Limbal melanoma

56 Limbal melanoma




INITIAL PRESENTATION


Abnormal appearance – swollen/colour change



PRESENTING SIGNS


The condition can be seen in dogs (particularly German shepherd dogs and Labrador retrievers) and less commonly in cats, and owners present the patient because they have noticed a change in appearance to the eye. Normally only one eye is affected. They have noticed a dark lesion at the junction between the white and clear parts of the eye which is slightly raised and enlarging. Most commonly the lesion is at 12 o’clock but it can be anywhere around the circumference of the cornea. The lesion has usually been noted a few days or even weeks prior to presentation but since the pet shows no signs of discomfort or visual impairment the owners do not tend to present them immediately on noticing the lesion. Indeed, sometimes they will have been aware of it for many months and only point it out to the clinician when the pet is presented for another reason such as vaccination.



CASE HISTORY


The patient is normally clinically well with no relevant current or previous systemic or ocular problems. No treatment has usually been given for the ocular lesion and the owner has been aware of it slowly enlarging.



CLINICAL EXAMINATION


General clinical examination is normal. On ophthalmic examination the patient has normal menace responses and vision is unaffected. Mild localized conjunctival hyperaemia can be present but the eye is certainly not red or inflamed in appearance. No significant ocular discharge is present. A smooth, shiny, raised pigmented mass is present at the limbus. Occasionally it is only poorly or non-pigmented but most are very dark in colour. The lesion covers the limbus and extends into the cornea, with some localized corneal oedema around it. Sometimes an arc of corneal lipid is also present distal to the lesion (lipid keratopathy). It is usually 3–5 mm in diameter on presentation. It is most frequent between the 12 and 3 o’clock position but can be situated anywhere around the limbus – ventral and ventromedial lesions are often much larger before being presented simply because they are more difficult to see. Pupillary light reflexes are normal and no dyscoria is present. The iris is unaffected – it is of normal colour and shape. Viewing the patient from the side with a pen torch will reveal that the lesion is outside the globe and does not include the iris. No uveitis or other intraocular changes are present. Intraocular pressure is normal.




DIFFERENTIAL DIAGNOSES



• Uveal melanoma (see Figure 37.2)

• Extension of ciliary body melanoma (see Figure 37.6)

• Corneal/scleral laceration with iris prolapse (see Figure 24.1)

• Nodular episcleritis

• Pigmentary keratitis

• Foreign body

• Feline sequestrum (see Figure 30.1)


CASE WORK-UP


The main differential for limbal melanoma is extension from a uveal (i.e. iris or ciliary body) neoplasm. This can be achieved by ultrasonography. A limbal melanoma will be seen as a raised mass on the outside of the globe – a stand-off is necessary to allow visualization of such superficial lesions (a surgical glove filled with water or ultrasound gel works very well). A uveal melanoma will show thickening, and usually a discrete mass, within the iris/ciliary body, which then extends outwards towards or even through the sclera. In addition, other ocular signs are more commonly present with uveal tumours (see Table 56.1).


Table 56.1 Differentiation between uveal and limbal melanoma

































Uveal melanoma Limbal melanoma
Dyscoria can be present Pupil normal
Darkening of iris Iris normal colour
Mass visible within iris Mass on surface of globe
Uveal inflammation common No uveitis
Intraocular pressure can be low Intraocular pressure normal
Drainage angle can be affected Drainage angle normal
Difficult to biopsy Relatively easy to biopsy
Relatively common Uncommon
Low risk of metastasis in dogs (4%), higher in cats (60%) Metastasis not reported

Gonioscopy is also recommended and referral for this should be considered. With a limbal melanoma there will be no involvement of the drainage angle, while uveal melanomas normally result in pigment deposition and closing of the iridocorneal angle in the affected sector.


Biopsy might be necessary if there is any doubt over the pathology involved, especially if the lesion is poorly or non-pigmented, and thus similar in appearance to nodular episcleritis. Although this can be done with sedation and topical anaesthesia, it is frequently more sensible to anaesthetize the patient.




NURSING ASPECTS


Patients with limbal melanoma are normally surgical candidates and require topical medication postoperatively. Nurses should ensure that owners are capable of applying this but no other specific care is required.

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  4. Chronic superficial keratitis

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Sep 10, 2016 | Posted by in SMALL ANIMAL | Comments Off on Limbal melanoma

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