Thymoma in 11 cats.

Eleven thymomas, 10 benign and 1 malignant, were diagnosed in cats at the Angell Memorial Animal Hospital. Six cats were dyspneic, owing either to the pressure of the tumor or the associated effusion. The effusion in 1 instance contained chyle, and in another, malignant epithelial cells associated with satellite lesions. Three cats had polymyositis, as evidenced clinically by muscle weakness and confirmed by microscopic examination. Two of these also had myocarditis and difficulty in swallowing. In 1 cat, the primary disorder was an atypical, progressive, moist dermatitis that was unresponsive to treatment and that became so severely generalized that the cat had to be destroyed. The thymoma was discovered only at necropsy.U