); this may
surrounding neurons.
evolve to tentorial herniation with signs of brainstem
● Following an insult to the brain such as trauma,
compression (e.g. coma, unresponsive mydriasis, abnor-
encephalitis or ischemia, the glial reaction may result
mal respiratory patterns and death by respiratory arrest).
in a persistent glial focus, which irritates the sur-
rounding neurons.
WHAT? ● Seizure onset is usually delayed by a few to several
months from an initial brain insult. The insult
Most cats with seizures have a structural forebrain may have occurred in utero (e.g. porencephalic
lesion that may be active (e.g. encephalitis, tumor, [cystic] lesions due to fetal encephalitis), at birth
ischemic encephalopathy) or inactive (e.g. post- (e.g. dystocia-related cerebrovascular accidents) or
ischemic glial scar). Extracranial causes of seizures later in life at any age. Post-natal diseases may have
(e.g. metabolic, toxic) and idiopathic epilepsy are rare. been symptomatic (e.g. encephalitis, ischemic
encephalopathy, head trauma) or asymptomatic
Compulsive circling may be caused by lesions affect-
(e.g. atypical form of ischemic encephalopathy,
ing the rostral thalamus or frontal lobe and is usually
non-suppurative meningoencephalitis).
toward the side of the lesion. Most common causes are
● Symptomatic seizures occurring during the active
neoplasia, trauma and ischemic encephalopathy.
phase of a cerebral disease may or may not lead to
Personality and behavioral changes result from lesions likely symptomatic epilepsy, depending on the
affecting the limbic system and associated areas of extent of secondary gliosis.
frontal and temporal lobes. Most common causes are neo-
Other rare congenital or inherited focal cerebral
plasia, trauma, ischemic encephalopathy, feline infectious
anomalies may also act as epileptic foci. These include
peritonitis and hepatic encephalopathy.
lesions associated with surrounding gliosis (e.g. vascu-
Diagnosis is based on history, clinical examinations, lar malformations such as angiomas and arteriovenous
CSF analysis (reference values in cats are a protein malformations) or with intrinsic neuronal hyper-
concentration ≤ 0.36 g/L (0.036 mg/dl) and a leukocyte excitability (e.g. disorders of neuronal migration such
9
count ≤ 0.002 cells/10 (2/μl) with the majority of cells as cortical dysplasia and heterotopias).
being mononuclear cells), brain imaging and other ● Seizures usually start during adolescence or young
ancillary tests. adulthood.

DISEASES CAUSING SEIZURES, Clinical signs
CIRCLING AND/OR CHANGED
The initial seizure frequency usually is low with single
BEHAVIOR
seizures occurring at intervals of several weeks to
months. The subsequent seizure frequency often
LIKELY SYMPTOMATIC EPILEPSY*** remains low but may progressively increase over
months or years due to a self-perpetuating electrical
Classical signs kindling-like phenomenon. This sometimes leads to
intractable seizures with frequent and severe cluster
● Recurrent seizures are the only problem.
seizures and status epilepticus.
● The initial seizure frequency is low but
may increase over time. Seizures are partial (focal) with or without secondary
● Seizures are partial in onset with or generalization. Secondary generalization may some-
without secondary generalization. times occur so quickly that no features of partial
seizures may be detected clinically.