Successful immunosuppressive treatment of hypersensitivity pneumonitis secondary to lycoperdonosis in a dog.

A 7-year-old neutered male Cocker Spaniel with unrestricted access to rural land presented for progressive lethargy, tachypnea, and cough. Thoracic radiographs showed an unstructured interstitial pattern. Fine-needle aspirate (FNA) lung cytology identified pyogranulomatous inflammation with intralesional mushroom spores. Acute hypersensitivity pneumonitis (HP) was suspected, and treatment was initiated with oxygen supplementation and an immunosuppressive dosage of corticosteroid. Thoracic computed tomography (CT) and bronchoalveolar lavage (BAL) were performed on day 6, month 2, and year 1 to track therapeutic response and assess architectural changes. Clinical signs guided prednisone tapering and discontinuation. One year later, thoracic CT and BAL confirmed re-exposure to mushroom spores with mild persistent inflammation and CT changes suggestive of mixed parenchymal and small airway disease despite absent clinical signs. This case report emphasizes the importance of rapid identification of pulmonary mushroom spores for prompt immunosuppressive treatment. Unlike prior reports of lycoperdonosis with acute, fulminating, and generally fatal outcomes, this dog developed chronic HP.