Page 1152 - Small Animal Internal Medicine, 6th Edition

1124 PART IX Nervous System and Neuromuscular Disorders

spinal cord compression by an epidural abscess, surgery may
be required.
VetBooks.ir are common, particularly if the underlying source of the
The response to antibiotic therapy is variable, and relapses
bacterial infection cannot be resolved. The prognosis should
be considered guarded in most cases, because even with
appropriate therapy many animals die. An exception may be
otogenic intracranial infections in dogs and cats, where a
good success rate after treatment with surgical drainage and
antibiotics has been reported.
CANINE DISTEMPER VIRUS

A Canine distemper virus (CDV) is a paramyxovirus that
affects the CNS of dogs. Widespread vaccination has sub-
stantially decreased the incidence of clinically apparent CDV
infections in many regions, but outbreaks still occur among
unvaccinated dogs and sporadically in vaccinated dogs.
Clinical signs vary depending on virulence of the virus
strain, environmental conditions, and host age and immune
status. Most CDV infections are probably subclinical or
are associated with mild signs of upper respiratory tract
infection that resolve without therapy. Young, immuno-
compromised, and unvaccinated dogs are most likely to
develop severe generalized distemper.
Progressive generalized infection with CDV most com-
B monly affects unvaccinated puppies between 12 and 16
weeks of age. The first sign of infection is a mild serous to
mucopurulent ocular and nasal discharge followed by a dry
FIG 64.3
(A) This 4-year-old Cocker Spaniel with a chronic cough and sometimes tonsillitis. The cough becomes moist
retrobulbar abscess developed fever and severe depression. and productive as pneumonia develops. Affected dogs are
(B) Cerebrospinal fluid from the dog revealed septic depressed, inappetent, and often febrile. Diarrhea develops
inflammation. Postmortem examination confirmed in some puppies and may be mild or severe. Hyperkeratosis
communication between the retrobulbar abscess and central of the footpads and nose, pustular dermatitis affecting the
nervous system. unhaired skin on the ventral abdomen, and severe moist
otitis externa may also be seen. Neurologic signs typically
begin 1 to 3 weeks after recovery from the initial systemic
gram-negative infections, and metronidazole can be used for illness and may include forebrain, vestibulocerebellar, brain-
anaerobic infections. Doxycycline, trimethoprim-sulfa, and stem, or spinal cord signs. Some of the most common neu-
chloramphenicol may also reach therapeutic concentrations rologic signs reported include dementia, disorientation,
in the CNS. While inflammation persists, ampicillin and altered mentation, seizures, circling, head tilt, nystagmus,
amoxicillin with clavulanic acid are also effective and may cranial nerve deficits, hypermetria, tetraparesis, and ataxia.
be the best choice for gram-positive infections. Initial treat- Seizures can be of any type, depending on the region of the
ment with a combination of intravenous (IV) ampicillin forebrain that is affected, but “chewing gum” seizures caused
(22 mg/kg IV q6h), enrofloxacin (2.5 mg/kg IV q12h), and by polioencephalomalacia of the temporal lobes are com-
metronidazole (15 mg/kg IV × 1, then 7.5 mg/kg IV q8h) monly described. Myoclonus, a repetitive rhythmic contrac-
may be warranted if the infectious agent is unknown. When- tion of a group of muscles resulting in repetitive flexion of a
ever possible, antibiotics should be administered intrave- limb or contractions of the muscles of mastication, is often
nously for 3 to 5 days to achieve high CSF concentrations, referred to as distemper chorea and is very common in dogs
and then oral therapy should be continued for 4 to 8 weeks with distemper encephalomyelitis. Anterior uveitis, optic
after recovery. Concurrent IV fluids and systemic support neuritis, or chorioretinitis may be detected during an oph-
are important, and anticonvulsants should be administered thalmologic examination in some infected dogs. Dogs sur-
to patients having seizures (see discussion of status epilepti- viving mild CDV infection before eruption of their
cus in Chapter 62). Antiinflammatory drugs or glucocorti- permanent teeth will often have irregular dental surfaces and
coids (dexamethasone, 0.2 mg/kg IV q12h) are sometimes brown discoloration of their teeth subsequent to virus-
administered for the first 2 days of antibiotic treatment to induced enamel hypoplasia. Older animals occasionally
minimize the inflammatory consequences of antibiotic- develop chronic encephalomyelitis months to years after
induced bacterial lysis. When imaging reveals significant prior CDV infection and recovery (old dog encephalitis),