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Pyothorax in Dogs

Pyothorax occurs when pus accumulates in the chest (pleural) cavity in response to an infection. Made up of white blood cells (neutrophils) and dead cells, pus is the body's natural immune response to an infection. Eventually, the white blood cells die, leaving the thick whitish-yellow fluid that is characteristic of pus.

Pus that accumulates in the chest cavity, however, differs from an abscess, in that it does not create an enclosed wall of tissue to inhibit the bacteria from spreading. Instead, the pus forms into sacs that line the pleura, eventually scarring the cavity and severely impairing lung function.

A bacterial infection that settles in the chest cavity can enter from the lungs or esophagus. Dogs generally get these types of infections from inhaling foreign objects like grass awns (bristles on the tips of grass), or from chest piercing wounds. Hunting dogs and sporting breeds are most likely to develop such infections.

The condition described in this medical article can affect both dogs and cats. If you would like to learn how pyrothorax affects cats, please visit this page in the PetMD health library.

Symptoms and Types

Some common symptoms associated with pyrothorax include:

• Cough
• Fatigue
• Low-grade fever
• Chest pain or discomfort
• Loss of appetite (anorexia)
• Weight loss (sometimes the only sign)
• Increased, or decreased breathing rate
• Collapse after exercise with slow recovery of energy
• Recent history of fights or puncture wounds

Causes

The most common causes for pyrothorax include infections with the bacteria:

• Bacteroides
• Peptostreptococcus
• Fusobacterium
• Corynebacterium
• Escherichia coli
• Pasteurella
• Streptococcus

Other causes include bacterial and fungal infections, which are usually due to agents found in the soil; e.g., actinomycosis, nocardiosis

Diagnosis

You will need to give a thorough history of your dog's health as well as its symptoms and and possible incidents that might have preceded this condition, such as any fight wounds or chest injuries your pet might have sustained.

Your veterinarian will perform a thorough physical exam, checking your dog’s chest for inflammation of cellular tissue (cellulites) or scarring. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, an electrolyte panel. In addition a  urinalysis sample of fluid from the chest cavity will be sent to the laboratory for cytologic (microscopic) evaluation and gram staining -- a procedure that makes bacteria more visible by causing it to stand out from the other cells.

A sample of the fluid in the pleural cavity will be sent for aerobic and anaerobic bacterial cultures (bacteria that need oxygen, and bacteria that does not, respectively), and for serological testing to detect the presence of a fungal agent. If parasite S. lupi is suspected, an examination of the esophagus (esophagoscopy) can be done.

Your veterinarian can also use X-ray and ultrasound imaging to examine the interior of the dog's chest cavity. These images will show fluid in the chest cavity, possible lung hardening (consolidation), lung collapse, and/or masses.