[Pathomorphology of chronic obstructive lung disease in the horse]

The chronic obstructive pulmonary disease (COPD) in horses is primarily based on a chronic bronchitis/bronchiolitis with constriction of the tubes in the lower respiratory tract. The outward appearance of the lung is characterized by a diffuse or marginal alveolar emphysema. The big bronchial tubes are usually not altered. Small bronchi and bronchioli can often be seen through the pulmonal pleura. On the sectional area they are visible as opaque grey-red nodules with a central lumen detectable under a magnifying glass. The histopathological picture of alterations in the bronchial tree can vary from case to case. In the smaller bronchi and bronchioli, three basic types of inflammatory and obstructive processes can be distinguished: Type 1: accumulation of mucous exudate in the bronchial tubes and bronchioli, in some cases also in the alveoles; Type 2: desquamative purulent bronchitis/bronchiolitis; Type 3: non-purulent peribronchitis/peribronchiolitis. Indications of a chronic process cannot always be demonstrated. Interstitial lymphocytic infiltrations can be regarded as a manifestation of the chronic course. Hypertrophy of the muscles of the bronchi, metaplasia of the epithelium, fibrosis of the bronchial walls and the neighboring alveoles with hyperplasia of the epithelium are rarely found. The histopathological picture is representative for the final stage of pulmonary diseases without any hint as to the etiology. However, if eosinophilic granulocytes are detected in the peribronchial tissue, an allergic origin is most likely.