36 Feline eosinophilic plaque
Eosinophilic granuloma complex includes three different entities – eosinophilic granuloma, indolent ulcer and eosinophilic plaque – which, although they have distinct clinical appearances, may have common aetiologies. It is not unusual to see more than one syndrome on the same animal, either at the same time or sequentially. In a small number of cases, cytological examination and a good response to antibacterial therapy confirms bacterial involvement.
Given that eosinophilic granuloma complex is a reaction pattern rather than a diagnosis, a detailed history is invaluable in helping to determine the underlying cause. It is important, therefore, to take a full history, which includes the signalment, age of onset, management and any previous treatments.
In cats with eosinophilic plaque, the lesions are usually located on the ventral abdomen and medial aspects of the thighs. They appear as circular raised, eroded or ulcerated plaques, ranging from 1 to 2 cm in diameter, but they may coalesce into a large lesion several centimetres in length. Uncommonly, lesions may appear on the feet, which usually present with crusting, exudation, erythema and swelling of the plantar or the interdigital skin (Fig. 36.1).
Other variants of the eosinophilic granuloma complex may be found on the same individual, e.g. ‘linear granuloma’, which is seen as a raised chord-like linear plaque, with a yellowish surface, on the caudal aspect of the thighs (Fig. 36.2). Indolent (rodent) ulcer may also be seen as an area of ulceration on the upper lip. Some individuals may also have lesions on the hard or soft palates.
It cannot be stressed enough that eosinophilic granuloma is not a diagnosis but a reaction pattern, and therefore the aim, particularly in cases such as this where the disease was recurrent, is to identify and correct the underlying cause. Amongst other tests, this usually involves therapeutic and diet trials to rule out the involvement of ectoparasitic and microbial diseases, and adverse food reactions. However, the clinician should be aware when undertaking such trials that despite correcting the underlying cause (e.g. avoidance of food allergens in a food allergic cat), the eosinophilic lesions may still not resolve. This is because the lesion is a source of cytokines and other factors (see ‘Aetiopathogenesis’) that not only cause tissue damage, but continue to stimulate eosinophil production in the bone marrow, recruit inflammatory cells to the damaged tissue, increase eosinophil survival time and perpetuate the lesion. Thus, it may be necessary to achieve resolution by therapeutic intervention in addition to investigation of the underlying cause. As might be expected, this complicates assessment of the response to therapeutic and diet trials. These are complex cases and it is important to warn the client at the outset of the time and commitment involved in making a definitive diagnosis.