Focal streptococcal pneumonia associated with a granular cell tumour in a horse

Summary This report describes a chronic focal pulmonary infection with Streptococcus zooepidemicus in an adult horse, secondary to mechanical compression caused by a granular cell tumour. Ante mortem diagnosis was based on clinical history, deep lower airway endoscopy and thoracic ultrasonography. The horse failed to respond to prolonged antimicrobial therapy despite confirmed antimicrobial susceptibility. The diagnosis was confirmed postmortem. To the authors’ knowledge, this is the first report describing the combined use of thoracic ultrasonography and airway endoscopy as diagnostic tools for a pulmonary granular cell tumour in a horse. Pulmonary tumours, particularly granular cell tumours, should be considered a potential underlying cause in horses with persistent bacterial lower airway infections that are unresponsive to appropriate conservative therapy.