A 10-year-old West Highland White Terrier is presented for a chronic, non-productive cough.
Thoracic radiographs reveal prominent, thickened bronchial walls, which appear as 'doughnuts' on end-on views and 'tramlines' when viewed longitudinally.
The lung fields appear mildly hyperinflated, but there is no evidence of an alveolar pattern or cardiomegaly.
Which of the following is the most likely diagnosis?
