14 Exfoliative dermatitis with thymoma
Exfoliative dermatitis has been described in association with thymoma, both in people and in cats. A number of well-recognized paraneoplastic syndromes, such as cachexia, leucocytosis, hypercalcaemia and hyperglycaemia, are due to the systemic effects of hormones and/or other factors produced by the tumour, or its metastases, rather than the direct effect of the neoplastic invasion itself. In rare cases paraneoplastic signs such as exfoliative dermatitis, erythema multiforme, myasthenia gravis, myositis and myocarditis have been associated with thymoma.
In some of these cases, the paraneoplastic syndrome can be more life threatening than the tumour. Early recognition of such syndromes and appropriate treatment can lead to resolution of the clinical signs, and improve the quality of life and the survival time of the patient. This chapter describes the cutaneous clinical presentation in a cat with a thymoma.
Most cats with thymoma present with a history of dyspnoea, coughing, lethargy and anorexia, which are often associated with the presence of a large space-occupying mass in the cranial mediastinum. The onset of cutaneous signs is usually sudden, with no previous history of dermatological disease. As most affected cats are old, owners often relate some of the signs, such as lethargy or changed demeanour, to age. The appetite in most cases is unaffected.
This condition is characterized by moderate to severe exfoliation, erythema and alopecia, affecting mainly the face and the pinnae. The lesions may progress to the dorsum and the legs, and may eventually involve the whole body. Secondary bacterial and Malassezia infections can further complicate the disease.