Pyothorax in Cats

By Malcolm Weir, DVM, MSc, MPH; Krista Williams, BSc, DVM; Ernest Ward, DVM

What is pyothorax?

Pyothorax is the presence of inflammatory fluid or pus within the chest cavity, which is the area between the lungs and the inner walls of the ribs.

What causes pyothorax?

Pyothorax is usually caused by a bacterial infection in the chest cavity. In most cases, pus is present in both sides of the chest, although occasionally, only one side will be affected.

The source of the infection is rarely found, with only 35-67% of cases being identified. Possible causes include:

  • Penetrating wounds to the chest wall, such as a bite wound (the most common cause of pyothorax in cats)
  • Wounds to internal structures, such as the esophagus or trachea (windpipe), especially following ingestion or inhalation of a foreign object
  • a migrating foreign body, such as a grass seed that entered the body elsewhere
  • Spread of an infection from the lungs
  • Spread of infection through the bloodstream
  • Secondary to cancer

What are the clinical signs of pyothorax?

Rapid, shallow, open-mouthed breathing that may be painful, depression, lethargy, decreased appetite, and other signs of general illness are seen in most cats with pyothorax. Affected cats usually have a high temperature contributing to some clinical signs. Rapid, open-mouthed breathing or breathlessness is caused by fluid in the chest preventing the lungs from expanding normally. The severity of these signs is highly variable, and cats may suddenly die without any previous signs of illness.

How is pyothorax diagnosed?

Clinical examination by a veterinarian, particularly listening to the chest with a stethoscope, may indicate fluid in the chest. In mildly affected cases, chest radiographs (X-rays) will be performed to determine the presence and location of fluid in the chest. An ultrasound of the chest cavity may also be recommended. Additional supporting diagnostics may include a complete blood count (CBC), a biochemical panel, and a urinalysis.

In severe cases, it may be necessary to drain the fluid out of the chest immediately (a procedure called a thoracocentesis or chest tap) before taking radiographs. The patient may need to be sedated for this procedure. In many cases, the pus from both sides of the chest can be drained from one side, although it may be necessary to drain both sides in some cats. Sometimes, the fluid is in pockets, and multiple drainage procedures must be performed. Your veterinarian will send the fluid samples to a laboratory for evaluation and bacterial culture and sensitivity testing so that the correct antibiotic can be administered.

In cases of pyothorax with no apparent cause, the cat should be tested for feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV).

How is pyothorax treated?

Draining the infected fluid plays an essential part in treating this condition. Drainage may be needed on multiple occasions during the initial treatment period. In most cases, a flexible catheter will be inserted into the chest to remove the fluid. The tube may also flush the chest cavity with fluids (lavage).

In some cases, a chest drain may be inserted surgically, allowing drainage of the chest and administration of antibiotics into the chest cavity. The drain may be left in place for several days to allow these procedures to be repeated. Surgery may also be required to identify and remove necrotic (dead) tissue and foreign material from the chest cavity.

"Drainage may be needed on multiple occasions during the initial treatment period."

Treatment with oral antibiotics is essential and may be prescribed for several weeks. In very sick cats, supportive treatment with intravenous (IV) fluids may also be needed in the initial stages.

What is the long-term outlook for a cat with pyothorax?

This depends on the cause of the disease. In cases where no underlying disease is found, the outlook is good if the cat survives the critical initial stages. Unfortunately, some cats will die in the early stages of their disease, although an overall survival rate of 62% has been reported.


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