Pneumothorax secondary to Dirofilaria immitis infection in two cats.

Dirofilariasis was diagnosed in 2 cats with spontaneous pneumothorax. One cat had a 3-week history of a cough, and the other had an 11-month history of vomiting and tachypnea. Pneumothorax was managed in cats by thoracocentesis and supportive care. Diagnosis of dirofilariasis was made on the basis of heartworm antigen and antibody test results and radiographic findings. Clinical signs of heartworm infection improved after treatment with corticosteroids. Cats had good extended outcomes. Heartworm disease should be one of the differential diagnoses considered in cats with spontaneous pneumothorax.