Page 1181 - Problem-Based Feline Medicine

57 – THE BLIND CAT OR CAT WITH RETINAL DISEASE 1173

resultant local hypersensitivity, antibody, and immune- The classical ocular sign suggesting toxoplasmosis is
complex reactions, or whether the eye is secondarily anterior uveitis. The eye(s) may appear cloudy with
involved from reactions occurring in tissues outside hypopyon and keratic precipitates, or have evidence of
the eye. mild uveitis with lymphocytic/plasmocytic nodules in
the iris.
Ocular toxoplasmosis in humans causes a posterior
uveitis, with a necrotizing chorio-retinitis. In cats, the Serological tests have varying degrees of sensitivity
most common presenting sign is anterior uveitis, and and specificity:
in cases with disseminated disease, chorioretinitis and ● Measurement of antibodies may be via indirect
optic neuritis may be seen. fluorescent antibody tests (IFA), indirect hemagglu-
tination tests (IHA), or enzyme-linked immunosor-
Histologically, ocular lesions in cats appear as
bent assay (ELISA). The ELISA test is available in
granulomatous to lymphocytic/plasmocytic, multifocal
kit form, which is a quantitative test and does not
chorioretinitis and/or iridocyclitis.
yield a titer.
● Demonstration of a rise in IgM titers (often meas-
Clinical signs ured by IFA) from paired samples taken 2–4 weeks
apart, indicates a recent active infection. However,
The most common ocular presenting sign is anterior
some cats do not develop detectable IgM titers, and
uveitis, appearing as a cloudy eye. This may be uni-
in other cats, positive IgM titers can persist for
lateral or bilateral.
months to years after infection.
● Affected eyes appear cloudy in acute cases, and
may show hypopyon (pus in the anterior chamber) Polymerase chain reaction (PCR) testing for parasite
and keratic precipitates, which are focal accumu- DNA in tissue or fluid samples. The specificity for
lations of protein, and white blood cells on the active infection is improved when combined with the
corneal endothelium. IgM titer.
Cats that present with lymphocytic, plasmocytic nod- Comparison of levels of aqueous humor T. gondii
ules on the iris, seen as diffuse focal grayish nodules antibody levels with serum levels (Goldman–Witmer
protruding from the anterior iris surface, may have ocu- coefficient or C-value) has been advocated to deter-
lar toxoplasmosis. mine that anterior uveitis has been caused by T. gondii,
although the use of C-values is still controversial. The
Blind cats with toxoplasmosis have chorioretinitis.
Goldman–Witmer coefficient compares the T. gondii-
This is seen as small, multifocal, raised areas in the
specific immunoglobulin concentration with the total
retina that have pigment changes. These cats may also
immunoglobulin concentration in serum and aqueous
have optic neuritis, with an inflamed optic disc that is
humor. A T. gondii-specific antibody C-value > 1 in aque-
hyperemic and raised.
ous humor indicates possible local production, rather
Systemic signs of toxoplasmosis in cats include: than leakage from the serum through a faulty
● Fever, weight loss and muscle pain. blood–ocular barrier. T. gondii-specific C values > 3 are
● Respiratory disease, especially pneumonia. advocated as criteria for evidence of local antibody
● Multifocal neurologic disease. production.
● Liver disease.
● Systemic signs of toxoplasmosis are very rare in adult
Differential diagnosis
cats. They are most common in perinatal kittens.
Differential diagnoses include other conditions that
present as anterior uveitis.
Diagnosis
● Cats with FIP present with anterior uveitis
It is very difficult to make a definitive diagnosis with (hypopyon and keratic precipitates). This is not
demonstration of the organism in cases with T. gondii as common in many geographical areas, and most
infection. A tentative diagnosis is usually made based commonly occurs in young cats from 6 months to
on the clinical signs, supported with laboratory tests. 1 year of age. Currently, there is no definitive test