Microlithiasis associated with chronic bronchopneumonia in a cat

Chronic bronchopneumonia associated with microlithiasis was diagnosed in a 9-year-old domestic shorthair cat with a 3-month history of coughing and dyspnea. Thoracic radiography revealed multifocal patchy alveolar infiltrates in all lung fields. Numerous acellular, concentrically laminated, periodic acid-Schiff-positive microliths were seen in mucus from tracheal washing. Microliths were composed primarily of calcium carbonate. A definite cause could not be identified. There was no response to treatment and the cat was euthanatized. Marked type-II alveolar cell proliferation, peribronchiolar smooth muscle proliferation, and alveolar microlithiasis were seen histologically. Microliths are rarely encountered in tracheal washings from companion animals. Their pathophysiologic properties and meaning remain to be established.