UVEITIS IN A CAT

History

A small, nine month old, female entire, common domestic shorthair cat presented with blepharospasm and discomfort in the left eye. The owner also reported an episode of discomfort in the right eye two weeks previously, which resolved over a few days with no treatment. The cat was 100% housebound but had been sourced as a kitten from a rescue organisation.

Examination

A full clinical examination was carried out and an ophthalmic examination was carried out as per Appendix 1. Clinical examination was unremarkable. All relevant findings are recorded below.

OD: - Ophthalmic examination unremarkable

OS: - Moderate blepharospasm

- Moderate aqueous flare

- Obvious ventral keratic precipitates (fig. 35)

- Mild dyscoria temperolaterally

- Rubeosis iridis temperolaterally associated with iris thickening (fig. 36)

- Subtle anisocoria OS < OD

STT L = 20mm/minute, R = 22mm /minute

IOP L = 8 mmHg, R= 15 mmHg

Figure 35: On presentation, note ventral keratic precipitates in left eye.

Figure 36: On presentation, note rubeosis iridis at 2 o'clock.

Diagnosis

Anterior uveitis:

- Idiopathic

- Infectious: FIV, FeLV, FIP, Toxoplasma gondii, Bartonella felis, fungal

- Neoplastic: lymphoma, melanoma, other

- Trauma

- Lens induced

Further tests

FIV/ FeLV- serology

FIP - serology and protein profile

Routine haematology and biochemistry profiles

Chest radiographs

Toxoplasma gondii titre

Initial Treatment

Pred Forte QID OD

Meloxicam (Metacam, Boehringer) 2 drops/cat SID PO

Clindamycin (Clindacyl, Vetoquinol) 20 mg/kg BID PO planned for 3 weeks

Laboratory Results

FIV / FeLV seronegative Haematology and biochemistry - unremarkable

Chest radiography - unremarkable

Toxoplasma titre - negative

FIP titre - 80

Albumin/Globulin ratio - 0.81

Alpha-1 AGP - 200

Treatment

Once the Toxoplasma titre had been shown to be negative the clindamycin was stopped after 7 days, i.e. it was used as a systemic antibiotic rather than a specific treatment for toxoplasmosis. The meloxicam was continued for 10 days once daily then decreased to every other day. The Pred Forte was tapered off after 10 days over the following 3 weeks. All treatment was stopped then as the uveitis had resolved.

Discussion

Anterior uveitis is associated with a wide range of possible causes, however the tests available to narrow down the list of potential diagnoses have their pitfalls.

In this case there had been no history of trauma and its lifestyle made this unlikely. It did not come into contact with other cats making a corneal penetration and/ or lens damage again unlikely. There was also no evidence of this within the eye upon examination of the lens.

The history of a sore contralateral eye previously suggested a bilateral or systemic disease but the right eye was healthy when examined. Although the cat was a sexually mature entire it had not had the opportunity for sexual contact due to its house cat lifestyle. It had, however, come from a rescue organisation as a kitten so it was important to rule out FIV/ FeLV infection in the diagnostic process.

The very focal thickened, inflamed area of the iris allowed some suspicion of neoplasia, specifically lymphoma or less likely melanoma. Had the response to treatment been inadequate then aqueocentesis and cytology may have been helpful as lymphoma especially will exfoliate into the surrounding fluid (1).

Two of the most common specific causes of feline uveitis are FIP and Toxoplasma gondii. Both of these are very difficult to definitively diagnose using the tests commonly available. FIP is thought to be caused by a virulent strain of feline corona virus (FCoV) after mutation within the affected cat (2). Unfortunately our present serology testing only gives titres to non specific coronaviruses so cannot distinguish between these two strains. FIP occurs mainly in younger animals and FCoV is known to cause mild diarrhoea in kittens. The majority of FCoV affected cats clear the virus though remaining seropositive so FCoV titres have to be interpreted in the light of clinical signs and corollary diagnostic aids (3).

Ocular clinical signs can occur in either the "wet" or "dry" forms of FIP, although are more commonly associated with the dry form (4). The gold standard of FIP diagnosis is biopsy of the affected tissue, which is not practicable in the eye, or post mortem examination. Although this cat was positive for FCoV the titre was low for dry FIP and the supporting evidence in the form of an albumin:globulin ratio less than 0.4 and an alpha 1 AGP level greater than 1500 micrograms/ml were absent.

Toxoplasmosis is usually acquired by cats through hunting and eating affected animals or occasionally transplacentally. Ocular signs associated with toxoplasmosis are due to damage by the emerging bradyzoites as well as the host's inflammatory response. Demonstration of bradyzoites in ocular tissue (the gold standard of diagnosis) has proven difficult and it has been suggested (5) that the majority of the damage is due to the immune response not the organism itself. Diagnosis is usually made by examining IgG and IgM antibody levels to Toxoplasma however there is a high seroprevalence in normal cats and IgG levels can remain elevated for up to two years post exposure (IgM for three months)(6). Diagnosis can be supported by comparing aqueous humour antibody levels to serum antibody levels (Witmer - Goldmann coefficients) however aqueocentesis is very invasive and has a high potential complication rate. In this case, due to the unreliability of available testing it was decided to treat the disease rather than pursue its diagnosis. Once the IgG titre was shown to be negative treatment was discontinued.

The most common form of uveitis in the cat is idiopathic, nearly 50% in one study (7). The diagnosis of idiopathic uveitis in this case was made on the grounds of negativity to FIV, FeLV, FIP, Toxoplasma and no other signs of concurrent systemic disease. Idiopathic disease can be uni- or bilateral so this is not helpful in diagnosis. Idiopathic uveitis was seen to occur mainly in older cats and a decrease in the immune response along with a greater opportunity for antigen exposure have been mooted to explain this distribution. It may be that the true cause of "idiopathic" uveitis has not yet been found or that it is an immune mediated disease leading older animals to be predisposed.

This cat responded well to treatment, has had no recurrence of ocular disease in the three years of follow up and has remained systemically well.

References

1. Gwin RM, Gelatt KN, Williams LW (1982) Ophthalmic Neoplasms in the Dog. Journal of the American Animal Hospital Association 18, 853-866.

2. Gunn-Moore D, Addie D (2001) The peritoneal cavity. In: BSAVA Manual of Canine and Feline Infectious Diseases, 151-166.

3. Sparkes AH, Gruffydd-Jones TJ, Harbour DA (1984) An appraisal of the value of laboratory tests in the diagnosis of feline infectious peritonitis. Journal of the American Animal Hospital Association 30, 345-350.

4. Andrew SE (2000) Feline infectious peritonitis. Veterinary Clinics of North America: Small Animal Practice, Vol. 30, No 5, 987-1000.

5. Davidson MG, English RV (1998) Feline ocular toxoplasmosis. Veterinary Ophthalmolgy 1, 71-80.

6. Lappin MR, Marks A, Greene CE, Collins JK, Carman J, Reif JS, Powell CC (1992) Serologic prevalence of selected infectious diseases in cats with uveitis. Journal of the American Veterinary Medicine Association 201 (7) 1005-1009.

7. Davidson MG, Nasisse MP, English RV, Wilcock BP, Jamieson VE (1991) Feline anterior uveitis: a study of 53 cases. Journal of the American Animal Hospital Association 21, 77-83.