27 Proliferative (eosinophilic) keratoconjunctivitis
Typically a young to middle-aged (4–9 years old) domestic short haired cat will be presented due to a change in appearance of one eye. The owners report a pink ‘film’ growing over the eye. Normally the cat is not uncomfortable, or shows only mild blepharospasm. The lesion has often been present for a few weeks but appears to be getting larger. A pale coloured ocular discharge might be reported.
There is normally no history of a predisposing factor. However, it is not uncommon in cats which go out, and owners might think that the cat has possibly been involved in a fight and thus assume that a traumatic incident triggered the development of ocular signs. This is actually rarely the case. The cat might have had a history of previous cat ‘flu but again this is not necessary for the condition to develop. Usually the lesion has been gradually worsening for a few weeks before the cat is brought to the surgery and it is the change in appearance of the eye which alerts the owner to a problem. The lack of apparent pain will frequently explain why there is a delay between the owner noticing the abnormality and presenting the cat. Sometimes a scant, pale, mucoid-type discharge is present, of which the owners have been aware. In some patients both eyes can be affected, although not normally in a symmetrical manner.
General clinical examination is usually normal. On ophthalmic examination menace responses are unaffected and pupillary light reflexes normal. Schirmer tear test readings can be normal, elevated or slightly reduced. Abnormalities are confined to the cornea and conjunctiva with intraocular contents being normal.
A pale pink mass, similar to granulation tissue, is seen extending across the cornea from the limbus. This is usually either at the temporolateral or ventronasal quadrant (Figure 27.1). The conjunctiva adjacent to the lesion is hyperaemic but no chemosis is usually present. A collection of white coloured tissue – almost globules or blobs – can be present on the surface of the pink mass, or adjacent to it. Some whitish discharge can accompany the signs. This looks similar to cottage cheese in consistency. There is normally corneal vascularization. Sometimes the nictitans membrane can be affected – particularly the bulbar side – so this should be examined. Ulceration is not usually a feature of the condition but care must be taken in interpreting fluorescein tests – the excess dye must be thoroughly flushed with sterile saline solution. Uptake of the green dye is quite possible on the pink fleshy tissue itself, often in tiny pinpoint patches, but not actually on the cornea – the epithelium usually remains intact.
Figure 27.1 Proliferative keratoconjunctivitis in the left eye of a 6-year-old domestic short haired cat. Note the pink fleshy matter growing across from the ventromedial canthus and corneal vascularization. A white mucoid discharge is present but no increased lacrimation and minimal ocular discomfort is present.
If the condition is quite advanced, the pink tissue can extend all the way across the cornea and in these cases vision will be affected. The palpebral surface of the eyelids can be involved. Although normally initially unilateral, both eyes can be affected (especially in advanced or untreated cases) but usually to different degrees – the owner might have only been aware of one eye being abnormal but on careful ophthalmic examination it is discovered that the other eye has more subtle lesions (Figure 27.2).
Figure 27.2 Bilateral proliferative keratoconjunctivitis in a domestic short haired cat. The cat’s brother was also affected but only in one eye. No studies have considered inherited tendencies to this condition.
A full ophthalmic examination is obviously required to rule out other causes for the corneal infiltration – an infected ulcer or corneal foreign body for example. The white ‘cottage cheese’ discharge adherent to the granulation-type lesion is often considered pathognomonic but nonetheless further diagnostic tests are recommended to reach a definitive diagnosis. Cytology is the most appropriate test.
Under topical anaesthesia samples are collected from the lesion. This can be done either using a Kimura spatula (or more commonly the blunt end of a scalpel blade) or with a cytobrush. The collected material is gently pressed or rolled onto a microscope slide and allowed to air dry. Staining with Diff-Quik will allow rapid in-house examination of the sample although professional interpretation should also be considered. It is usual to see a collection of epithelial cells, mast cells, neutrophils, lymphocytes and, of course, eosinophils. However, the last are not necessarily abundant, and for this reason the condition can be called proliferative keratoconjunctivitis instead of eosinophilic! If eosinophils are present, it is usual to also find eosinophilic granules within the debris of the cytology samples as well as disrupted cells. Bacterial components are not normally a feature. However, if they are noted, a swab for bacterial culture and sensitivity should be taken.
Swabs can also be submitted for feline herpes virus (FHV-1) polymerase chain reaction (PCR). This is particularly important in cases where a history of upper respiratory infection or previous corneal disease (including ulceration) is present. Since the treatment of eosinophilic keratoconjunctivitis usually requires topical steroids, which can allow FHV-1 recrudescence, identification of this pathogen is particularly important.
Nursing patients with eosinophilic keratoconjunctivitis is minimal and entails topical, and occasionally systemic, medication. Thus owners should be instructed how to apply the medication and with what frequency.