Page 829 - Clinical Small Animal Internal Medicine

73 Meningoencephalitis and Meningomyelitis 797

dogs have no known infectious etiologies, and are likely with ataxia and paresis of all four limbs. Myelitis also
VetBooks.ir immune‐mediated processes that occur in individuals results in ataxia and paresis, together with spinal pain
and possibly deficits in segmental spinal reflexes.
with a genetic predisposition after some sort of antigenic
“trigger.” Such triggers remain unknown at this time but
any of these regions. One hallmark of inflammatory
might be related to exposure to environmental antigens Postural reaction deficits may be seen with lesions in
or to antigens from infectious agents not involving the disease of the CNS is that it frequently results in a
CNS (e.g., respiratory or gastrointestinal infection). multifocal distribution of signs (i.e., multifocal lesion
localization), which is uncommonly seen with other
disease processes.
Signalment Occasionally, signs that are very characteristic for a
specific disease may be noted, such as distemper
Although dogs and cats of any age or breed can be affected “myoclonus” or rigid limb extension due to muscle
by inflammatory CNS disease, certain populations are contractures in dogs with Neospora caninum infection.
predisposed to its development. Infectious diseases In addition, some infectious diseases may involve mul-
occur more frequently in younger animals, which may be tiple organ systems, producing signs referable to the
related in part to maturation of the immune system or respiratory system (e.g., canine distemper, blastomycosis),
vaccination failures. As mentioned above and detailed in bone (Coccidioides immitis), integument (canine distem-
Table 73.2, many of the apparent noninfectious canine per, blastomycosis), gastrointestinal tract (canine dis-
meningoencephalitides have strong breed predisposi- temper, Prototheca) or other systems. Involvement of
tions, and these diseases also have fairly consistent ages other systems is not typical for the “sterile” meningoen-
of onset. As a general rule, meningoencephalitis occurs cephalitides, although occasionally polyarthritis is seen
more frequently in young to middle‐aged animals. in dogs with SRMA.
Gender seems to play a minor role in most of these dis-
eases, although some early reports of GME and a more
recent study of NME have described a female predomi- Diagnosis
nance. In contrast, most of the dogs reported to develop
eosinophilic meningoencephalitis have been male. A complete blood count may show abnormalities with
certain infectious agents, such as thrombocytopenia
with rickettsial infections or eosinophilia with some
parasite or protozoal diseases. If CNS inflammation is
History and Clinical Signs part of a multisystemic infectious or inflammatory pro-
cess, then a neutrophilic or monocytic leukocytosis may
The history may reveal important predisposing factors be evident. Serum chemistry may similarly show abnor-
for some of the infectious diseases, including vaccination malities in certain conditions such as hyperglobulinemia
history, exposure to ticks or mosquitoes, animal bites, with FIP or Ehrlichia canis infections or changes indica-
ingestion of raw food or carrion, and exposure to soil or tive of renal or hepatic dysfunction in multisystemic
stagnant water. Obtaining a thorough travel history may infections. However, in most animals with inflammatory
elucidate additional potential differential diagnoses as CNS disease, the complete blood count (CBC), serum
some of the tick‐borne and fungal diseases have clear chemistry, and urinalysis are relatively unremarkable.
geographic distributions. Although infrequently analyzed, acute phase proteins
Clinical signs of meningoencephalitis and meningo- may show changes in some animals, such as elevations in
myelitis typically have an acute onset with progression serum C‐reactive protein, fibrinogen or serum amyloid
over time; chronic infection or inflammation of the CNS A protein.
is unusual. The signs seen are dependent on the region A diagnosis of meningoencephalitis or meningomyeli-
of the nervous system that is involved. Animals with tis is most commonly made with advanced diagnostic
meningitis (including SRMA) typically present for pain, imaging and analysis of CSF. Conventional imaging tests
particularly cervical pain, and neurologic deficits are such as radiography or ultrasound have little role in the
frequently absent or subtle. Patients with forebrain diagnostic process outside of screening other organs
involvement may present with seizures, altered menta- within the thoracic and abdominal cavities for disease.
tion, depressed consciousness, visual deficits, and com- Myelography is a technique that involves the injection of
pulsive pacing or circling. Brainstem disease can result contrast material into the subarachnoid space, fol-
in cranial nerve deficits such as vestibular dysfunction, lowed by radiography of the vertebral column.
facial nerve paralysis, pupillary abnormalities, strabismus, Interruptions in the flow of contrast material can result
dysphagia, megaesophagus or tongue atrophy together in several imaging patterns indicating mass lesions in