When an ulcer hasn’t healed at the first recheck, there is a tendency to throw up our arms and become frustrated. However, ulcers within this group have actually helped us by identifying themselves as “complicated ulcers” with one of only 3 causes possible in dogs and one of only 2 causes possible in cats.
Reasons Feline and Canine Ulcers Do Not Heal
Based upon their clinical appearance including their fluorescein staining pattern, nonhealing ulcers can be defined as likely due to one of three causes in dogs:
- The primary cause is still present
- It is an indolent ulcer (also known as Boxer ulcers or superficial chronic cornea epithelial defects - SCCEDs)
- It has become bacterially infected
The thought process is even simpler for cats. Because cats do not get SCCEDs, there are only 2 reasons an ulcer has not healed in cats - the primary cause is still present (and feline corneal ulcers are considered to be due to feline herpesvirus (FHV-1) until proven otherwise), or the ulcer has become bacterially infected.
Fortunately, each of the ulcer complications has a characteristic appearance:
- Ulcers in which the primary cause is still present typically appear like simple ulcers but remain chronic. That is, they don’t necessarily worsen; they just don’t heal. This should stimulate a detailed search for all of the known causes of ulcers (figure 1).
- Indolent ulcers as defined by the failure of epithelium to adhere to stroma due to a primary adhesion defect are seen in dogs only, typically boxer dogs or corgis of any age or older dogs of any breed. By definition, they are superficial, uninfected, chronic (or will become chronic), and have a lip of redundant non-healing corneal epithelium that is easily debrided with a cotton-tipped applicator (CTA). This lip often produces a characteristic “halo” fluorescein staining-pattern due to leakage of stain under the non-adherent lip. They arise from a failure of replicating and migrating epithelium to complete the final step in healing - to adhere to the underlying stroma via the epithelial basement membrane. Diagnosis is reliant on characteristic signalment, chronicity, appearance and staining-pattern of the ulcer, as well as the ease with which the epithelium is manually debrided with a CTA.
- Bacterially infected ulcers have one or more of 3 features in any combination - stromal loss (i.e., the ulcer is deep), corneal malacia (or “melting”), and/or infiltration of the stroma with white blood cells (which turns the stroma yellow-green).
Using these guidelines, figure 2 outlines an algorithmic approach to nonhealing ulcers in dogs and cats.