Ulcerations and Erosions
Definition
An ulcer is a cutaneous defect that results from a complete loss of the epidermis and usually part of the underlying dermis.7 Ulcers often heal with scarring that is caused by destruction of dermal collagen.
An erosion is a cutaneous defect that results from a partial loss of the epidermis that does not penetrate beneath the basal laminar zone. Because an erosion does not involve the dermis, it heals without leaving a scar. Because the epidermis is a cutaneous barrier to invading microorganisms, ulcers and erosions are often secondarily infected.Mechanisms of Ulcer and Erosion Formation
Ulcers and erosions are secondary lesions. Primary lesions develop spontaneously and are a direct reflection of underlying disease. Secondary lesions evolve from primary lesions or are artifacts induced by excoriation or external trauma. Primary lesions that may lead to the formation of ulcers and erosions include fluid-filled lesions such as pustules and vesicles. Rupture of these fragile lesions results in epidermal destruction and erosion or ulcer formation. Swellings such as abscesses and cysts may also rupture, resulting in ulceration, but these primary lesions are more stable and often remain intact. Nodules and tumors may become secondarily eroded or ulcerated. As the nodule or tumor enlarges, the mass exerts pressure on the overlying epidermis, leading to epidermal atrophy and ultimately a break in epidermal confluence, resulting in ulceration and erosion. The most common cause of ulceration and erosion is pruritus, which induces excoriation and hence epidermal destruction. Ulcers and erosions may also result from external trauma such as epidermal destruction arising from mechanical, thermal, or chemical causes (Box 11.3).
Approach to the Diagnosis of Ulcerations and Erosions
To diagnose the cause of an ulcer or erosion, the clinician must first determine the primary lesion that resulted in ulceration and erosion.
Ulcers and erosions occurring secondary to pustules and vesicles, to swellings such as abscesses and cysts, to nodules and tumors, to pruritus, and to external trauma must be differentiated. The list of differential diagnoses relevant to each of these groups of primary lesions is then considered.■ BOX 11.3
Most Common Causes of Ulcerations and Erosions in Horses and Ruminants
Immune-Mediated
Adverse drug reaction
Contact irritant or hypersensitivity
Photosensitivity
Purpura hemorrhagica (horses)
Vasculitis
Infectious
Dermatophilus congolensis
Habronema species (horses)
Viral diseases (in ruminants; e.g., infectious bovine rhinotracheitis, vesicular stomatitis, bovine herpes mammillitis)
Neoplasia
Squamous cell carcinoma
The following steps are a guide to the diagnosis of ulcerations and erosions in horses and ruminants:
1. History (see Fig. 11.2)
a. Determine if the animal is pruritic.
b. Determine if the animal has been subjected to external trauma (mechanical, thermal, or chemical).
c. Determine what topical and systemic medications were given to or used on the patient before the onset of the problem. Use of certain topical agents may suggest a diagnosis of contact dermatitis, whereas administration of systemic medications may suggest a drug hypersensitivity.
2. Physical examination (see Fig. 11.2)
a. Examine the oral cavity and mucocutaneous junctions for lesions. Oral or mucocutaneous lesions (or both) in the horse might suggest accidental ingestion of a vesicant or the rare diagnosis of bullous pemphigoid or pemphigus vulgaris. In a ruminant these lesions are often seen with viral infections.
b. Look for evidence of excoriation, suggesting that the ulcerations and erosions have occurred secondary to pruritus.
c. Look for evidence of primary lesions such as pustules, vesicles, nodules, tumors, or swellings, which may have preceded the ulcerations and erosions.
3. Biopsy for routine histopathologic examination
4. Biopsy for direct immunofluorescence testing