Max’s clinical signs (tachypnea, increased expiratory effort) and auscultation findings support lower airway disease, so you recommend a thoracic radiographic examination as your first diagnostic step. The owners agree, and these are the findings:
Diffuse miliary, nodular, interstitial disease is present with a bronchial component. There is patchy coalescence of the pathology in areas, particularly the left caudal lobe. The cardiac silhouette appears normal in size and shape. No evidence of pleural fluid is seen. The rest of thoracic cavity appears normal.
Based on these radiographic findings, which of the following is the least likely to be a differential diagnosis for this case?