Transmission or Cause: The cause of this condition is unknown. Precipitating factors include medications, dietary substances, vaccines, and some infections, possibly including feline herpes virus and canine parvovirus. In many cases, the cause is idiopathic.
Affected Animals: An uncommon to rare skin disorder that can affect both dogs and cats.
Clinical Signs: The lesions associated with Erythema Multiforme can be vast and variable, but generally will present acutely and have a symmetrical appearance. In most cases, dogs and cats will have reddened flat or slightly elevated lesions that may or may not be crusted.
Other clinical signs can include vesicles, bullae, ulcers, hives, hair loss and scaling. Lesions are typically found in the inguinal, axillary or head region but may also be found in the oral cavity, on foot pads, ears and mucocutaneous junctions.
Humans with Erythema Multiforme will generally develop a typical target lesion, which is a round, sharply demarcated lesion with a least three different zones of color: a dark red disk is surrounded by concentric rings of edematous tissue and peripherally located reddened tissue. Although animals can develop similar lesions, they rarely develop the human equivalent of the typical target lesion. Some animals will present with systemic signs of illness, including fever, anorexia and depression.
Diagnosis: Diagnosis is made via clinical presentation in conjunction with biopsy.
Treatment: Many cases of Erythema Multiforme are mild and may be self-limiting. In any case, attempts to identify and correct underlying causes should be made. In cases of persistent disease, then immunosuppressive medications, such as prednisone, cyclosporine and azathioprine may be beneficial. However, when medications are tapered, recurrences can occur especially in idiopathic cases.
Prognosis: Prognosis is guarded to fair depending on the severity of the skin lesions, whether an underlying cause can be identified and treated, and overall response to treatment.