Also known as pleural empyema, pyothorax is the presence of pus in the pleural space in the chest cavity, the thin, fluid-filled space that lies between the lungs and the chest wall.
Normally a small amount of fluid is located in this space (5 ml or less), which allows for the smooth movement of the structures in the thorax during respiration. Small blood vessels in the pleural lining produce this fluid, blood and lymph nodes take away any excess to keep it in balance. Pyothorax is a septic form of pleural effusion, which is covered here.
Any pathogenic organism can potentially cause pyothorax including fungal, viral, bacterial or protozoal, however, is almost always caused by a bacterial infection. The collection of pus is due to dead white blood cells and dead bacteria. Common bacteria involved in pyothorax include Pasteurella spp (the most common), Nocardia spp, Streptococcus spp, Clostridium spp, Proteus spp, Bacteroides spp and Mycoplasma spp. Less common causes include toxoplasma (protozoa), cryptococcosis and Blastomyces (fungal infections). Most cases of pyothorax are polymicrobial, meaning more than one type of organism is involved.
There are no breed predispositions. The average age of cats who develop pyothorax is 4-6 years, however, cats of any age can be affected. Multiple cat households have a greater incidence as well as entire male cats who are allowed to roam outside, presumably because of the increased risk of bite wounds.
How do cats develop pyothorax?
There are several possible ways cats can develop pyothorax. In many cases, the initial cause may remain undetermined.
- Penetrating bite wounds to the thorax
- Penetrating trauma to the thorax
- Inhalation of foreign object such as a grass awn
- Bacteria ascending from the mouth into the pleural space
- Extension from other sites such as lungs (pneumonia) or bronchi
- Diffusion of bacterial infection via the blood from distant source
- Parasitic migration
- Perioperative aspiration (aspiration of gastric contents during anesthesia)
- Oropharyngeal aspiration from upper respiratory infection
- Ruptured abscess
- Lung lobe torsion
What are the symptoms of pyothorax in cats?
As fluid builds up in the pleural cavity, the lungs become compressed, making it harder for your cat to breathe. Symptoms may progress slowly, over a period of time and can include:
- Dyspnea (difficulty breathing)
- Tachypnea (rapid breathing)
- Exercise intolerance
- Anorexia (loss of appetite)
- Weight loss
- Dull hair coat
- Blue-tinged gums and tongue due to cyanosis
How is pyothorax diagnosed?
Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you. During the examination, the veterinarian will listen to your cat's heart and lungs with a stethoscope which may reveal muffled heart and lung sounds.
Before any tests are carried out, your cat will need to be stabilised if they are severely dyspneic.
Diagnostic tests will be necessary, and these may include:
- Biochemical profile, complete blood count, and urinalysis. White blood cell count may be elevated and anemia may be present. Biochemical profile is usually normal, although hypoalbuminemia may occur. Other findings may include protein in the urine, elevated liver enzymes, elevated urea, creatinine, electrolyte imbalances and increased bile acids.
- Radiographs of the chest to look for the presence of unilateral or bilateral pleural effusion, foreign objects or tumours.
- CT scan to look for penetrating injury, foreign object or lung lobe torsion.
- Thoracocentesis (pleural tap) is a procedure in which a needle is inserted into the pleural cavity to remove excess fluid.
- Cytology (microscopic examination of the cells) : Analysis of the thoracic fluid removed from the pleural cavity during thoracocentesis.
- Fluid samples should be submitted for aerobic and anaerobic bacteria culture and sensitivity.
- Abdominal ultrasound to look for other organ involvement, abscess, structural abnormalities or foreign body.
- FIV and FeLV testing may be recommended in cases of pyothorax where an underlying cause can't be determined.
How is pyothorax treated?
Treatment is aimed at relieving symptoms and antibiotics which may be required for up to six weeks. Your cat will need to be hospitalised until the infection can be brought under control. While he is in care the following will be carried out:
- Respiratory support such as oxygen therapy, bronchodilators or nebulisers may be necessary. Cats are often very sick and need to be treated with great care. Your veterinarian may be placed in an oxygen tent to stabilise him.
- Thoracic drainage tubes will be inserted to remove fluids from the pleural cavity. Local anesthesia and IV sedation will be given to keep your cat comfortable during this procedure. Tubes will be flushed several times a day with 0.9% saline or lactated Ringers solution warmed to body temperature to wash the chest cavity (pleural lavage). Tubes will need to remain in place for between 4-6 days. An Elizabethan collar will be required while tubes are in place. Cats will need to be hospitalised while tubes are in place.
- Cytologic examination of the fluids removed should be checked daily to look for signs of resolution.
- Broad-spectrum IV antibiotics will initially be given until cytology results return, and then antibiotic therapy will be tailored to the specific type of bacteria present.
- Pain medication.
- Supportive care including IV fluids to correct dehydration, increase blood volume and electrolyte imbalance.
- Nutritional support if your cat is not eating. A feeding tube may be required.
- Surgery may be necessary to remove foreign objects and masses, treat abscesses or lung lobe torsion and debridement of damaged tissue.
- Exploratory surgery in cases which are unresponsive to antibiotics.
Your cat will be sent home with oral antibiotics, always administer as instructed. Cats will require long-term antibiotic therapy.
Repeat radiographs will be regularly performed, antibiotics will continue for at least a month after the infection has cleared and radiographs show all evidence of fluid/pus build up has resolved.
He will need to be on cage rest or confined to a small, quiet room while he recuperates.
What is the prognosis for pyothorax in cats?
If the owner is willing to follow the veterinarian's instructions the prognosis fair. This includes medicating for several weeks and regular follow-up appointments and chest radiographs.