Page 816 - Clinical Small Animal Internal Medicine

784 Section 8 Neurologic Disease

suggesting selective immunodeficiency in some animals Mycotic Meningoencephalitis
VetBooks.ir contributing to the presence of infection. uncommon in dogs and cats. Small animals with mycotic
Fungal CNS infections other than cryptococcosis are
CNS infections can have neurologic signs that range
Bacterial Meningoencephalitis
Bacterial infection of the CNS is a relatively rare cause of from peracute in onset to insidiously progressive, and
encephalitis and/or meningitis in dogs and cats compared lesion localization is often suggestive of multifocal
with other species. Bacterial infection of the brain can be disease.
the consequence of hematogenous spread (metastasis Cryptococcus neoformans is the most commonly impli-
from distant foci of infection), penetrating injury to the cated systemic mycotic agent causing CNS signs in both
skull (bite wound, bullet, surgery) or direct extension of dogs and cats. Extraneural organ involvement is often
infection from the middle/inner ear, eyes or nasal sinuses. present, but may be clinically occult, or absent in some
Infection of the CNS may result in an abscess and/or, much cases. Brainstem disease resulting in signs of vestibular
less frequently, collection of pus (empyema) in subdural or dysfunction is frequently reported. Peripheral vestibular
epidural locations. Brain abscesses are life threatening due disease has also been reported to be a sequel of crypto-
to systemic and local toxicity (in the early stages of cerebri- coccosis in cats.
tis) and increased intracranial pressure (during/after cap- The diagnosis of cryptococosis is best established
sule formation). Clinical signs are largely the result of the by cytologic or histologic demonstration of the organ-
inflammatory reaction that the bacteria provoke. ism, with its characteristic capsule, from tissue aspi-
Affected animals can present with a wide variety of rates or biopsies, or in body fluids, such as urine or CSF;
neurologic signs of intracranial disease that reflect a organisms can be identified in the CSF of more than
focal anatomic diagnosis suggesting a space‐occupying 90% of dogs with CNS signs. In cases in which organ-
lesion or a multifocal syndrome associated with many isms cannot be demonstrated, serologic testing using
small microabscesses. These signs are usually rapidly the latex agglutination procedure that identifies crypto-
progressive and frequently fatal if left untreated. Fever is coccal capsular antigen is recommended. Serologic
present in approximately 50% of cases at presentation. testing can be performed on blood or CSF, although
Hematology usually reflects an inflammatory process CSF is preferred. Latex agglutination testing is gener-
(leukocytosis with or without left shift) or can be normal. ally considered to be both highly sensitive and specific.
Imaging of the brain (CT or MRI) may be suggestive of CT and MRI imaging of the brain in cats and dogs with
an inflammatory process and may reveal a defect in the cryptococcosis have demonstrated numerous and
skull suggestive of a penetrating injury or signs sugges- variable abnormalities including single or multifocal
tive of otitis media/interna. mass lesions, meningeal enhancement, intraparenchy-
Cerebrospinal fluid analysis usually reveals an elevated mal ring enhancement associated with “punch hole”
nucleated cell count, with the majority of cells being lesions in the gray matter, and choroid plexus
degenerate neutrophils, and marked elevation in total enhancement.
protein concentration. Bacteria may be visible in the spi- The recommended therapy for CNS cryptococcosis is
nal fluid. In some cases, CSF can be normal or may show fluconazole (5 mg/kg PO q12h), as this agent effectively
nonspecific inflammatory changes. CSF should be cul- penetrates CNS tissues. Intrathecal administration of
tured if it contains degenerate neutrophils although it is amphotericin B has also been described. The length of
uncommon for culture to be positive. Urine and blood therapy required is often protracted, and serial serologic
culture should also be considered in animals in which monitoring has been recommended. Treatment should
there is no obvious source of infection. ideally be continued until clinical signs have resolved,
Treatment of abscesses centers around antibiotic ther- CSF analysis has normalized, and two consecutive titers
apy, often for long periods, based on culture and drug performed one month apart have been negative.
sensitivity testing of organisms isolated from the abscess. However, relapses have occurred after consecutively
When cultures cannot be obtained, a broad‐spectrum negative serum titers, and it has been suggested that
antibiotic, such as third‐generation cephalosporins and when possible, treatment should continue until the
enrofloxacin or metronidazole, can be used. In the early patient is seronegative and all previously documented
stages antiinflammatory doses of corticosteroids to intracranial MR abnormalities have resolved. Newer
reduce surrounding edema are indicated, and seizure antifungal agents, such as voriconazole, offer advan-
control with anticonvulsants may be required. Antibiotic tages including excellent CNS penetration, a broader
therapy should be maintained for several weeks after antifungal spectrum, and greater potency than either
clinical signs have resolved. Surgical decompression by fluconazole or itraconazole, and thus may prove to be
craniectomy is indicated in cases of brain abscess that do beneficial for the treatment of CNS cryptococcosis in
not respond to medical management. dogs and cats.