11 Jul 2016

Lower airway diseases in felines

Sally Birch discusses the case of Arthur, an 11-year-old male neutered Siamese cat that presents with a chronic history of coughing and wheezing.

Sally Birch

Figure 1. The lateral thoracic radiograph.

Your first out-of-hours case at the weekend is Arthur, an 11-year-old male neutered Siamese cat.

Arthur has a chronic history of coughing and wheezing, and has presented to you severely dyspnoeic. You are able to carefully acquire conscious dorsoventral and lateral radiographs of the thorax. The lateral radiograph is presented in Figure 1.

Question

How would you interpret this radiograph?

Answer

Arthur is in poor body condition. There is moderate hyperinflation of the lung fields and caudal displacement and flattening of the diaphragm. Throughout the lungs there are multiple subtle soft tissue rings and tramlines representing thickened bronchial walls (Figure 2; yellow arrows).

The aorta is prominent and mildly undulating, consistent with redundancy – a common incidental finding in older cats. On examination of the skeleton, multiple rib fractures of different ages at varying stages of healing are present (Figure 2; white arrows).

The colon and stomach are moderately dilated, with gas most likely due to aerophagia. A cluster of small, rounded mineral opacities are present in the cranioventral abdomen. On close inspection, these are surrounded by a soft tissue wall and represent choleliths in the gall bladder. In this instance, they are an incidental finding unrelated to the presentation.

Figure 2. The radiograph in Figure 1 showing thickened bronchial walls in the lungs (yellow arrows) and rib fractures at varying stages of healing (white arrows). — **Figure 2**. The radiograph in **Figure 1** showing thickened bronchial walls in the lungs (yellow arrows) and rib fractures at varying stages of healing (white arrows).

In summary, Arthur’s radiograph reveals evidence of a bronchial pattern and lung hyperinflation consistent with feline chronic lower airway disease, also known as feline asthma. The condition is thought to result from a type I hypersensitivity reaction to inhaled allergens. Siamese cats appear particularly predisposed to airway disease, although any breed may be affected.

Hyperinflation of the lungs occurs due to temporary bronchial constriction and air trapping. Rib fractures are commonly seen in cats with respiratory disease as a result of severe coughing and/or dyspnoea. While rib fractures can occur anywhere, they preferentially affect the dorsal aspect of the caudal ribs, since this represents the point of insertion of the serratus dorsalis caudalis muscle.

Figure 3 is a lateral radiograph of another cat with findings typical of severe feline lower airway disease.

This cat has a severe bronchial lung pattern and several thickened bronchial walls are visible (yellow arrows). Another common finding is the presence of one or more small mineralised foci in the lungs (white arrow). These represent bronchial microlithiasis (mineralised plugs of mucus in the bronchial lumen) or mineralisation of peribronchial mucous glands.

Figure 3. Lateral radiograph of the thorax of a cat with severe lower airway disease, showing bronchial walls (yellow arrows) and small mineralised foci in the lungs (white arrow). — **Figure 3**. Lateral radiograph of the thorax of a cat with severe lower airway disease, showing bronchial walls (yellow arrows) and small mineralised foci in the lungs (white arrow).

The two conditions cannot be differentiated radiographically and usually considered to be incidental findings. Occasionally, soft tissue nodules are seen in the lungs of asthmatic cats due to the presence of eosinophilic granulomas or accumulation mucus in bronchi seen end-on. Right middle lung lobe collapse is another common finding in these cats and thought to be due to mucus plugging the bronchus supplying the lobe, leading to resorption atelectasis.

Great care should be taken when attempting to radiograph a dyspnoeic cat. Some cats will not tolerate the procedure and it may need to be delayed until the cat is more stable. One option is to radiograph the cat while it is stood on a radiographic cassette placed in the bottom of a wire basket. It is important to remember to open the lid, otherwise a metal grid will appear on the film.

A towel placed over the top of the basket acts as a temporary lid. While radiographs obtained this way are not of the best quality with regards to positioning, they may be sufficient for a diagnosis, require minimal handling and minimise stress to the cat.