Computed Tomography-Derived Bronchial Wall Indices in Cats with Clinical and Serological Features Compatible with Heartworm-Associated Respiratory Disease

Abstract

Heartworm-Associated Respiratory Disease (HARD) is an early manifestation of feline dirofilariosis caused by immature Dirofilaria immitis stages reaching the lungs and inducing marked inflammatory airway lesions. This study quantified computed tomography (CT)-derived bronchial wall remodeling in cats with clinical and serological features compatible with HARD using the bronchial wall-to-bronchus (BW/B) and bronchial wall-to-pulmonary artery (BW/A) ratios. Twenty-seven client-owned cats were prospectively included: 19 cats with lower-airway clinical signs and D. immitis antibody seropositivity, considered compatible with HARD, and 8 asymptomatic seronegative cats that underwent CT for non-cardiorespiratory clinical indications. All underwent thoracic CT under a standardized anesthetic protocol. Bronchial lumen diameter, total bronchial diameter, and pulmonary artery diameter were measured in cranial and caudal lung regions, and bronchial wall thickness was calculated to derive BW/B and BW/A. Cats compatible with HARD showed significantly increased bronchial wall thickness and higher BW/B and BW/A ratios across all evaluated lung lobes, supporting diffuse bronchial remodeling. BW/A was the only index showing a significant area-by-group interaction, suggesting a possible regional distribution pattern of bronchial wall remodeling in affected cats. Measurement repeatability and reproducibility were high overall. CT-derived bronchial wall indices, particularly BW/A, may provide an objective complementary tool for characterizing airway involvement in cats with clinical and serological profiles compatible with HARD. Because antibody seropositivity indicates exposure rather than confirmed active infection, and because of the small control group, absence of respiratory disease comparators, and lack of histopathological validation, these findings should be considered preliminary and descriptive.