| The same structural anomalies of the brain as described for large animals (see above) are also found in small animals. |
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Hydranencephaly has been described mainly in kittens after in utero exposure to feline panleukopenia virus/parvovirus (
Feline Panleukopenia: Introduction). Brain stem malformations and cerebellar hypoplasia may be seen concomitantly. |
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Hydrocephalus is most common in dogs, particularly in toy and brachycephalic breeds. It can be classified as communicating (nonobstructive), in which CSF can flow freely into the subarachnoid space, or noncommunicating (obstructive). Known causes of noncommunicating hydrocephalus include atresia of the mesencephalic aqueduct, perinatal encephalitis, or adhesions caused by intraventricular hemorrhage at birth. Clinical signs of hydrocephalus usually indicate cerebral
dysfunction and often progress, although some animals may remain asymptomatic. The fontanelles are often patent, and affected animals may have ventrolateral strabismus. Blindness due to polymicrogyria (excessive number of smaller gyri) and asymmetric dilatations of the lateral ventricles have been described in Standard Poodles. Hydrocephalus has been observed in Saint Bernard puppies in association with aphakia (absence of the lens) and multiple ocular defects. Imaging by
ultrasonography (through the fontanelle), computed tomography, or MRI can provide the diagnosis, and CSF analysis should identify encephalitis. Treatment relies on either corticosteroids or surgery to shunt CSF into the peritoneum. |
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Lissencephaly, an absence or reduction of cerebral gyri, is a rare disorder that is seen in Lhasa Apsos. It is also seen in association with cerebellar hypoplasia in Irish Setters, Wirehaired Fox Terriers, and Samoyeds and in Korat cats with microencephaly. The clinical signs of lissencephaly consist of mild behavioral abnormalities and seizures. |
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Pug encephalitis is an ultimately fatal disease that may have a familial basis. Dogs show behavioral changes, seizures, and CSF pleocytosis. A similar nonsuppurative, necrotizing encephalitis has been reported in both Yorkshire Terriers and Maltese Terriers. |
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Idiopathic epilepsy may be inherited in certain breeds, including Beagles, Keeshonden, Irish Setters, Belgian Tervurens, Siberian Huskies, Springer Spaniels, Labrador Retrievers, Golden Retrievers, and German Shepherds. A specific type of seizure known as
temporal lobe epilepsy appears to be familial in Cavalier King Charles Spaniels and is characterized by behavioral manifestations such as fly biting. The diagnosis of idiopathic epilepsy depends on eliminating other causes of seizures, particularly structural brain abnormalities (such as hydrocephalus), encephalitis, or metabolic causes (such as hepatic encephalopathy). |
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Hepatic encephalopathy is usually caused by a congenital portosystemic shunt. The shunt may be a single large vessel, or there may be microscopic shunting of blood within the liver. Breeds often affected include Miniature Schnauzers, Yorkshire Terriers, Cairn Terriers, Australian Cattle Dogs, Old English Sheepdogs, and Maltese Terriers. The clinical signs are usually noticed before 6 mo of age and primarily reflect cerebral dysfunction, including staring into space,
inappropriate vocalizing, aggression, and agitation. Advanced neurologic alterations can cause depression, blindness, myoclonus, stupor, coma, or seizures. In cats, these signs are often accompanied by excessive salivation. A rare cause of hepatic encephalopathy is a deficiency of hepatic urea cycle enzymes. Diagnosis may be facilitated by use of radiographic imaging techniques, such as positive contrast portography, computed tomography, transcolonic portal scintigraphy, or
diagnostic gray-scale ultrasonography. |
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Lysosomal storage disorders that commonly cause seizures include ceroid lipofuscinosis and fucosidosis (see
multifocal disorders, ). |
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Puppy hypoglycemia is an idiopathic syndrome in toy breeds of dogs that is seen in the first 6 mo of life. It seems to relate to a relative immaturity of the liver and can usually be managed by providing frequent meals of a commercial puppy diet. The problem usually resolves as the animal matures. |
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Narcolepsy or cataplexy is inherited in Doberman Pinschers, Labrador Retrievers, and Dachshunds and has been described in additional canine breeds. It is rare in cats. It must be differentiated from various types of syncope. Physostigmine (0.025-0.1 mg/kg, IV) potentiates the frequency and severity of cataleptic attacks. Imipramine (0.5-1.0 mg/kg, PO, tid) can be used to control the severity of the cataplexy. |
