Page 815 - Clinical Small Animal Internal Medicine
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71  Disorders of the Forebrain  783

               Clinical signs most commonly relate to hydrocephalus   Following acute systemic infection in intermediate
  VetBooks.ir  and associated forebrain syndrome (seizures, cortical   hosts in which the organism can be disseminated to
                                                                  many body organs (this phase may be subclinical), tissue
               blindness, obtundation) although central vestibular
               signs are often also reported, as the meningitis caused
                                                                  and heart muscle. The parasites are mainly intracellular
               by FIP may be more severe in the ventral brainstem   cysts form most commonly in the CNS, skeletal muscle,
               and at the base of the cerebellum, and choroid plexitis   and subclinical infection may persist for the life of the
               and ependymitis are frequently severe in the caudal   host, although activation of toxoplasmosis may occur in
               fossa.                                             association with severe immunosuppressive disorders.
                 The diagnosis of FIP is challenging, especially when   These protozoal organisms have the potential to cause
               signs are restricted to the CNS. Hematology findings   an extremely variable number of clinical neurologic syn-
               may include anemia, leukocytosis, and hyperglobuline-  dromes. Two main forms are observed:
               mia. Serum tests for anticoronavirus antibodies have a     encephalomyelitis – neurologic signs associated with
               low specificity and a negative serum titer does not   ●  protozoal encephalomyelitis are variable and may
               exclude the possibility of FIP‐associated neurologic dis-  reflect a focal or multifocal disease process
               ease because soluble antibodies can form immune com-    Neospora myositis‐polyradiculoneuritis – this is prob-
               plexes and escape detection by standard tests. There is   ●  ably the most commonly reported infectious myositis
               also considerable overlap in titers in cats with and with-  in dogs and presents with severe pelvic limb paresis
               out FIP (some cats with FIP have low titers, while many   and skeletal muscle fibrosis in young dogs, especially
               cats with high titers never develop FIP). The CT and MR   those less than six months of age.
               abnormalities present in the brains of cats are well
               described and include meningeal contrast enhancement,   A tentative antemortem diagnosis  of toxoplasmosis  is
               choroid plexitis (contrast enhancement), ependymitis,   established in dogs most commonly through elevated
               granuloma formation, and obstructive hydrocephalus,   IgM titers, IgG seroconversion, or documentation of a
               most commonly due to blockage of the mesencephalic   positive clinical response to an antiprotozoal treatment
               aqueduct. CSF analysis may reveal a predominantly neu-  regimen. In cats, an elevated serum or CSF IgM titer is
               trophilic or mixed cell pleocytosis, but can be normal.   considered  diagnostic  for  toxoplasmosis.  However,  a
               CSF total protein concentration is often markedly ele-  positive titer can be found in animals previously subclin-
               vated (>200 mg/dL). Documentation of elevated corona-  ically infected with either organism and demonstration
               viral antibody concentrations, especially in cerebrospinal   of a rising titer with serial (monthly) testing may be
               fluid, confirms exposure and is supportive of the diagno-  required to confirm a diagnosis of active disease.
               sis. However, this result must be interpreted with respect   Neosporosis is diagnosed by serologic detection of indi-
               to the integrity of the blood–brain barrier. Positive coro-  rect fluorescent antibody titers in dogs. Demonstration
               navirus‐specific PCR performed on CSF can be used as a   of tachyzoites of either organism in various tissues or
               relatively reliable antemortem diagnostic tool.    body fluids is also diagnostic but rarely achieved. CSF
                 Treatment of FIP is immunosuppressive or immu-   analysis typically demonstrates pleocytosis with a mixed
               nomodulatory in nature, but the disease should be   population of neutrophils and the presence of small and
               considered terminal in virtually all affected cats.   large mononuclear cells. Eosinophils may also be seen.
               Corticosteroids, chlorambucil, cyclophosphamide, and   Sensitive PCR assays have been reported for the detec-
               interferons have been used with variable efficacy in FIP   tion of both Neospora caninum DNA and Toxoplasma
               cases.                                             gondii  DNA  in  biological  samples.  Muscle  biopsy  is
                                                                  indicated in dogs with polyneuropathy/polymyositis and
               Protozoal Encephalitis                             may reveal nonsuppurative inflammation and tachy-
               Toxoplasmosis and neosporosis are polysystemic pro-  zoites within myocytes.
               tozoal diseases capable of causing heterogeneous signs   Treatment for both diseases is identical. Clindamycin
               of peripheral and CNS dysfunction. Natural infection   (10–15 mg/kg PO q812h for a minimum of 12 weeks) is
               with Toxoplasma gondii is more common in cats, but   the preferred therapy. However, TMS (15 mg/kg PO
               also occurs in dogs. Ingestion of tissue from infected   q12h) in combination with pyrimethamine (1 mg/kg/day
               intermediate hosts (ingestion of encysted bradyzoites)   PO) may also be effective. Folic acid or brewer’s yeast
               is the most common cause of infection in both species.   supplementation should be considered (5 mg/dog/day)
               Other forms of infection include fecal contamination   in animals receiving this latter therapy. The prognosis for
               and in utero infection. With Neospora caninum, dogs   survival is fair to good, but recovery of neurologic func-
               are affected, most commonly via in utero transmission,   tion may be incomplete in those animals with severe
               although they may also be infected by ingestion of   clinical signs. In the author’s experience, some cases may
               intermediate host tissue.                          require  long‐term  (a  year  or  possibly  longer)  therapy,
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